l a w o f f i c e s o f treet uite … · the technical memorandum being submitted in this filing...

L A W O F F I C E S O F 1 5 0 0 K S T R E E T , N W ♦ S U I T E 3 3 0 ♦ W A S H I N G T O N , D C 2 0 0 0 5

GGG KKK RRR SSS EEE 202.408.5400 ♦ FAX: 202.408.5406 ♦ WEBSITE: www.gkrse-law.com

November 10, 2010 Ms. Kimberly Bose Secretary Federal Energy Regulatory Commission 888 First Street, NE Washington, DC 20426 RE: Public Utility District No. 1 of Okanogan County, Enloe Hydroelectric Project, FERC Project No. 12569; Analysis of Proposed Bypass Reach Minimum Instream Flow Requirements

This letter provides supplemental information to the Federal Energy Regulatory Commission (“FERC” or “Commission”) regarding ongoing consultation by the Public Utility District No. 1 of Okanogan County (“District”) with the Washington Department of Ecology and Washington Department of Fish and Wildlife, as part of the 401 Water Quality Certification process for the proposed Enloe Hydroelectric Project, FERC Project No. 12569 (“Project”).

On October 28, 2010, the District provided supplemental information to the Commission, reporting on a consensus regarding bypass reach minimum instream flows associated with the Project. The technical memorandum being submitted in this filing includes the evidence and background information currently known by the District in connection with this matter. The District has consulted with the Washington Department of Ecology and the Washington Department of Fish and Wildlife on this information. The technical memorandum includes information included in a May 2010 paper entitled “Draft Analysis of Proposed Bypass Reach Instream Minimum Flow Requirement,” as well as additional information regarding: (1) a more detailed analysis to address the remaining questions about the potential for warming within the bypass reach at the proposed instream minimum flows; as well as (2) a description of design concepts proposed in conjunction with the 10 cfs and 30 cfs minimum instream flows; and (3) a description of fish surveys completed in the bypass reach in September 2010.

Also included in this filing is a letter prepared by Washington Department of Fish and

Wildlife fish biologist Hal Beecher reporting results of a snorkel survey of the bypass reach conducted on September 15, 2010 to supplement the Commission’s record.

L A W O F F I C E S O F

GGG KKK RRR SSS EEE

Should you have any questions or comments, please contact the undersigned or the District’s Enloe Project Manager, Dan Boettger at (509) 422-8425.

Respectfully Submitted,

Donald H. Clarke Counsel to Public Utility District No. 1 of Okanogan County

Attachments: Enloe Bypass Flows Technical Memorandum;

Washington Department of Fish and Wildlife report on September 15, 2010 snorkel survey.

CERTIFICATE OF SERVICE

I hereby certify that I have on this day served the foregoing document

by email or first class mail postage prepaid upon each person designated on the

official service list compiled by the Secretary of the Commission in this

proceeding.

Dated at Washington, DC this 10th day of November 2010.

Manuel Sandoval Legal Assistant Law Offices of GKRSE

1500 K Street, NW, Suite 330 Washington, DC 20005

Enloe Bypass Flows Technical Memorandum

Prepared for Public Utility District No. 1 of Okanogan County November 2010 Page 1

Cardno ENTRIX 200 First Avenue West, Suite 500

Seattle, WA 98119 (206) 269-0104 | Fax (206) 269-0098

www.cardnoentrix.com

Technical Memorandum

Date: November 10, 2010

To: Public Utility District No. 1 of Okanogan County

Washington Department of Ecology

From: Jeremy Pratt - Cardno ENTRIX

RE: Analysis of Proposed Bypass Reach Minimum Instream Flow Requirements for Enloe Hydroelectric Project

1.0 BACKGROUND In the previous licensing proceeding for the existing Enloe Hydroelectric Project (Project), FERC issued a license in 1996 (subsequently rescinded) that provided for instream flow releases through a bypass reach from the dam to the old powerhouse facility that was considerably longer than is currently proposed. The purpose was to protect anadromous fish habitat in the Similkameen River below Similkameen Falls (Falls).

As a result of early consultation in the current license proceeding, the District proposed to relocate the Project in its August 2008 License Application to avoid any flow related effects in the Similkameen River below the Falls. The current design proposes siting the powerhouse such that the tailrace discharges directly below the Falls and circulates water to the toe of the Falls. This design-based mitigation feature benefits anadromous fish habitat, albeit at a cost to generation due to the reduced gross hydraulic head available. In the project configuration proposed in the District’s current license application, this loss of renewable energy has been partially offset by eliminating instream flow releases in an area of marginal fish habitat in the short reach between Enloe spillway and the Falls and instead creating additional high quality fish habitat in a side-channel of the river. So as presently configured, the proposed Project configuration represents a carefully developed balance of water resource uses and tradeoffs designed to protect critical environmental resources while harnessing the renewable energy potential at the existing dam.

Recent agency communications, received after submittal of the license application, related to the Section 401 Water Quality Certification for the Project have discussed requirements to meet State


narrative standards for aesthetics, as well as the maintenance of water quality for fisheries purposes in the bypass reach between the dam and the base of the Falls1.

At an April 1, 2010 meeting, the Washington Department of Ecology (Ecology) proposed a 10 cfs minimum instream flow in the short bypass reach between the dam and the Falls, increasing to 30 cfs between mid-July and mid-September, to protect both fish and aesthetic qualities. Although this minimum instream flow requirement would require revisiting the balance of the Project design and the proposed prevention, mitigation and enhancement measures (PM&Es), the District is prepared to discuss flows at these levels.

A paper submitted to Ecology in May 2010 titled Draft Analysis of Proposed Bypass Reach Instream Minimum Flow Requirements (Parametrix 2010) provided information on the implications of providing the 10/30 cfs instream flow scenario on (1) compliance with water quality criteria, (2) fish use in the bypass reach, (3) project design feasibility, (4) aesthetics, and (5) mitigation (PM&Es).

At meetings held in October 2010 among Ecology, WDFW, and the District, specific concerns related to implementation of the minimum instream flow in the bypass reach were discussed, including ramping rates, water quality, engineering design of the proposed instream flow release facilities, and the Parametrix 2010 paper. At that meeting, a series of agreements were made between Ecology, WDFW, and the District. These are as follows:

• There will be minimum instream flows, which will be 10 cfs year round increasing to 30 cfs from mid-July to mid-September.

• There will be a period of monitoring of DO and temperature. • If standards are not met, there will be an adaptive management process to determine

responses. • Those responses may include flow or other alternatives. • The determination of those responses (decision-making and implementation) will occur

within a timeframe acceptable to WDFW and specified by Ecology in the 401 cert. • Critical flow thresholds for bypass reach down-ramping requirements will be determined

from monitoring. • Bypass flow delivery (surface gate vs. piped from old penstock intake at 11’ below dam

crest) remains to be decided. • Tradeoffs affecting the downstream fishery will be considered in the determination of

these matters. • Future discussion will also revisit the proposed bypass off-site mitigation package (side

channel and flows). This Technical Memorandum includes information submitted in the Parametrix 2010 paper, as well as additional information regarding (1) a more detailed analysis to address the remaining questions about the potential for warming within the bypass reach at the proposed instream minimum flows, as well as (2) a description of design concepts proposed in conjunction with the 10 cfs and 30 cfs minimum instream flows, and (3) a description of fish surveys completed in the bypass reach in September 2010.

1 Section 173-201A-260 WAC states that “Aesthetic values must not be impaired by the presence of materials or their effects, excluding those of natural origin, which offend the senses of sight, smell, touch or taste.”


2.0 COMPLIANCE WITH WATER QUALITY CRITERIA Beginning with early consultation in 2005, questions and concerns surrounding potential Enloe Project effects on water quality have been focused on the primary importance of protecting water quality for the critical fisheries that use the Similkameen River downstream of Similkameen Falls. Agency, tribal, and other stakeholder consultation guided the completion of water quality studies focusing on the parameters of greatest concern: water temperature, dissolved oxygen (DO), total dissolved gas (TDG), and sediment contaminants. Findings from these studies were reported in the License Application as well as in a Technical Memorandum prepared specifically to address questions about compliance with water temperature standards. Elements of the project design, monitoring and adaptive management commitments, and other PM&Es were offered in the License Application to assure compliance with criteria for temperature, DO, and TDG.

