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Buckmire Slough Surface Water Hydraulic Modeling Lower Columbia River Estuary near Vancouver, WA

July 24, 2015 Version: Draft of Alternative 1 Condition

CENWP EC-HY i Buckmire Slough Surface Water Hydraulic Modeling July 24, 2015

Table of Contents

1.0 INTRODUCTION ............................................................................................................................ 1

1.1 Purpose .......................................................................................................................................... 1

1.2 Background ................................................................................................................................... 1

1.3 Authority ....................................................................................................................................... 1

2.0 STUDY OBJECTIVES ..................................................................................................................... 4

2.1 Approach ....................................................................................................................................... 4

2.2 Basic Study Assumptions.............................................................................................................. 4

3.0 LCR MODEL MODIFICATIONS ................................................................................................... 5

3.1 Hydrology ..................................................................................................................................... 5

3.2 Hydraulics ..................................................................................................................................... 6

3.3 Calibration ..................................................................................................................................... 6

4.0 EXISTING CONDITIONS MODELING....................................................................................... 10

4.1 Description of Models ................................................................................................................. 10

4.1.1 Additional 1-D Elements .................................................................................................... 11

4.1.2 Additional 2-D Elements .................................................................................................... 13

4.2 Assumptions ................................................................................................................................ 14

4.3 Conditions Modeled .................................................................................................................... 15

4.4 Results ......................................................................................................................................... 17

5.0 ALTERNATIVE 1 CONDITIONS MODELING .......................................................................... 26

5.1 Description of Models ................................................................................................................. 26

5.1.1 1-D Elements Modifications ............................................................................................... 26

5.1.2 2-D Elements Modifications ............................................................................................... 30

5.2 Assumptions ................................................................................................................................ 31

5.3 Results of Long Term Run .......................................................................................................... 32

5.3.1 Water Levels and Site Elevation Gradients ........................................................................ 33

5.3.2 Site Water Balance .............................................................................................................. 38

5.3.3 Velocity ............................................................................................................................... 41

5.4 Alternative 1 Deliverables .......................................................................................................... 42

6.0 COMPARISON OF BEFORE AND AFTER PROJECT ............................................................... 43

6.1 Points of Comparison .................................................................................................................. 46

CENWP EC-HY ii Buckmire Slough Surface Water Hydraulic Modeling July 24, 2015

6.2 Comparison of Depth Grids ........................................................................................................ 46

7.0 CONCLUSIONS & RECOMMENDATIONS ............................................................................... 46

7.1 Identified Risk Factors ................................................................................................................ 46

7.1.1 Flood Risk ........................................................................................................................... 46

7.1.2 Agricultural/Infrastructure Risk .......................................................................................... 46

7.2 Other Considerations................................................................................................................... 46

8.0 REFERENCES .............................................................................................................................. 47

APPENDIX A – To be completed at end of study

APPENDIX B – DQC CERTIFICATION – To be included at end of study

Abbreviations Used in this Report

ACE – Annual Chance Exceedance BPA – Bonneville Power Administration CREST – Columbia River Estuary Study Taskforce cfs (kcfs) – cubic feet per second (thousand cubic feet per second) DEM – Digital Elevation Model EC-HY or CENWP-EC-HY – River and Hydrologic Engineering Section, USACE Portland District (engineering section responsible for this study) FEMA – Federal Emergency Management Agency fps – feet per second HGL – hydraulic grade line LCR – Lower Columbia River LCEP – Lower Columbia Estuary Partnership LiDAR – Light Detection and Ranging NOAA – National Oceanic and Atmospheric Administration RAS or HEC-RAS – River Analysis System modeling program USACE – US Army Corps of Engineers USGS – US Geological Survey WDFW – Washington Department of Fish and Wildlife

CENWP EC-HY iii Buckmire Slough Surface Water Hydraulic Modeling July 24, 2015

List of Tables

No table of figures entries found. – To be completed at end of study.

List of Figures

Figure 1: Otak Phase 1 30% plan and Phase 2 conceptual plan overview .................................................... 2

Figure 2: Overview of Buckmire Slough and Surrounding Area, with added RAS basins (blue) and reaches

(red) ............................................................................................................................................................... 3

Figure 3: Tributary area additions (in red) to the LCR model ....................................................................... 5

Figure 4: Clip location of LCR RAS model ...................................................................................................... 6

Figure 5: Calibration of February 1996 at Vancouver, WA ........................................................................... 7

Figure 6: Calibration of January 2009 at St. Helens, OR ............................................................................... 8

Figure 7: Calibration of February 1996 ......................................................................................................... 9

Figure 8: Calibration of June 1999 ................................................................................................................ 9

Figure 9: Calibration of January 2009 ......................................................................................................... 10