At a May 7, 2010, meeting with Ecology and the Washington Department of Fish and Wildlife, Ecology indicated that the remaining analysis need was to address temperatures in the pool at the base of Enloe Dam during the critical warm season. This paper has been expanded since that meeting to address the potential for heating and compliance with water quality criteria both at this location within the bypass reach and downstream.

2.1 Hydrology To understand the potential for proposed minimum instream flows in the bypass reach to influence compliance with water quality criteria in the river downstream from the bypass reach, it is important to put the 10 cfs and 30 cfs flows in the perspective of the entire river flow. This means comparing how much of the river would flow through the bypass reach versus that diverted through the powerhouse.

Using daily average Similkameen River flow records from the Nighthawk gage, typical annual hydrographs were developed for high water years, average years, and low water years based on 80 years of data from 1929 through 2008 (Figure 1). The peak flow each year was during the snowmelt runoff season when peaks are primarily determined by the amount and timing of snowmelt. First, the years were sorted into the three groups based on the peak daily average flow for each year, with roughly the same number of years within each group. Then, the mean daily average flows were calculated for each day throughout the year, for each group of years, to construct the three typical hydrographs.

The Project is designed to divert up to 1,600 cfs through the powerhouse. Therefore, the current proposal for minimum instream flows would automatically be met by spill at the dam when total river flows exceed 1,610 cfs (or 1,630 cfs in the period mid-July to mid-September). Figures 2 through 4 show comparisons of the proposed minimum instream flows in the bypass reach with typical total river flows during the non-spill season in high water, average, and low water years. These figures illustrate that the minimum instream flows proposed for the bypass reach are a relatively small portion of the total river flows.


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2.2 Water Temperature The License Application and water temperature fact sheet concluded the following:

• Summer water temperatures in the lower Similkameen River naturally exceed the 17.5 ºC criterion and June water temperatures naturally exceed the 13.0 ºC spawning criterion that applies below the Falls;

• Monitoring results indicated that water temperatures do not increase significantly through the Project area and during part of the summer, the 7-DADMAX temperatures decrease through the project area due to the mixing of cool and warm inflows to the reservoir pool above the dam;

• Construction and operation of the Project are not expected to adversely impact compliance with water quality standards for temperature; and

• Water temperatures will be monitored to determine if Project operations are (1) leading to an increase in the 7-DADMAX compared to upstream conditions, and (2) complying with the criterion of no more than a 0.3 ºC water temperature increase in the waters protected for cold water fisheries.

The Project design with no bypass reach minimum instream flow requirements, would eliminate the potential for water temperature increases between the dam and below the Falls, even after river flows have receded from the snowmelt season. Concerns regarding temperature increases in the bypass reach are associated primarily with solar radiation, the effect of which is proportional to bypass flow surface area, and, to a lesser extent, heat transfer from warm air, longwave radiation and shallow water flowing over bedrock. Flow through the bypass reach is subject to solar radiation, and heat transfer, thus creating the potential for warming the river downstream from the Falls. Possible downstream affects of bypass flow temperature increases were evaluated in two ways as discussed below. With the proposed bypass reach instream minimum flows of 10 and 30 cfs, it is important to consider the risks of increasing downstream river temperatures.

2.2.1 River Temperatures Downstream From the Powerhouse Using the hydrology information presented above, a volumetric analysis was conducted to estimate, under the proposed instream minimum flow scenarios, how much the temperature would have to increase in the bypass reach to raise the downstream river temperature by 0.3 ºC, after mixing with powerhouse discharges. The lowest average daily flow between July 15 and September 15 was compared to the 30 cfs proposal for high flow, average flow, and low flow years (Table 1). Similarly, the lowest average daily flows for the year were compared to the 10 cfs proposal. Bypass reach instream minimum flows were calculated as a percentage of total river flows under these scenarios.

Assuming that the bypass reach flows will be well mixed with powerhouse discharges at the base of the falls, the temperature increase in the bypass reach required to raise river temperatures by 0.3 ºC was calculated using the volumetric proportions. As a simple example, if the total river flow was 300 cfs and the instream flow was 30 cfs, then the bypass reach would carry 10 percent of the total river flow and would have to be heated by 3.0 ºC to result in a 0.3 ºC increase in the river after mixing with the other 90 percent of the river discharged from the powerhouse.


Table 1. Estimated temperature increases that would need to occur in bypass reach in order to raise downstream Similkameen River temperature sufficiently to exceed the 0.3ºC criterion. 30 cfs Minimum Instream Flow 10 cfs Minimum Instream Flow

Low Flow

(cfs) Instream Flow (%)

Bypass Temperature Increase that would Lead to Exceedances

(ºC) Low Flow

(cfs) Instream Flow (%)

Bypass Temperature Increase that would Lead to Exceedances

(ºC) High Flow Year 702 4.3 7.0 635 1.6 19.0 Average Flow Year 530 5.8 5.3 513 1.9 15.4 Low Flow Year 460 6.5 4.6 452 2.2 13.6

Note: estimated temperature increases consider mixing with powerhouse discharge under proposed minimum instream flow scenarios.

The 10 cfs bypass reach instream minimum flow requirement does not appear to pose a serious threat to raise the downstream river temperature by 0.3 ºC. During a typical low flow year when the lowest average daily flow is as low as 452 cfs, the bypass reach water would have to be heated by 13.6 ºC to increase downstream river temperatures by 0.3 ºC (Table 1). If the upstream river temperature was 17.5 ºC (63.5 ºF), then this heating would result in a theoretical bypass water temperature of 31.1 ºC (88 ºF) at the Falls, which seems unlikely over a reach of approximately 340 feet (between the dam and the Falls). During an average or high flow year when more water would pass through the powerhouse and dilute the warmed bypass reach water, even more bypass water heating would be necessary to cause the same river temperature increase.

The proposed 30 cfs bypass reach instream minimum flow requirement would pose a greater risk to raise the river temperature by 0.3 ºC were there no physical limits to how fast bypass water temperature could actually rise given the finite amount of energy influx to the bypass stream, as further described in the temperature evaluation below. During a typical low flow year when the lowest average daily flow between mid-July and mid-September is as low as 460 cfs, the bypass reach water would have to be heated by 4.6 ºC to increase downstream river temperatures by 0.3 ºC (Table 1). If the upstream river temperature were 17.5 ºC (63.5 ºF), then this heating would result in a theoretical bypass water temperature of 22.1 ºC (72 ºF) at the Falls.

Structural modifications could potentially reduce the heating of minimum flows through the bypass reach and could provide circulation to avoid any potential for stratification of the plunge pool at the base of the dam, but could be criticized based on aesthetic perceptions. For example, minimum instream flows could be routed through a pipe and discharged to the plunge pool at the base of the dam. Piping the water around the dam would eliminate the solar radiation input and heat transfer from warm air to the thin sheet of flow that would otherwise fall over the dam; and circulation would still be provided in the plunge pool and flows over the natural bedrock to the Falls. This proposed Project design concept is discussed further in Section 3 of this document.

Another structural measure to reduce heating could be to cut a narrow channel through the bedrock to route flows between the plunge pool at the base of the dam to the Falls. There is an existing distinct channel that appears to be sufficiently deep that structural modifications may be able to focus on blocking distributary channels (particularly the 1905 channel excavated to serve the original Enloe hydro project) to keep flow in the thalweg. The purpose would be to reduce the


surface area of the bypass flow and thereby reduce radiant and convective energy influx through the water surface and reduce radiant heat transfer from the rock. However, the degree to which this measure would help is not clear because no survey data or other information exists that gives the width of the channel through this reach at 10 cfs or 30 cfs with the existing channel configuration. Again, structural modifications to the natural bedrock reach may have aesthetic effects. Given these concerns, water temperature monitoring during the nine-week 30 cfs flow period should be conducted to evaluate bypass flows in light of temperature effects, and consider measures if temperatures exceed the criterion in the river below the Falls.