Figure 10: Buckmire Slough in LCR RAS model ........................................................................................... 12

Figure 11: Buckmire Slough in modified model .......................................................................................... 12

Figure 12: Detail of 2‐D flow area mesh with underlying terrain ............................................................... 13

Figure 13: 2‐D flow areas and their positions within the RAS model ......................................................... 14

Figure 14: Modeled Flow and Stage at Vancouver for modeled time periods ........................................... 15

Figure 15: Modeled Flow and Stage at St. Helens for modeled time periods ............................................ 16

Figure 16: Site overview with profile (pink) and hydrograph (yellow) locations ........................................ 17

Figure 17: Modeled Columbia River profile, St. Helens, OR to the Willamette River ................................. 18

Figure 18: Modeled Lake River profile from the Columbia River to Vancouver Lake ................................. 18

Figure 19: Modeled Stage at Caterpillar Slough and flow into Hart and McBride Lakes complex ............. 19

Figure 20: Stage in Hart and McBride Lake complex and net flow to Pencil Lake and Rookery Complex . 20

Figure 21: Flow and Stage upstream of most downstream earthen barrier (removed in Otak plans) in

Buckmire Slough ......................................................................................................................................... 20

Figure 22: Stage and inflow of Shillapoo Lake ............................................................................................ 21

Figure 23: Stage and net inflow of Vancouver Lake ................................................................................... 22

Figure 24: Maximum depth for February 1996 ........................................................................................... 23

Figure 25: Maximum depth for June 1999 .................................................................................................. 23

Figure 26: Maximum depth for January 2009 ............................................................................................. 24

Figure 27: 2 hours after start of levee overtop during February 1996 ....................................................... 25

Figure 28: Alternative 1 Model Modifications ............................................................................................ 27

Figure 29: Weir connection from Caterpillar to Hart‐McBride in effective conditions. ............................. 28

Figure 30: North breach connection from Caterpillar to Hart‐McBride in Alternative 1. .......................... 28

Figure 31: Buckmire Slough profile for Alternative 1 with adjustments for model stability (Lake River

connection on the left). .............................................................................................................................. 29

Figure 32: Buckmire Slough profile for the Existing Conditions (Lake River connection on the left). ........ 30

Figure 33: North breach with channel cut and 2‐D mesh modifications. ................................................... 31

CENWP EC-HY iv Buckmire Slough Surface Water Hydraulic Modeling July 24, 2015

Figure 34: Flow and stage at Vancouver, WA for 180‐day run. .................................................................. 32

Figure 35: Surface water elevation and water balance locations. .............................................................. 34

Figure 36: Comparison of Mathews North to the North Breach ................................................................ 35

Figure 37: The Buckmire Connection as compared to the North Breach and Mathews South. ................. 36

Figure 38: Lake River connection as compared to the North Breach and Buckmire Connection. ............. 36

Figure 39: Pencil split as compared to the South Breach. .......................................................................... 37

Figure 40: Bass Hart and comparison to the breaches. .............................................................................. 38

Figure 41: Tidal water exchange for normal tides. ..................................................................................... 39

Figure 42: Water Balance for the freshet. .................................................................................................. 40

Figure 43: Weekly net flow for 180‐day simulation. ................................................................................... 40

Figure 44: Velocity in Buckmire Slough for the 180‐day run. ..................................................................... 42

Figure 45: Columbia River profile in vicinity of site and difference to existing conditions ........................ 43

Figure 46: Lake River profile and comparison to existing conditions. ........................................................ 44

Figure 47: Maximum depth grid for Alternative 1 during the January 2009 high water event. ................. 45