To address the potential for heating in the pool at the base of the dam in response to Ecology’s request for an estimate of maximum daily temperature increases, rough shade modeling was conducted and hydraulic residence time (i.e. flushing time) was estimated for the proposed flow rates. The shade modeling approach that was performed to support the license application was applied to a mid-channel location 50 ft downstream from the base of Enloe Dam (i.e. approximately the middle of the pool). Apparently the orientation is such that the dam and surrounding topography do not provide prolonged shading of the pool in midsummer. On a clear day on July 15 the sun would first strike the pool at 7:00 am and the sun would set at 5:30 pm, for approximately 10.5 hours of direct sunshine. By September 15, the sun would first strike the pool at 7:30 am and sunset would occur at 3:15 pm, for a total of seven hours and 45 minutes of direct sun.

The hydraulic residence time analysis addresses the question of whether flows entering the pool at the base of the dam would likely flush through the area rapidly or be there for a long time and subjected to warming. The answer depends on the volume of the pool and the rate of flow into the pool. Only limited anecdotal information and no measurements exist to document the pool volume during low flows. Attempts to investigate the pool have been discouraged by strong current, poor visibility, and safety concerns.

During a snorkel survey to look for fish and habitat features between the Falls and Enloe Dam on September 14, 2006, Entrix recorded observations of pool dimensions (Table 2). Although most of the reach was not surveyed because of safety concerns, a mean depth estimate of 15 feet was recorded and on this day the river was flowing at approximately 239 cfs at the Nighthawk gage. Hydraulic residence time in the pool was calculated to be 13 minutes using these data, however, it is likely that 15 feet was an overestimate of the mean depth and the true hydraulic residence time was much less. Cody Fleece was the only person to enter the water during that survey, and he spent the time investigating potential fish passage channels above the Falls but did not venture very far into the pool due to currents (personal correspondence with Cody Fleece, May 7, 2010). He reported that visibility was never greater than 15 ft. During the September 15, 2010, snorkel survey in the bypass reach, WDFW took a few water depth measurements in the pool ranging from 8.1 to 15.2 feet, at approximately 600 cfs.

Dimensions of the pool at the base of Enloe Dam will be much smaller with the proposed instream minimum flows of 10 or 30 cfs. Table 2 presents two scenarios that likely bracket the range of pool dimensions that would occur at the proposed flows, with hydraulic residence time predicted for both 10 and 30 cfs under each scenario. Scenario #1 analyzes the hydraulic residence time if the bypass pool has average dimensions of 100 ft long, 75 ft wide, and 5 ft deep, during flows of 10 or 30 cfs. Scenario #2 analyzes the hydraulic residence time if the bypass pool has average dimensions of 80 ft long, 50 ft wide, and 2.5 ft deep, during flows of 10 or 30 cfs. During the critical warm season between July 15 and September 15 when the instream flow is proposed to be 30 cfs, the hydraulic residence time is predicted to be between six and 17 minutes. During the rest of the year, the pool would be flushed in approximately 17 to 63


minutes. These rapid flushing rates are not expected to leave water in the pool long enough to absorb enough heat to raise water temperatures by 0.3 ºC.

Table 2. Hydraulic residence time analysis for the pool at the base of Enloe Dam, using estimated pool dimensions.

Mean Length (ft)

Mean Wetted

Width (ft)

Mean Depth

(ft) Volume

(ft3) Flow (cfs)

Hydraulic Residence Time (sec)

Hydraulic Residence Time (min)

September 13, 2006

120 100 15 180,000 239 753 13

Bypass Flow Scenario #1 100 75 5 37,500 30 1250 21 100 75 5 37,500 10 3750 63

Bypass Flow Scenario #2

80 50 2.5 10,000 30 333 6 80 50 2.5 10,000 10 1000 17

2.2.2 Bypass Flow Temperatures After receiving comments on the May 2010 Draft Analysis of Proposed Bypass Reach Instream Minimum Flow Requirements (Parametrix 2010) the District had additional modeling performed to address the potential for heating within the bypass reach. This section summarizes water temperature rise calculations for proposed minimum instream flows over Enloe Dam and through the bypass reach pool at the base of the dam.

Heat gain calculations were initially performed using the assumption that bypass flows would flow over the entire width of the dam. The worst-case bypass temperature gain (e.g. hot, clear mid-summer afternoon) would be 0.6 to 0.7 ºC total heating at the dam face plus in the bypass reach pool, at the 30 cfs bypass flow proposed for July 15 through September 15. Total dam face and bypass reach pool temperature gain was calculated to be as high as 1.2 to 1.3 ºC using worst-case conditions and 10 cfs flow in late September.

Due to engineering concerns about the feasibility of regulating small flow increments over such a wide dam (see Section 3), and of the potential for use by coldwater fish, the heat gain calculations were repeated using the assumption of bypass discharges through a 10-ft wide gate rather than across the entire width of the dam. Table 3 summarizes the new bypass heat gain calculation results and show that discharging the bypass flows through a narrow gate effectively eliminates the temperature rise that would occur with flows passing over the entire dam in a thin sheet. If the bypass flows are routed to the bypass reach pool through a subsurface pipe intake rather than over the dam face, there would be no heating over the dam face and the cooler water drawn from below the surface would likely more than offset the temperature rise within the bypass reach pool (see section 3.5, Proposed Design Concept). Complete calculations and assumptions are available in electronic format from the District, on request.


Table 3. Bypass Flow Heat Gain Summary

Bypass Flow Temperature Rise (ºC) Bypass Reach Flow (cfs)

Pool Dimensions2

Dam Face with 10’ Gate

Bypass Reach Pool Total

30 Scenario #1 (75'W x 100'L x 5'D) 0.0 0.2 0.2

Scenario #2 (50'W x 80'L x 2.5'D) 0.0 0.1 0.1

10 Scenario #1 (75'W x 100'L x 5'D) 0.0 0.3 0.3

Scenario #2 (50'W x 80'L x 2.5'D) 0.0 0.2 0.2

The end result, using conservative assumptions, is that the bypass flow would only gain 0.1 to 0.3 ºC within the pool, depending on pool dimensions and bypass flow rate. The temperature gains summarized above are based on flow over a 10-feet wide crest gate, which would be installed at the northeast end of the dam. Earlier calculations, which assumed a wider sheet flow over the entire dam width, predicted that greater heating (0.5 ºC at 30 cfs or 1.0 ºC at 10 cfs over the dam face alone) would occur, primarily due to the greater surface area exposed to direct solar heating.

Alternatively, if flows over the dam face are not required and water is piped to the pool at the base of the dam, heating would be minimal. Design concepts needed for this configuration are discussed in Section 3 of this document. The FLA presented results from temperature profile measurements above the dam that showed thermal stratification and temperatures 0.5 ºC cooler than the surface at 3.2 meters depth. This information indicates that drawing cooler bypass flows from the existing penstock would likely more than offset heat gain within the bypass reach pool.

With the new bypass reach modeling results, the effect on Similkameen River water temperatures downstream from the powerhouse was revisited. The worst-case bypass temperature gain (e.g. 0.1 to 0.2 ºC total gain at 30 cfs) would result in only minor water temperature increases in the pool at the base of Similkameen Falls. If the worst-case bypass temperature gains both at the dam face and through the bypass reach coincided with the worst-case conditions for low flow (e.g. 300 cfs) and only one third of the tailrace discharge (100 cfs) circulated back to the base of the falls and mixed with the 30 cfs bypass flow, then the temperature increase at the base of the Falls would be less than 0.1 ºC and not measurable (Table 4). After full mixing with the tailrace discharge, the temperature increase in the Similkameen River would be even further reduced. Under the alternative with water piped to the toe of the dam the water temperature increase at the base of the Falls would also be less than 0.1 ºC and within the measurement error of standard monitoring equipment. If the water piped to the toe of the dam was drawn from depth through the existing penstock intake, then the net effect would likely be cooler water coming from the bypass reach during periods of temperature stratification above the dam. The effects of bypass flow heating on the pool at the base of the Falls would be even less under the 10 cfs minimum flow than during the 30 cfs minimum flow because only one-third as much water would be heated.

2 Scenarios described in Draft Analysis of Proposed Bypass Reach Minimum Instream Flow Requirements (Parametrix 2010).


Table 4. Potential Effect of Bypass Heat Gain on Similkameen River Temperatures Below the Falls. Temperature Rise (ºC) Bypass Flow Pool Below Falls

Bypass Reach Flow

(cfs) Pool Dimensions

Dam Face with 10’

Gate Bypass

Pool Only

Dam Face with 10’

Gate

Bypass Pool Only

30 Scenario #1 0.0 0.2 0.0 0.0 (75'W x 100'L x 5'D)

30 Scenario #2 0.0 0.1 0.0 0.0 50'W x 80'L x 2.5'D)

10 Scenario #1 0.0 0.3 0.0 0.0

(75'W x 100'L x 5'D)

10 Scenario #2 0.0 0.2 0.0 0.0 50'W x 80'L x 2.5'D)

The temperature increases described in this memorandum were calculated for the instantaneous maximum heat rise. Note that the increases in daily maximum temperatures averaged over seven days (7-DADMax), regulated under the surface water quality standards (Chapter 173-201A WAC), would be less than the instantaneous maxima calculated here.

2.2.2.1 Bypass Temperature Gains Previous calculations (Parametrix 2010) showed that the 30-cfs bypass flow (July 15 through September 15) temperatures would have to increase by 4.6 to 7 ºC (low to high river flow years) to increase the downriver temperature by 0.3 ºC, after mixing with powerhouse discharges. The rest of the year the 10-cfs bypass flow temperature gain would need to be 13.6 to 19 ºC to increase downriver temperatures by 0.3 ºC. The bypass temperature gain calculations presented below focus on the 30-cfs bypass flow scenarios because the lowest bypass flow temperature gain needed to increase the downstream temperature by 0.3 ºC occurs during the hottest months of the year when 30-cfs bypass flows are proposed.

Based on the evaluation of a worst-case scenario described below, 30-cfs bypass flow temperature gains are estimated as follows:

• 0.0 ºC over Enloe Dam.

• 0.2 ºC in the bypass pool, scenario #1 (75'W x 100'L x 5'D) from Parametrix (2010), for a total 0.2 ºC bypass flow temperature gain.

• 0.1 ºC in the bypass pool, scenario #2 (50'W x 80'L x 2.5'D) from Parametrix (2010), for a total 0.1 ºC bypass flow temperature gain.

Although bypass temperature gain is slightly higher for the 10 cfs scenarios, the higher gain is offset by lower bypass flow and there is less impact on the pool below the Falls.

The worst case scenario is essentially the bypass temperature gain from the crest of Enloe Dam to the crest of Similkameen Falls on a hot, clear mid-summer afternoon. This scenario is


represented by a number of bracketing assumptions intended to provide a conservative (high) estimate of possible increases in water temperature in the bypass reach. Key assumptions for planning the evaluation included:

• 99.2 ºF air temperature for the 30 cfs scenarios and 85.6 °F for the 10 cfs scenarios3.

• Full sun, no shade, light wind4 (greatest solar radiation).

• Flow over Enloe Dam, 10-feet wide crest gate.

Dark (e.g. black) bedrock was originally assumed on the premise that dark colors absorb more solar energy and emit more long wave radiation than lighter colors. However, no equations were found to describe either streambed heat flux or heat flux from terrain (e.g. rock canyon walls) along a stream. For reasons discussed below, heat flux (gain) from streambed conduction and long wave emissions from surrounding rocks were addressed by multiplying the net heat flux from other sources (e.g. solar, long wave, convective, evaporative) by a safety factor.

Bypass heat gain calculations were based primarily on heat flux equations for streams found in Mohseni et al (1999) and Bogan et al (2003). Detailed spreadsheet calculations, available on request from the District, show the equations and variables. Values for net insolation and atmospheric and water emissivity were obtained as follows:

• Net insolation: 4.8e1 kJ/m2/min; converted from National Renewable Energy Laboratory (NREL) maps showing 8 kWh/m2/day (July) and assuming 8 hours of insolation.

• Water emissivity: 0.97; value used in Bogan (2003), Mohseni (1999). Similar to values in Konda et al (1994), Salvaggio et al (2004).

• Atmospheric emissivity: 0.98, highest in Mohseni (1999), also high end of values noted in other literature reviewed for this study (<0.5 to 0.99 range).

Numerical values for variables were obtained from peer-reviewed literature, reference websites, this memorandum, or were assumed values as noted in the spreadsheet.

Net solar radiation at the water surface (net insolation) was calculated to be the largest single energy flux component. Atmospheric emissivity5, also related to the full sun assumption, and water surface emissivity taken together, were the second largest flux component; however, since atmospheric emissivity is an influx and water surface emissivity is an efflux, the net long wave energy flux is substantially less than net insolation. The net energy flux associated with air temperature is also small compared to net insolation. Convective heat influx and evaporative heat efflux are both directly proportional to the difference between air and water temperature, and were the only air-temperature-dependent variables described in Mohseni or Bogan. The calculated convective influx was similar in magnitude to the calculated evaporative efflux, thus tending to mitigate the effect of high air temperature. All flux terms are expressions of energy transfer per unit area per unit time. Overall, bypass temperature rise is proportional to surface area.

3 For the 30 cfs scenarios, the average over 10 years of the maximum rolling 7-day average daily maximum temperatures between July 15 and September 15. For the 10 cfs scenarios, the average over 10 years of the maximum rolling 7-day average daily maximum temperatures after September 15. 4 Although calm conditions were originally assumed, convective and evaporative heat fluxes are partly wind-driven so a 5 mph breeze was assumed in order to evaluate convection and evaporation. 5 Emissivity describes relative ability of a material to emit radiation energy from its surface.


Several papers and studies corroborate the relative importance of direct solar heating of streams. A quantitative graph and text in the Oregon Department of Environmental Quality (ODEQ) document The Scientific Basis for Oregon’s Stream Temperature Standard: Common Questions and Straight Answers (ODEQ 1997) suggests that solar flux is the dominant daytime energy source to typical streams. The figure, repeated here for discussion, is from Boyd (1996).

Figure 5. Typical stream energy balance, from Boyd (1996), figure repeated in ODEQ (1997).

Boyd studied a minimally shaded, small stream (4.2 to 4.5 feet wide, 9 to 11 inches deep) in Crook County, Oregon, collecting data in June 1996 on a clear day with little wind. The figure reflects the results of a simulation, which closely corroborated the field data. Figure 5 indicates that solar flux accounts for roughly 90% of the heat influx during mid-day. Brown (1969) reported similar results for a 2000-ft reach of Berry Creek, 10 miles north of Corvallis, Oregon. Figure 3 in Brown (1969) suggested a similar dominance of solar flux (i.e. solar is about 90% of mid-day influx). In another article Brown (1970) found that “…air temperature and the cooling effect of evaporation were much less important than solar radiation in controlling temperature on small, unshaded streams in the Oregon Coast Range. Solar radiation accounted for over 95% of the heat input during the midday period in midsummer."

Our detailed calculations suggest that net insolation might account for 65 to 74% of the bypass heat gain at Enloe Dam, similar to observations by Boyd and Brown for small Oregon streams. For Enloe, heat influx from the surroundings (e.g. long wave radiation from dark canyon rock) and streambed (e.g. conductive transfer from shallower rocks warmed by sunlight) presumably occurs to some extent. Although several sources mention streambed and possible other (undefined) heat fluxes, no equations were found to estimate these inputs. Boyd (1996) estimated bed conduction to be about 1/10th of net solar flux during midday, similar to other non-solar fluxes. An estimate for bed friction from Hannah et al (2004) was applied to the pool scenarios, resulting in a small (e.g. 7 to 10 kJ/m2/min) influx; however, the underlying assumptions for the friction estimate (actual stream bed, ordinary slope) are inconsistent with the configuration of Enloe Dam face. In order to account for possible long wave and stream bed (and friction for the dam face) heat influxes for which no equations were found, the net calculated heat influxes were multiplied by assumed factors of safety as follows:


• Enloe Dam face - 2.0, since the bed friction equation did not apply although there is friction.