CENWP EC-HY 1 Buckmire Slough Surface Water Hydraulic Modeling July 24, 2015

1.0 INTRODUCTION The Buckmire Slough project, as shown in Figure 1, proposes to reconnect several hundred acres of historic bar and scroll floodplain to the Columbia River and Lake River. The project is envisioned in two phases that are necessarily connected to form the complete project. Phase 1 led by CREST will reconnect Buckmire Slough to Lake River to the east with removal of barriers and minor earthmoving. Phase 2 led by WDFW will reconnect much of the existing Shillapoo South Unit to the Columbia River to the west by breaching an existing levee in two locations and removing several interior water control structures. Also proposed during phase 2 is connection to the phase 1 project by the removal of two significant barriers along Buckmire Slough. The complete project will allow Columbia waters to inundate the landscape and flow into Lake River through the newly reconnected floodplain. These actions will significantly alter the hydrology within the restoration area. Unless otherwise noted, all elevations in this report are in NAVD88. 1.1 Purpose The purpose of this study is to assess the change in flood and agricultural/infrastructure risk to the lands adjacent to the Buckmire Slough area with a reconnection to the Columbia River and associated improvements. This includes areas such as Shillapoo Lake, Vancouver Lake, Lake River, Caterpillar Slough and adjacent lands within the existing levee protected area to the southwest of Buckmire Slough. 1.2 Background Four embankments have been constructed across Buckmire Slough since it was disconnected from the Columbia River. The resulting areas, while connected by culverts, have poor water quality and fish access to these areas is nonexistent. Two of these are to be removed and one pedestrian bridge will be installed during Phase 1 under 30% plans prepared by Otak (see the technical memorandum dated February 27, 2014). The remaining two barriers, a service road and state highway 501 would be replaced with bridges during Phase 2. Phase 2 construction would breach the levee in three places, construct a setback levee, remove many culverts from the ‘finger lakes’ and increase connectivity between these lakes with constructed channels. Figure 1 shows an overview of the proposed activities. Figure 2 shows the general layout of the site with areas labeled to facilitate discussion. 1.3 Authority This USACE study is being conducted under contract with the BPA. All work is being done within the River and Hydrologic Engineering Section of Portland District (CENWP-EC-HY).


Figure 1: Otak Phase 1 30% plan and Phase 2 conceptual plan overview


Figure 2: Overview of Buckmire Slough and Surrounding Area, with added RAS basins (blue) and reaches (red)


2.0 STUDY OBJECTIVES Focus of this study is to inform on the two primary risk categories identified during the August 18, 2014 Buckmire technical workshop. These two risk categories are: Flood risk management and Agricultural/Infrastructure risks due to changed hydrologic regime in the restored area. In general, a focus on the change in water surface elevation on and adjacent to the site will be used to quantify risks due to the restoration activities. An “existing condition” will be analyzed to assess flood elevations in the region with existing landscape features. A “with-project” condition will then be analyzed and compared with the “existing condition” to demonstrate changes in flood water surface elevations due to the project. 2.1 Approach This study assumes that surface water modeling is sufficient to characterize the changes in risk to the areas in and around the proposed project. Three selected events – a large flood, a typical winter storm and a typical freshet (upper Columbia River basin summer snowmelt) – are assumed to representative of the risk changes if modeled with existing conditions and a proposed alternative. These representative storms are selected as February 1996, June 1999 and January 2009. 1996 is a well documented flood that many people have direct experience with in Oregon and southwest Washington. 2009 and 1999 peak at about the 50% Annual Chance Exceedance (ACE) in the Lower Columbia River (LCR) under the winter and freshet flow regimes, respectively. Both have fairly representative shapes for winter (relatively fast rise and fall) and summer (high sustained flow). 2.2 Basic Study Assumptions The following are assumptions and exclusions of this study and its associated modeling:

Details of existing pumping or water control structure operations are not required to establish existing conditions related to the two identified risk categories.

Agricultural/Infrastructure risks due to changed hydrologic regime in the restored area can be addressed by changes in surface water elevations within the project footprint. This study does not perform any type of groundwater modeling.

Flood risk will be addressed with modeling of the 1996 event and comparison of maximum water surface elevations between the existing and alternative condition within the domain. Modeling specific to address FEMA National Floodplain Insurance Program implications is not within the scope of this study.

Where data was not available, best judgment was made. This is generally adequate for the planning level model development and analysis in this flood study.

This study adapts a proposed alternative to compare the two risks noted here. Detailed modeling to refine the proposed conditions is not included in this study and it is assumed that the design of each project feature will be done at a later date.

Use of beta model software is acceptable for planning purposes – a release version of HEC-RAS 5.0 was not available at the time of publication. If the release version of


HEC-RAS 5.0 occurs before the end of the study, the release version will be used for final model runs.

This study does not attempt to quantify ecosystem function. 3.0 LCR MODEL MODIFICATIONS The existing USACE HEC-RAS model of the Columbia River below Bonneville dam, developed for the Columbia River Treaty to simulate flood flows, has been modified to provide additional detail in the project area and to better simulate a wider range of flows. 3.1 Hydrology Previous iterations of the LCR RAS model have been primarily concerned with flows out of Bonneville dam and the large rivers (e.g. the Willamette and Cowlitz) as the main contributors of inflow. The majority of the area not previously accounted for consists of smaller, comparatively flashy basins in the LCR and a couple of basins between The Dalles Dam and Bonneville. In total this unaccounted area is 2,950 square miles (Figure 3 shows these in red), a small fraction of the approximately 240,000 square miles the Columbia River drains above the dam.

Figure 3: Tributary area additions (in red) to the LCR model

However, since these basins have a short time of concentration and flow directly into the Columbia, they are important in winter storms such as the February 1996 event, which has added about 200 kcfs of inflow with the new hydrology. EC-HY developed regression relationships for each HUC10 and added these newly calculated flows into the LCR RAS model. A complete


methodology and RAS model inputs can be found in the report “Lower Columbia River RAS model hydrology” (dated January 16, 2015). 3.2 Hydraulics The furthest downstream long term dataset in the LCR is the NOAA Astoria gage (9439040), located at Tongue Point, at river mile 18. It is not necessary to produce information about the river downstream of Tongue Point for this study and shifting the boundary to the ocean, as is the case in many versions of the LCR RAS model, introduces needless uncertainty and computational complexity. Therefore the LCR RAS model has been clipped to the NOAA gage, just downstream of where Prairie Channel rejoins the main Columbia River channel. Figure 4 shows the location of the new downstream end within the complete geometry used for this study.

Figure 4: Clip location of LCR RAS model

3.3 Calibration One of the motivations to change the hydrology of the LCR RAS model was an inability to obtain good calibration throughout the Columbia River flow regime, from riverine flooding (both winter and freshet) to lower flow tidal time periods. Either the model would calibrate to peak winter events or the freshet and the tidal cycle. If a calibration was done to the tide cycle and the freshet, winter storms would be low under peak flow. Roughing the model and calibrating to these peaks would in turn raise the tidal cycle and the freshet. Improving the hydrology (i.e. adding these LCR tributary areas) primarily added flow to winter events. The additional flow

LCR model clipped here.


increased winter peak stages and moved the peak flow forward in time. Roughness factors for the model were generally reduced to better calibrate low flow periods where tidal fluctuation dominates the hydrograph. Figure 5 shows the difference these additional flows make at Vancouver, WA for the February 1996 event.

Figure 5: Calibration of February 1996 at Vancouver, WA

Black – Observed Data Blue – Stage with Previous Hydrology Red – Stage with New Hydrology Dark Green – Flow with Previous Hydrology Light Green – Flow with New Hydrology

Model warm up period


Figure 6: Calibration of January 2009 at St. Helens, OR

Figure 6 shows model calibration at St. Helens, OR for January 2009. The peak stage and timing is very good, with the rising limb tidal cycle very close to observed data. The falling limb is above observed data, but mimics the shape quite well. Figure 7, Figure 8 and Figure 9 show observed stage compared with modeled stage for February 1996, June 1999 and January 2009. A point below the 1:1 line indicates that the model is below the observed stage for that time step; a point above the line indicates is model is high relative to observed stage. Each chart shows those time series that are available for NOAA and USGS gages in the LCR. Before 2003, the St. Helens, Longview and Skamokawa gages are only available as tidal predictions. As such, February 1996 and June 1999 exclude these locations. The altered model calibrates quite well over a wide range of conditions. The calibrated flow events are tight to the 1:1 line, with a fairly even distribution above and below. One item of note: the outliers forming a line pointing downward are a function of a warm-up period for the model. They should be disregarded when assessing calibration, but are included for completeness. This warm-up period can also be seen in Figure 5 on the left.


Figure 7: Calibration of February 1996

Figure 8: Calibration of June 1999

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Figure 9: Calibration of January 2009

4.0 EXISTING CONDITIONS MODELING The modified LCR RAS model simulates the Lower Columbia River as a whole very well. As it is a model mostly concerned with flood risk across the entire river as a whole, it does not show the detail necessary for this study in any particular area. EC-HY has added detail to the project area including integrating new 2-D flow capabilities of HEC-RAS 5.0 beta into the model in order to accurately model the existing conditions and effects of proposed restoration actions specific to the Buckmire Slough project. The following subsections describe development project specific model attributes for existing conditions modeling beyond the general model calibration described above. 4.1 Description of Models The LCR RAS model simulates Vancouver Lake and Shillapoo Lake as two large one dimensional storage areas. Buckmire Slough itself does not exist in the model and is part of the Vancouver Lake storage area. A new Buckmire Slough reach has been added to the model. 2-D flow areas and additional storage areas have replaced the single feature between the Columbia River and Buckmire Slough in the LCR RAS models. Figure 10 and Figure 11 show the model differences in this area. Note that the black areas in the center of Figure 11 are the 2-D flow areas with mesh cells so dense that they appear solid black; Buckmire Slough is the reach between the two storage areas.

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The base terrain for these modifications is the Lower Columbia River Digital Elevation Model (DEM), clipped to the domain surrounding the project area. This includes the Columbia River adjacent to the project, Caterpillar Slough, the leveed area containing the finger lakes and Shillapoo Lake, Buckmire Slough, the upstream end of Lake River and a portion of Vancouver Lake adjacent to Buckmire Slough. LCEP provided the clipped base terrain with bathymetry in the areas that it is available (noted below).