• Bypass pool - 1.5, less than for Enloe Dam face because bed friction influx was calculated.

Heat gain calculations for the face of Enloe Dam were based on the assumption that the bypass flow will be discharged over a 10-foot wide crest gate. Temperature rise is directly proportional to flow surface area. This suggests that sheet flows should be avoided by either discharging through a pipe or keeping the width of the crest gate narrow to prevent heat gain.

Findings in the literature and calculated fluxes for the Enloe bypass flow suggest the assumed safety factors are conservative.

Key references that were available in portable data file format are included with the electronic distribution of this memo.

2.2.2.2 Bypass Pool Temperature Conclusions The key observations regarding bypass pool temperatures can be summarized as follows:

• Net insolation (direct solar radiation) is the primary factor driving bypass temperature rise.

• Net long wave heat influx was calculated, although atmospheric long wave emissions (influx) and water surface long wave emissions (efflux) tend to offset each other.

• Temperature rise increases moderately with air temperature, although evaporative efflux tends to offset convective influx.

• Temperature rise is proportional to flow surface area.

• Calculations show that the temperature gain within the bypass pool at the base of the dam would at no time exceed 0.3 ºC at the proposed instream minimum flow rates, using conservative assumptions and worst-case conditions (Table 3). Even during the lowest river flow conditions, and assuming that only one-third of the powerhouse discharge circulates up to the base of the Falls and mixes with bypass flows, the increase in temperature at the base of the Falls would not be measurable (Table 4).

• Previous modeling showed an additional temperature gain of 0.5 to 1.0 ºC could occur over the face of the dam if water was allowed to sheet-flow over the entire dam; however, this temperature rise could be avoided if (1) bypass flows are not required, (2) bypass flows are piped to the pool at the base of the dam, or (3) bypass flows are channeled over the dam through a 10-ft wide gate.

A final concern with the proposed bypass reach flows related to temperature is the likely buildup of ice that would occur during winter months. Depending on the configuration of the instream flow outlet works relative to rapid cooling of outflow, the proposed instream flow may cause large ice accumulations on the dam and in the broad, shallow bedrock area above the Falls. Consideration should be given to reducing flow requirement during periods when ice is observed to accumulate.


2.2.3 Dissolved Oxygen Although limited monitoring did not measure DO concentrations below 8.3 mg/L, the License Application concluded that DO likely drops below the 8.0 mg/L minimum criterion in the summer when the river is naturally very warm both upstream and downstream from the project.

A mid-August 1990 study found that sites downstream of the dam and Falls had DO concentrations approximately 1.0 mg/L higher than upstream DO due to significant aeration at the dam and Falls (HDR 1991). To offset the reduced aeration caused by passing water through the powerhouse, the powerhouse draft tubes will be equipped with aeration vents and operated to increase DO during critical periods, expected to occur during summer when water temperature is elevated. Tests of turbine aeration for dissolved oxygen enhancement, have shown that aeration efficiencies in the range of 10% to 50% are feasible which could also increase dissolved oxygen concentrations by more than 1.0 mg/l, depending on water temperature and degree of oxygen saturation in water upstream of the dam.

Using the same logic behind the volumetric analysis presented above for water temperature, a 1.0 mg/L increase in the 10 cfs or 30 cfs bypass flows would not have a measureable effect on the downstream river DO concentrations after mixing with the powerhouse discharge. Adaptively managing the draft tube aeration in the powerhouse to meet water quality criteria for DO will continue to be important.

The relatively short hydraulic residence times predicted in the water temperature analysis above are expected to result in adequate flushing of the pool at the base of the dam and prevent stagnation and oxygen depletion within the bypass reach. As described in Section 3.6, several engineering options are available to provide aeration of flows within the bypass reach if the bypass flows are piped to the plunge pool at the base of the dam rather than flowing over the dam.

2.2.4 Total Dissolved Gas As concluded in the License Application, TDG compliance is only a potential concern with the Project during high flows when most of the river will flow through the bypass reach because the powerhouse can only accommodate up to 1,600 cfs. As proposed the bypass reach minimum flow proposal would not have any effect on compliance with TDG criteria.

2.3 Fish Use in the Bypass Based on limited snorkel and habitat surveys, significant fish use is not expected during most of the year in the bypass reach. Fish use is expected to be extremely low in number if present at all during certain periods such as high flows that prevail in spring through early summer, and during low winter flows. When conditions are favorable, such as during late summer low flows, resident fish that access the plunge pool by going over the dam could potentially hold in the plunge pool area. During high spring and early summer flows, fish would likely have a very difficult time remaining in the area due to extremely high velocities. The sheer stress is expected to eliminate the vast majority of invertebrate habitat. During the winter, when flows are reduced, the area is expected to be covered in ice. Features such as anchor and frazzle ice would further reduce any potential for fish to use the area.

The approximately 370 feet long bypass reach area was surveyed in September 2006 by ENTRIX biologists to collect information for the preparation of the License Application. Although only a small portion of the reach was snorkeled because of safety concerns, no fish were observed. This 370 plus feet long reach consists of a plunge pool at the base of the dam, a bedrock chute and a run. The substrate consisted of flat bedrock substrate strewn with large boulders. Small substrate


particles occurred in sparse patches and margin habitat was minimal. The banks had no overhanging vegetation and no large woody debris was present at the time of the survey.

A snorkel survey and hook and line sampling was also completed in the bypass reach on September 15, 2010. Washington Department of Fish and Wildlife (WDFW) and Washington Department of Ecology (WDOE), ENVIRON and Colville Confederated Tribe fish biologists also sampled the bypass reach that day by snorkel survey sampling. Detailed results of the WDFW and WDOE sampling is provided in a separate report from the agencies. Observed habitat during the snorkeling survey was similar to the habitat previously reported (Okanogan PUD 2008). This includes primarily bedrock/boulder habitat throughout the bypass reach and little or no gravel deposits observed. The habitat dropped off very quickly from the shoreline making substrate observations restricted to the shore area. Fish that were observed or captured by hook and line included juvenile suckers (Catostomus spp), smallmouth bass (Micropterus dolomieui) sculpin (Cottus sp.), Northern pikeminnow (Ptychocheilus oregonensis) and rainbow trout (Oncorhynchus mykiss). No anadromous salmon or steelhead trout were observed/confirmed in the bypass reach.

3.0 PROJECT DESIGN

3.1 Objectives This section presents a discussion of engineering issues to be addressed in conceptual design of reservoir outlet works facilities to achieve proposed minimum instream flow releases.

Resource agencies and other stakeholders have proposed minimum instream flow releases between Enloe Dam and the base of Similkameen Falls for the following purposes:

1. Protection of fish habitat. 2. Aesthetics.

In order to meet these purposes consistent with various technical, environmental, operational and economic constraints the following additional objectives have been identified:

1. Outlet works to be able to meet minimum instream flow requirements over the full range of normal reservoir operations.

2. Provision to measure instream flow releases. 3. Outlet works to operate reliably unattended – i.e. not subject to blockage by trash or

sediment. 4. Provision to be made to make temporary instream flow releases while outlet works are

out of service. 5. Discharge to be accurately controlled to meet minimum instream flow requirements

which are expected to vary over the course of the water year. 6. Minimize environmental impacts of construction and operation. 7. Minimize overall cost of ownership.

3.2 Project Description The proposed hydropower generating facility would utilize the hydroelectric potential of the approximate 80 feet elevation change between the water surface of Enloe Reservoir and the surface of the plunge pool immediately downstream of Similkameen Falls.


Enloe Dam is a concrete gravity arch dam that was constructed in the period 1919-1923 as part of the second power development. The dam is 315 feet long with an arch radius of 200 feet and a maximum hydraulic height of 54 feet. The central overflow spillway crest that occupies most of the dam has a length of 276 feet. The spillway crest has provision for installing 5-foot high flashboards.