4.1.1 Additional 1-D Elements Buckmire Slough is the main addition to the 1-D elements of the model. 73 cross sections along with 8 lateral structures and 5 inline structures, representing each of the four barriers across the Slough and the connection to Lake River. The quality of the input data is somewhat variable for this area. The available bathymetry for the interior lakes and Buckmire Slough from culvert connecting East Rookery (RAS section 2.423) to the confluence with Lake River – collected by WDFW (interior lakes) and Otak (Buckmire Slough) – is integrated into the model. Upstream of this connection, the engineer estimated a trapezoidal section to substitute for the lack of bathymetry. A small inflow (2 cfs) is the boundary condition at the upstream end of Buckmire Slough to keep water flowing though the reach. This is a small inflow, which is easily cleared out of Buckmire Slough if the tailwater – Lake River – is low enough.

The culvert invert elevations through each barrier have been estimated from field visits and pictures, but survey data of these structures is not available. Generally speaking, this is not a hindrance to finding the correct water surface elevations over the modeled time period as the high tail water in Lake River limits flow from Buckmire Slough much more than the culverts’ invert elevation. Furthermore, these culverts will be removed, along with the earthen barriers around them, for the proposed project.


Figure 10: Buckmire Slough in LCR RAS model

Figure 11: Buckmire Slough in modified model

Vancouver Lake

Shillapoo Lake

Vancouver Lake

Sauvie Island Sauvie Island

Shillapoo Lake

2‐D Flow Areas

Buckmire Slough


4.1.2 Additional 2-D Elements Bathymetry has also been added to Caterpillar Slough and the wetland area adjacent to the high ground between the project area and Shillapoo Lake. EC-HY made these areas 2-D flow areas, along with the Pencil Lake area and the agricultural area bounded by Buckmire Slough, Highway 501 and the flushing channel to the south. Some additional modifications to the terrain were made to increase connectivity between the 2-D flow areas. Each culvert that connects to a 2-D flow area must be above the ground that it connects to. Usually these culverts daylight some distance into the 2-D, meaning that the ground is not low enough to connect to these culverts on the edge. Small channels have been burned into the terrain to allow for the connectivity of the culverts. The four 2-D areas serve four different functions within the model. Caterpillar (Caterpillar Slough) follows the stage of the Columbia River, with somewhat lower velocities, and supplies water to the interior of the leveed area in the event of overtopping. HartMcBride (Hart and McBride Lakes Complex) moves water from the overtopped levee to Buckmire Slough. WestRook (Pencil Lake and Rookery Complex) distributes overflow from HartMcBride to the adjacent lands to the south. Conn2 (Ag Parcel 5) serves as an overflow from Buckmire Slough and attenuates the rising and falling limbs of the hydrograph of the Slough if it is flooded. Figure 13 shows the layout of the 2-D areas with the Columbia River on the left and Buckmire Slough to the right. Figure 12 shows a detail of the 2-D mesh and the DEM underlying it; see the inset of Figure 13 for the location of the detail within the whole site.

Figure 12: Detail of 2‐D flow area mesh with underlying terrain


Figure 13: 2‐D flow areas and their positions within the RAS model

4.2 Assumptions To be completed at end of study.

Vancouver Lake

Shillapoo Lake

Columbia River

Buckmire Slough

Detail Area (Figure 12)


4.3 Conditions Modeled This study models three different high water conditions for 30 days each. As noted above, they are February 1996 (Jan 30 to Mar 1), June 1999 (May 24 to Jun 23) and January 2009 (Dec 24 to Jan 23). Stage and flow hydrographs for Vancouver, WA and St. Helens, OR are presented in Figure 14 and Figure 15, respectively.

Figure 14: Modeled Flow and Stage at Vancouver for modeled time periods

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Figure 15: Modeled Flow and Stage at St. Helens for modeled time periods

The stage and flow of February 1996 is uniquely large since the Columbia and Willamette flood control reservoirs were constructed to the extent that they are today. It is a winter storm (rain falling on snow); it has a fast rise and fall and is the only event known to overtop the levees in the project area since at least 1973. Like February 1996, January 2009 is a winter event with relatively fast rise and fall. It peaks a couple of feet higher than June 1999, but has a smaller overall volume. This is typical in the LCR: the freshet brings prolonged high stages and flows but does not reach the highest stages of winter storms. Comparing the St. Helens and Vancouver charts brings out the main difference between winter and freshet flows. Winter highs are locally driven events, whereas the freshet is driven by snow melt in the upper Columbia River basin and local contributions are small. The two largest flow contributions between Vancouver and St. Helens are the Willamette and Lewis Rivers. They nearly double the flow between these two points during 1996 and 2009, but only add about 15% to the total in 1999. It is important to note that June 1999 and January 2009 were selected because they are not exceptional events. They are selected because they reach approximately 50% ACE stage for freshet and winter events. In other words, about half of all years will see a period above these presented.