The original 3.2 –MW hydro powerhouse is located on the west bank of the river. The waterways have a total plan length of 900 feet. They are comprised of two gated intakes in the right dam abutment, two 750 feet long woodstave penstocks, two surge tanks, and a concrete powerhouse containing two horizontal-axis francis turbines, each mounted in cylindrical pressure case. Power generating facilities were decommissioned in 1958.

The new 9-MW power generation facilities would be constructed on the east bank of the river. The waterways would have a total plan length of 610 feet. A new 190 feet long intake channel would divert flow to a new concrete intake structure constructed in the left abutment of the dam. Two 170 feet long steel penstocks would serve the new concrete powerhouse. The powerhouse would contain two vertical tube-type Kaplan turbines and generators. A 180 feet long tailrace channel would return power flow from the powerhouse draft tube to the river. The proposal includes restoring the additional hydraulic head and reservoir storage capacity provided by the flashboards by substituting 5 foot high crest gates, which would provide greater operating flexibility.

The new power facilities will reduce stream flow in a short reach of river between the toe of the existing spillway to the base of the falls. This reach, which is about 370 feet long, is comprised of three short river segments:

1. An approximately 150 feet long by 180 feet wide stilling basin area downstream of a sloping apron at the toe of the spillway. The hydraulic length and width of this stilling basin area varies with flow over the spillway, and were estimated here from aerial photography at moderate flows. The stilling basin area includes a plunge pool that has been scoured in bedrock downstream of the toe of the spillway. The full extent of this pool is difficult to see due to turbulence in the stilling area, however Tables 2 through 4 above estimate the total dimensions of this pool at 10 and 30 cfs flows.

2. An approximately 190 feet long reach of shallow river channel scoured in bedrock between the stilling basin area and the top of the Falls.

3. Similkameen Falls –Approximately 30 feet of steep hydraulic chute from the top of the falls to the base which has been scoured through a bedrock terrace.

3.3 Design Considerations Providing instream flow releases at the dam to protect fish habitat in the spillway plunge pool would require changes to the design of proposed modifications to Enloe Dam and would reduce power generation. Depending on the magnitude of the instream flow releases and the change in flow available for power generation there may also need to be changes in turbine hydraulic capacity and operating characteristics. These issues are discussed in the following sections.

3.3.1 Dam Modifications The current Project configuration submitted to FERC in the license application includes restoring the flashboards on the dam by retrofitting crest gates. These gates restore the increase in water level and hydraulic head that was provided by the original flashboards on the spillway crest. In


addition they allow controlled releases from the reservoir to maintain outflow and downstream water levels during a plant outage.

These gates are not suitable for making continuous instream flow releases in the range of 10 to 30 cfs. Their long crest length would make it difficult to regulate outflow over the dam spillway at these low flows. Periodic accumulation of trash or ice against the face of the gates could also adversely affect their flow characteristics at such very low flows. These operational issues would result in either loss of energy if releases were too high or minimum instream flow release compliance issues if they were too low.

One solution would be to add an orifice type outlet with a small hydraulic gate sized for the desired flow range of 10 to 30 cfs with an integral flow gage to help regulate flow. This hydraulic gate could either be retrofitted to the dam crest at either abutment or retrofitted to the existing intake in the west abutment of the dam. Flow releases from this outlet could be discharged near the toe of the dam. Due to the outflow location relative to the toe of the stream channel, outflow would need to be channelized from the point of discharge at either abutment into the existing spillway plunge pool and stream channel.

If spillway aesthetics is an issue and there is a desire to see water on at least part of the spillway year round, then another option would be to create a separate 10 feet wide overflow flap gate at the east abutment of the dam for release of instream flow during spring through fall. As discussed earlier in this section, reliable operation of such a gate as a flow control device during winter may be adversely affected by river ice in which case a separate controlled orifice may be a more practical option during winter.

3.3.2 Power Facilities Increasing instream flow releases could also affect proposed power facilities including hydraulic turbine selection, turbine efficiency, and turbine operation. Generating efficiency of hydraulic turbines decrease with reduction of flow through the turbine, until a point at which the turbine must be shut down to avoid unstable operation or cavitation damage to the turbine runner. As currently proposed, the hydraulic turbines are designed to operate over the full range of flow. Instream flows in the range of 10 to 30 cfs could be accommodated without significantly affecting the present turbine selection, although they would reduce generation. Higher instream flow releases may trigger redesign of the turbine configuration. Post construction changes may require periodic shutdown of the generating units during low flow periods.

3.4 Design Criteria and Constraints

3.4.1 Minimum Flow Proposed minimum instream flows are listed in Table 5 below. Table 5. Proposed Minimum Instream Flow

Period Minimum Instream Flows (CFS) July 15 through September 15 30

Remainder of Year (September 16 through July 14) 10

3.4.2 Water Quality Instream flow releases should be made in a manner that does not adversely affect downstream water quality as follows:


Dissolved Oxygen – Previous studies have determined that flow over the existing spillway serves to increase dissolved oxygen in outflow from the reservoir by an estimated 1 mg/l. High dissolved oxygen levels benefit anadromous fish. Similar levels of aeration of instream flow releases are therefore desirable.

Water Temperature - Existing high water temperatures during summer in the lower Similkameen River have the potential to adversely affect habitat for cold water fish. Peak instantaneous water temperatures measured at Oroville typically reach 26 ºC (79 ºF) in July with peak daily mean temperatures reaching 24 ºC (75 ºF). Instream flow releases should be made so as to avoid additional temperature rise.

Suspended Solids - Enloe Reservoir is heavily silted. Bathymetric studies show that the reservoir is shallow in the upper reach where much of the larger bedload has accumulated and deeper near the dam due to the trapping of larger sediment upstream and scouring velocities that occur in the reach between the dam and a narrows in the river some 500 feet upstream. Outflow from the existing reservoir over the spillway, minimizes the entrainment of sediment from the reservoir in the outflow. Instream flow releases should be made to avoid blockage by sediment or any adverse affect on downstream fish habitat due to entrainment of sediment in outflow.

3.4.3 Reliability To assure compliance with instream flow requirements it is necessary to provide reliable outlet works that have the capability to automatically regulate instream flow unattended.

3.4.4 Fish The instream flow outlet should be designed to avoid an increase in fish mortality for downstream passage relative to current passage over the spillway.

3.5 Design Options The following design options have been identified:

1. Controlled flow releases over the proposed crest gates. 2. Separate flap or radial gate on spillway. 3. Low level outlet

The following sections present a description of each option and summarize potential advantages and disadvantages.

3.5.1 Controlled Flow Releases over the Proposed Crest Gates This option involves using one of the proposed crest gates on the spillway to control instream flow releases from the reservoir to the downstream reach. Since we presently propose to install two piers on the crest of the dam that would divide the gates into three separately controlled sections, it would be possible to use one section of the gates to regulate instream flow releases instead of the whole spillway crest.


3.5.1.1 Advantages:

1. Aesthetics. The flow would provide a thin sheet of water on about one third of the spillway chute.

2. Cost. Using the proposed crest gate obviates the need for additional outlet works to control instream flow releases.

3. Downstream Fish Passage. Downstream fish passage for fish entrained in the instream flow would be very similar to existing passage over the spillway.

3.5.1.2 Disadvantages:

1. Reliability. Due to their long crest length, and potential variable effects of wind, waves, trash, and accumulations of ice on overflow, it is unlikely that one of the three proposed crest gates could accurately and reliably provide controlled releases as low as 10 cfs.

2. Water Quality The potential increase in water temperature due to warming of discharge down the spillway chute is a major water quality concern which is discussed earlier in the memorandum.

3. Operation. This option should not be vulnerable to sediment blockage however it would be susceptible to blockage due to accumulation of ice and floating debris. Due to the lack of access from above for removal of trash or ice, the gates would need to be lowered to flush off debris. Similarly, the accumulation of ice pans or sheets against the gates would affect their ability to regulate very large flows with accuracy and reliability. The design of these types of gates provides for their crest level to be controlled remotely by air pressure. To provide a thin “sheeting” type flow, the gates would have to carefully monitored and adjusted.