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4.4 Results The study identifies changes in water surface elevation and velocity into areas in and around the proposed project using indicator hydrograph and raster datasets. Various profiles of on-site and off-site locations area presented below. A smaller version of Figure 2 is presented here for reference in Figure 16, along with the locations for various results figures presented below.

Figure 16: Site overview with profile (pink) and hydrograph (yellow) locations

Figure 17 and Figure 18 show the maximum Columbia River and Lake River water surface elevations, respectively, for each of the three modeled time periods. The vertical lines across the profiles represent locations of interest along the profile. The contrast between 1996 and the two others (that do not overtop the Caterpillar Slough levee), is telling for this project. The profile elevations for the Columbia River and Lake River are similar for 1996, whereas Lake River is much lower during 1999 and 2009 (compare the elevations around Caterpillar Slough and Buckmire Slough). Reconnecting the Columbia River to Lake River through Buckmire Slough will remove some or all of this difference in water surface elevation.


Figure 17: Modeled Columbia River profile, St. Helens, OR to the Willamette River

Figure 18: Modeled Lake River profile from the Columbia River to Vancouver Lake

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Figure 19: Modeled Stage at Caterpillar Slough and flow into Hart and McBride Lakes complex

Figure 19 shows the flow from Caterpillar Slough into the Hart and McBride Lakes complex. The stage represented here is within Caterpillar Slough itself; this is nearly identical to the stage in the Columbia River. As previously stated, only the 1996 flood crests higher than the levee; 1999 and 2009 show zero flow. Figure 20 picks up on the other side of the levee to the east. The stage within Hart and McBride Lakes complex is charted along with the total flow to the Pencil Lake and Rookery complex. There are four phases of interest during the 1996 event: initial positive flow originating from the Caterpillar Slough overflow, reverse flow originating from a longer, slightly higher low point along the north side of the flushing channel, zero flow during equalized water surface elevations within the project site and finally reverse flow as the entire site drains through Hart-McBride into Buckmire Slough. The slow rise seen in the 1999 and 2009 stages is due to the 2 cfs flow into Buckmire Slough. The stage downstream of the highway 501 culvert is generally higher than the stage within the Slough due to tide gate, so this flow backwaters into Hart-McBride. As the stage in Lake River, and the downstream end of Buckmire Slough, falls, this interior accumulation will clear as well, as seen in the end of the 2009 stage as compared to the 1999 stage.

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Figure 20: Stage in Hart and McBride Lake complex and net flow to Pencil Lake and Rookery Complex

Figure 21: Flow and Stage upstream of most downstream earthen barrier (removed in Otak plans) in Buckmire Slough

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Figure 21 shows stage and flow within Buckmire Slough restricted from Lake River by the most downstream barrier. This barrier and culvert is slated to be removed with the Otak Phase 1 construction plans. Most of the flow is negative in this case. In other words, the flow is backing up into the Slough from Lake River through the collapsed culvert and over the embankment (when Lake River stages are high enough – the low elevation is 19.1 ft). The peak stages are delayed significantly from the Columbia River and somewhat from Lake River.

Figure 22: Stage and inflow of Shillapoo Lake

Shillapoo Lake results are shown in Figure 22. Only February 1996 has any inflow into the site and the model does not include the known levee breach at the current location of the pump station to Lake River. However, the lowest point of the levee system connects to Shillapoo Lake from Buckmire Slough approximately at the location of Figure 21; it starts to overtop about two hours before the levee at Caterpillar Slough. Shillapoo Lake is dry during the 1999 and 2009 simulations. Vancouver Lake is much more connected due to the flushing channel and Lake River, as shown by Figure 23. The flow is more cyclical as the flood wave moves from the Columbia River through the flushing channel and from the Columbia River back up Lake River. Stage mimics the Columbia River slightly delayed, even if the inflow is erratic.

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Figure 23: Stage and net inflow of Vancouver Lake

Depth grids throughout the site are provided with this study to show how the proposed project will affect surface water flow and elevation. The maximum depth grids for each of the modeled periods are shown in Figure 24, Figure 25 and Figure 26 for February 1996, June 1999 and January 2009, respectively. The earthen barriers along Buckmire Slough significantly alter the maximum depths reaches in 1999 and 2009, as shown in Figure 21. The inundation within the Hart and McBride Lakes complex is very limited due to the tide gate on the east side of the highway 501 culvert (barrier 4 in Figure 1). The site is fully inundated during February 1996 and does not return to dry during the 30-day model run due to insufficient drainage capacity. It is evident in the aerial photography that most of the lakes within the project site, and most of Vancouver Lake, do not show as inundated in Figure 25 and Figure 26. In the case of the project site, bathymetry was not collected for most of these lakes, with the exception being the channel shown as inundated. The water surface in the LiDAR is above the highest elevation reached during these model runs. The portion of Vancouver Lake not shown as inundated is due the extents of the DEM; the majority of the lake is not included, the exception of the connection to Lake River and edge along Buckmire Slough, which are shown as inundated in the figures below. These mapping inconsistencies do not affect the hydraulics within the model.

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Figure 24: Maximum depth for February 1996 Figure 25: Maximum depth for June 1999


Figure 26: Maximum depth for January 2009


Figure 27: 2 hours after start of levee overtop during February 1996

The triangles in Figure 27 show one additional inconsistency in the depth grids during certain time steps and only within the 2-D flow areas. This detail is in the northern part of the Hart and McBride Lakes complex, in nearly the same location shown in the 2-D flow area detail shown in Figure 12. These triangles represent overland flow as it moves from one cell to the next. Each cell in the 2-D area has a single water surface elevation that does not necessarily reach the highest DEM elevation that forms the bottom of the cell. The lower part of each cell is filled first and the high side never fills as each cell empties into the lower adjacent cell – creating these triangles – until ponding occurs in a bowl lower on the slope. In this case, the low side of each cell in the circled area above is the right side, indicating flow from the levee into the project site. Hourly depth grids are provided for each of the three model runs. At a resolution of 1 meter, the same as the study DEM, this totals about 41 GB of data for the existing conditions results.

Overland Flow

Ponding


5.0 ALTERNATIVE 1 CONDITIONS MODELING Alternative 1 proposes several modifications to the current site, connecting Hart-McBride, Pencil Lake-Rookery, Ag Parcel 5 and Buckmire Slough to the direct influence of the Columbia River. This is mainly accomplished by breaching the levee separating Hart-McBride from Caterpillar Slough and removing the earthen embankments along Buckmire Slough. Off-site lands are protected by proposed levee improvements. Several hydraulic structures are also removed in this alternative. Alternative 1 proposes two breaches of the levee system adjacent to Caterpillar Slough. The northern breach and its associated channel connect the Slough to Mathews Lake. The northern breach is trapezoidal with a bottom with of 40 ft, a thalweg elevation of 8.5 feet NAVD88 and 2:1 side slopes. A second breach is proposed to the south along with associated channel network. The southern beach has a bottom with of 20 ft, a thalweg elevation of 11.0 ft and 2:1 side slopes. In addition to the above terrain modifications, LCEP has also added new survey data to the study terrain within Matthews Lake and selected other locations, though these survey modifications are


not shown in the difference plot in


Figure 28. The Existing Conditions model has not been updated with this information as they are not expected to alter Existing Condition results for flood conditions – see Assumptions (below). 5.1 Description of Models In order to accurately model Alternative 1, the Corps made several changes to the existing model geometry. All changes in this section are done with the Existing Conditions model as a starting point. Therefore, all of the information given in previous sections apply to this model and should be reviewed carefully before applying the results of this model. Given the rapid development of HEC-RAS beta software, several additions made available since Existing Conditions have been useful to the development of the Alternative 1 geometry. In particular, the break line capability within the 2-D mesh has improved greatly since the construction of the existing conditions model; this has been used extensively to modify the 2-D mesh.

5.1.1 1-D Elements Modifications The 1-D elements have changed in two primary ways: in service of the terrain modifications within the 2-D areas and to reflect the proposed changes within Buckmire Slough. Three of the 2-D areas (Caterpillar, HartMcBride and WestRook) are connected with weirs (storage area connections in RAS). Alternative 1 proposed channels flow through these weirs and therefore these weirs were modified to conform to the new terrain. Figures 29 and 30 illustrate the modifications made to the 1-D elements connecting Caterpillar and HartMcBride. Note the deep notch in Figure 30 representing the north breach. In order to more effectively analyze results, this weir was split into two pieces – one for each breach – in Alternative 1, hence the change in weir length. A similar chart is available for the south breach but is not presented here.


Figure 28: Alternative 1 Model Modifications


Figure 29: Weir connection from Caterpillar to HartMcBride in effective conditions.

Figure 30: North breach connection from Caterpillar to HartMcBride in Alternative 1.