4. Flow Measurement. Stream maintenance flows would also be very difficult to accurately measure for control and monitoring purposes.

Figure 6. Typical Obermeyer Gate Installation


3.5.2 Separate Flap or Radial Gate on Spillway This option involves building a separate flap or radial gate on the spillway crest with a pier to isolate it from the rest of the spillway. The gate would be located adjacent to a dam abutment and would be used to regulate minimum instream flow releases.

3.5.2.1 Advantages

1. Flow Control/Reliability. Better flow control than using larger crest gates. By making all the release through one gate section, the control of the elevation of water through the individual section becomes an easier task of maintaining a several inch tolerance on gate crest height verses a fraction of an inch tolerance if all gates are adjusted.

2. Water Quality. Less effect on temperature due to concentration of the outflow into a narrower stream.

3. Downstream Fish Passage. Downstream fish passage for fish entrained in the instream flow would be very similar to existing passage over the spillway.

3.5.2.2 Disadvantages

1. Cost. Constructing an additional instream flow gate and associated piers for instream flow releases would increase project costs.

2. Spillway Impact. The new gate would need to be constructed so as to not adversely affect overall spillway discharge capacity

3. Operation. Since a single gate would attract most or all of the floating debris, flow there is more of an issue of blockage by trash or large floating debris. As with the sheeting flow proposal, it is expected that sediment will not have an impact on operation or maintenance when spilling over all gate sections.

4. Flow Measurement. Using a single overshot gate would pose a technically difficult situation for monitoring and recording the projected flows downstream of the dam.

3.5.3 Controlled Releases through a Low Level Outlet This option involves making instream flow releases through an adjustable orifice. Flow would be controlled by a hydraulic valve rather than by an overflow weir.

Our proposal is to use one of the two existing penstock intakes. This concept has constructability advantages, cost advantages, certainty of flow, and the use of cooler water deeper in the reservoir to benefit aquatic life. A trashrack installed on the face of the intake structure would exclude debris, ice pans and adult fish from the intake. Small fish would pass through the intake and pipeline and are expected to have similar survivability as fish passing down the existing spillway.

As shown in Figure 7, this proposal uses the eastern penstock intake in the west abutment of the dam as its intake and conduit. The penstock would be capped with a welded blind flange at the downstream end and the new instream flow intake would be connected to the flange. After passing through a guard valve, mag flow meter and a control valve, the flow would be carried via a short pipe down the bank of the river to a point that is clear of the spillway flow. From there the flow would be discharged through a nozzle directed towards the plunge pool at the toe of the dam. The flow would be aerated as it plunges from the outlet of the pipe into the plunge pool.

Flow would be controlled by automated trim or shutoff valves. Due to the expected head pressure of the proposed release structure, the upstream surface water elevation would have an extremely small effect on the actual discharge water from this proposal. For example if the water


level upstream of the dam was to lower one foot, then the discharge of water from a fixed valve setting once made would be reduced less than 3 %.

3.5.3.1 Advantages

1. Flow Control/Reliability. This proposal of a gated discharge would provide accurate control of instream flow. Even if during an emergency, the upstream head pond of the reservoir was drawn down one foot below its regulated setting, this would have a small impact on instream flow releases.

2. Flow Measurement. The discharge water would be relatively easy to measure and document. In Figure 7, a magnetic flow meter is used to monitor the exact water flows. With proper placement of a magnetic style flow meter in the flow stream, a calibrated flow reading with error of less can +/- 0 .5 % and can be achieved. Since the flows can be accurately set and monitored, then compliance is relatively straightforward.

3. Temperature. There is an existing outlet available and abandoned penstock intake that can be utilized. This would provide a gated source of water at a lower and expected cooler position in the water column of the upstream forebay. The location of the proposed lower reservoir release would provide water at a water column up to 16 ft below the warmer surface temperatures of the forebay during the summer months. This is expected to almost always provide cooler water than a surface release using spill over the crest gates.

4. Downstream Fish Passage. This screened intake would reduce passage of adults downstream. Small fish that were able to get past the screen are expected to have low mortality in passing through the pipe and control valve and in being discharged into the pool below the spillway.

3.5.3.2 Disadvantages

1. Reliability. There is a potential for blockage by trash of the intake. Since the discharge would not be used during times when the dam is spilling it is expected that trash accumulation and removal will be a manageable issue. There is also potential for blockage by accumulation of sediment upstream of the intake due to the raising of the reservoir water surface using the proposed crest gates.

2. Condition of Existing Intake. The condition of existing outlet gates and penstock are unknown. The penstock is submerged up to 16 ft of head nominally but the lining and corrosion of the penstock and long term maintenance could be an issue. The ability to temporarily use the upstream gates to close off the one penstock would need to be determined by field inspection.

3. Operation. The control of the outlet would be physically on the other side of the river away from the powerhouse. Access to that side of the dam for manual changes is difficult. Power to the site if used for automating, or changes to the flow would increase any costs. Addition of improved power and communication would slightly increase the construction and long term maintenance costs.

3.6 Proposed Design Concept The recommended design concept involves adding a conventional orifice controlled instream flow outlet to one of two existing penstock intakes in the right abutment of the dam (Figure 6).

The primary advantage of this configuration is that the flow can be accurately controlled and measured to ensure that the required minimum releases are provided under varying streamflow conditions.


A low level outlet with a concentrated discharge would also minimize any temperature gain in water released from the reservoir as compared to a widely dispersed release of a thin film of surface water over the existing spillway.

The low level outlet will need to be protected with a trashrack to avoid having debris clog the intake or valves. There is some concern regarding future seasonal accumulation of sediment in front of the intake when the gates are raised and there is no spill at the dam. During the annual spill, it is expected that any accumulation of sediment upstream of the intake will be scoured and swept over the spillway.

Instream flow would be aerated to replace existing air entrainment provided by turbulence in flow down the existing spillway chute. Aeration of water in the bypass reach would be most important during late summer after spill has ceased and increases in water temperature and biological oxygen demand decrease dissolved oxygen concentrations. Aeration could be achieved by a number of different measures including:

1. Air entrainment in the discharge pipeline using a venturi or injection of compressed air.

2. Air entrainment in the area of impact and turbulence in the discharge jet where it impacts bedrock or the spillway plunge pool.

3. Air entrainment in the bypass reach using compressed air or a surface aerator.

The best option would be selected in detailed design of the instream flow facilities in consultation with resource agencies.

4.0 AESTHETICS Provision of flows to the bypass reach itself would improve aesthetics. If structural modifications provided flows through the bypass reach in a smaller, more focused channel, such as the narrow falls discussed above, the flows would be more visible to visitors who observe the dam and its related facilities on the east side of the Similkameen. Even without such modifications, the sight and sound of water moving through the bypass reach and cascading down the Falls would have a clear aesthetic benefit.

However, flows over the dam would contribute little to aesthetic values; particularly those associated with the sight and sound associated with water flow. This is because a 10/30 cfs flow would not amount to more than a thin sheet flow that would slide down the dam face and into the plunge pool. This amount of flow over the dam would contribute little to the visible or audible values at the site.

In the winter, when flow is lowest and freezing occurs (see discussion above), very few recreationists visit the area compared to other seasons. This lack of human use would greatly reduce the value of providing aesthetic flows during this season.

As discussed above, if structural modifications to reduce the heating of minimum flows through the bypass reach were to entail piping water to the Falls, visual aesthetic benefits would not be provided in the bypass reach (but would still occur through the Falls).


Figure 7. Proposed Instream Flow Outlet


5.0 ENVIRONMENTAL MITIGATION AND ENHANCEMENT Over the past five years the District has diligently carried out detailed engineering and environmental studies of the Enloe Project in consultation with Federal, State and Local resource agencies, Native American tribes and other stakeholders. Through that process, a proposed program of Environmental Protection, Mitigation and Enhancement Measures (PM&E) has been carefully developed to restore this renewable energy source for the benefit of the Districts power customers while protecting and enhancing environmental resources.

The proposed project configuration submitted in the license application addresses protection of water quality and fish habitat downstream of the dam by a carefully developed environmental mitigation and enhancement plan that would result in a net benefit to fish habitat and water quality. As part of this plan, creation of additional high quality habitat in a side channel of the river was proposed in lieu of minimum instream flow releases in the short bypass reach between the spillway and the pool at the base of the falls which is the point where flow diverted through the powerhouse rejoins the river.

Changing the PM&E program to include minimum instream flow releases in the bypass reach to acquire certification under Section 401 of the Clean Water Act increases project costs and reduces renewable energy generation. While the small loss in generation cannot be avoided, the increase in construction and ongoing operating costs could be partially offset by downsizing the proposed side channel fish habitat mitigation proposal. Substantial resources that have already been expended on environmental studies, planning and permitting of this mitigation proposal cannot be recovered. However, in light of some uncertainty regarding issues related to setting minimum instream flows due to potential water temperature impacts and potential stranding of fish in the bypass reach, the District believes that it would be prudent to keep the side channel fish habitat enhancement measure in the PM&E package as part of a contingency plan to ensure that the project is in compliance with the State’s water quality standards. Surplus environmental benefits resulting from having both minimum instream flows and creating additional fish habitat could be considered to either be enhancement or insurance against uncertainty.

6.0 CONCLUSION This memorandum provides information on the implications of providing the 10/30 cfs instream flow scenario and ramping for the Enloe bypass reach between the dam and the Falls on (1) compliance with water quality criteria, (2) fish use in the bypass reach, (3) project design feasibility, (4) aesthetics, and (5) mitigation (PM&Es).

The key observations regarding bypass water quality can be summarized as follows:

• Net insolation (direct solar radiation) is the primary factor driving bypass temperature rise.

• Net long wave heat influx was calculated, although atmospheric long wave emissions (influx) and water surface long wave emissions (efflux) tend to offset each other.

• Temperature rise increases moderately with air temperature, although evaporative efflux tends to offset convective influx.

• Temperature rise is proportional to flow surface area. • Calculations show that the temperature gain within the bypass pool at the base of the dam

would at no time exceed 0.3 ºC at the proposed instream minimum flow rates, using conservative assumptions and worst-case conditions (Table 3). Even during the lowest river flow conditions, and assuming that only one-third of the powerhouse discharge


circulates up to the base of the Falls and mixes with bypass flows, the increase in temperature at the base of the Falls would not be measurable (Table 4).

• Previous modeling showed an additional temperature gain of 0.5 to 1.0 ºC could occur over the face of the dam if water was allowed to sheet-flow over the entire dam; however, this temperature rise could be avoided if (1) bypass flows are not required, (2) bypass flows are piped to the pool at the base of the dam, or (3) bypass flows are channeled over the dam through a 10-ft wide gate.

• The relatively short hydraulic residence times predicted in the water temperature analysis above are expected to result in adequate flushing of the pool at the base of the dam and prevent stagnation and oxygen depletion within the bypass reach.

• Several engineering options are available to provide aeration of flows within the bypass reach if the bypass flows are piped to the plunge pool at the base of the dam rather than flowing over the dam.

• TDG compliance is only a potential concern with the Project during high flows when most of the river will flow through the bypass reach because the powerhouse can only accommodate up to 1,600 cfs.

Limited fish and habitat surveys indicate several fish species (suckers, bass, sculpin, Northern pike minnow and rainbow trout) use the bypass reach during reduced flows as indicated by a September survey. Fish use is expected to be low in number, if present at all, during certain periods such as high flows that prevail in spring through early summer, and during low winter flows with ice conditions.

Engineering design options for providing the bypass reach water includes 1.) controlled flow releases over the proposed crest gates, 2) separate flap or radial gate on spillway and 3.) low level outlet. The recommended design concept involves adding a conventional orifice controlled instream flow outlet to one of two existing penstock intakes in the right abutment of the dam. The primary advantage of this configuration is that the flow can be accurately controlled and measured to ensure that the required minimum releases are provided under varying streamflow conditions. A low level outlet with a concentrated discharge would also minimize any temperature gain in water released from the reservoir as compared to a widely dispersed release of a thin film of surface water over the existing spillway. Provision of flows to the bypass reach would improve aesthetics, including flows over the Falls.

Environmental mitigation and enhancement has been developed and submitted in the Final License Application to mitigate for no flows in the bypass reach. The mitigation would result in a net benefit to fish habitat and water quality through creation of additional high quality habitat in a side channel of the river. Given the uncertainty regarding issues related to setting minimum instream flow, the District believes that it would be prudent to keep the side channel fish habitat enhancement measure as part of a contingency plan to ensure that the project is in compliance with the State’s water quality standards.

A series of preliminary agreements made between Ecology, WDFW, and the District are as follows.

• There will be instream flows, which will be 10 cfs year round with 30 cfs mid-July to mid-September.

• There will be a period of monitoring of DO and temperature. • If standards are not met, there will be an adaptive management process to determine

responses. • Those responses may include flow or other alternatives.


• The determination of those responses (decision-making and implementation) will occur within a timeframe acceptable to WDFW and specified by Ecology in the 401 cert.

• Critical flow thresholds for bypass reach down-ramping requirements will be determined from monitoring.

• Bypass flow delivery (surface gate vs. piped from old penstock intake at 11’ below dam crest) remains to be decided.

• Tradeoffs affecting the downstream fishery will be considered in the determination of these matters.

• Future discussion will also revisit the bypass existing mitigation package (side channel and flows).


7.0 REFERENCES Bogan, T., O. Mohseni and H.G. Stefan. Stream Temperature-Equilibrium Temperature

Relationship. Water Resources Research, Vol. 39, No. 9, doi:10.1029/2003WR0002034, September, 2003.

Boyd, M. S. 1996. Stream segment temperature change as a measure of thermal health. Proceedings from James A. Vomocil Water Quality Conference.

Brown, G. W. 1969. Predicting temperatures of small streams. Water Resource. Res. 5(1): 68-75.

Brown, G. W. 1970. Predicting the effects of clear cutting on stream temperature. Journal of Soil and Water Conservation. 25: 11-13.

Hannah, D.M., I. Malcolm, C. Soulsby and A. Youngson. 2004. Heat Exchanges And Temperatures Within A Salmon Spawning Stream In The Cairngorms, Scotland: Seasonal And Sub-Seasonal Dynamics. River Res. Applic. 20:635-652. Published online 30 June 2004 in Wiley InterScience.

Konda, M., N. Imasato, K. Nishi and T. Toda . 1994. Measurement of the Sea Surface Emissivity. Journal of Oceanography, Vol. 50, pp. 17 to 30. 1994.

Mohseni, O., H.G. Stefan. 1999. Stream Temperature/Air Temperature Relationship: A Physical Interpretation. Journal of Hydrology 218 (1999) 128-141.

ODEQ. 1997. The Scientific Basis for Oregon’s Stream Temperature Standard: Common Questions and Straight Answers Prepared By Matthew Boyd and Debra Sturdevant, Oregon Department of Environmental Quality, August, 1997.

Parametrix. 2010. Draft Analysis Of Proposed Bypass Reach Instream Minimum Flow Requirements, Enloe Hydroelectric Project. Parametrix, Bellevue, Washington. (draft memo in preparation).

Salvaggio, C. and D. Miller. 2004. Temporal Variations In The Apparent Emissivity Of Various Materials. Algorithms And Technologies For Multispectral, Hyperspectral, And Ultraspectral Imagery X, edited by Sylvia S. Shen, Paul E. Lewis, Proceedings of SPIE Vol. 5425 (SPIE, Bellingham, WA, 2004) ·0277-786X/04 10.1117/12.546321.

WEBSITES UTILIZED

http://www.engineeringtoolbox.com

http://www.usairnet.com/weather/maps/current/washington/barometric-pressure/

http://www.nrel.gov/

http://www.csgnetwork.com/vaporpressurecalc.html

http://www.vcrlter.virginia.edu/~bph/AW_Book_Spring_96/AW_Book_21.html

http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/

Washington Department of Fish and Wildlife Report on September 15, 2010

Snorkel Survey

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