Additionally, Alternative 1 raises embankments around the outside of the proposed project site (e.g. Lower River Rd) to maintain the current level of protection for the adjacent lands. The current minimum levee height is 27.5 ft. In some cases the proposed high ground is not at the same location as the current high ground. In these cases, the connections to the adjacent storage areas are assigned the 27.5-ft elevation even if the embankment is not directly under the edge of the 2-D area. This is done to minimize the number of modifications needed between iterations for this study. The 1-D structure controls the connection between the various areas (in the form of a station-elevation chart) so the hydraulics remain the same regardless of modeling approach. Alternative 1 changes Buckmire Slough in significant ways. The Otak plans show the removal barriers 1 and 2 (see Figure 1) and a replacement with a pedestrian bridge at barrier 2. Alternative 1 also removes barriers 3 and 4, a service road and highway stub respectively. In the hydraulic model, none of these locations are replaced with any structures save the pedestrian bridge mentioned above. Previously, these barriers within the model had enhanced stability within the model by keeping Buckmire Slough, along with the Slough’s low connection to the 2-D area HartMcBride, flooded with a least a few feet of water. Removing these blocks means that water flows more freely and the stability of the model decreases. In order to maintain stability and functionality across the variety of flows necessary for the 180-day run, the engineer added two small weirs within Buckmire Slough. One is directly downstream of the pedestrian bridge and the other at the confluence with Lake River. In addition, base flow at the upstream end of Buckmire Slough is increased to 8 cfs (from 2 cfs) and the upstream end of the slough has been flattened. Figure 31 and Figure 32 show the qualitative difference between these the two different profiles. Note the flattened right (upstream) side and the reduction in the number of structures.

Figure 31: Buckmire Slough profile for Alternative 1 with adjustments for model stability (Lake River connection on the left).


Figure 32: Buckmire Slough profile for the Existing Conditions (Lake River connection on the left).

5.1.2 2-D Elements Modifications The Corps made several modifications to the three 2-D elements to the west of Buckmire Slough (Ag Parcel 5 is unchanged due to the lack of modifications). The two proposed levee breaches flow from Caterpillar Slough and connect the various low areas within the HartMcBride and WestRook 2-D areas. The north breach is at elevation 8.5 ft and the south breach – about a half mile upstream along Caterpillar Slough – is at 11.0 ft. This difference in elevation reflects the prevailing ground elevation of the areas that each breach and channel system connects to directly. The 2-D mesh has been modified to get accurate velocity within the channels. The mesh spacing is narrower (10-30 feet) in the areas around the constructed channels, with the original mesh spacing (at 40-50 feet) maintained in most other locations. The May 2015 beta version of HEC-RAS 5.0 supports the use of break lines and densification of the mesh around these break lines. The cell spacing for the channels has been set to 10 feet in most cases (channel fit determined the exact spacing for each channel), with added intermediate cells between the prevailing and channel spacing. These are necessary to avoid an abrupt transition between cell sizes and stay under the 8-sided-cell limit in RAS. Figure 33 shows an example of the 2-D mesh modifications at the north breach. This is the detail location shown in Figure 12 in the Existing Conditions; many similar modifications have been made throughout the


2-D areas in line with the terrain modifications in

Figure 28.


Figure 33: North breach with channel cut and 2‐D mesh modifications.

5.2 Assumptions Comparison between the Existing Condition and Alternative 1 Condition terrains show that some terrain features other than Alternative 1 construction activities have been modified. Added bathymetric data in interior lakes is an example newly incorporated data not available when the Corps ran the Existing Conditions model. These differences only have an effect on low flow, with very limited effect on the water surface elevations during the 1996 event. The 1999 and 2009 events do not overtop the levees during the existing conditions run, so comparisons with the previous terrain are unaffected. It is assumed that these minor changes do not affect results and do not prevent comparison to existing conditions. Due to the greater connectivity between the 1-D and 2-D elements of the Alternative 1 geometry, a shorter computation time step is necessary to maintain model stability. It is assumed that

2‐D RAS

Break lines

Denser 2‐D

Cell Spacing


Existing Condition and Alternative Conditions hydraulic outputs are still comparable regardless of changes in computation time step required for stability. It is assumed that a model without water loss due to evaporation and infiltration or gain due to seepage is acceptable for all the analysis to be performed with modeling results. This can mean that some areas in the model will hold water permanently when the actual site would dry out instead. 5.3 Results of Long Term Run The focus of the analysis of Alternative 1 has been a 180-day run, representative of lower flow and mid-level freshet. The time window selected by the team was February 1, 2009 to July 31, 2009. The Corps has implemented the same lower Columbia River hydrology as was presented in section 3.1. Modeled stage and flow at the Vancouver, WA gage location are shown in Figure 34. The shape of the stage is echoed throughout the Alternative 1 results. The main differences for each chart will be whether there is a minimum elevation (an area that dries out when Columbia River is lower) and how much tidal damping and elevation loss occurs (based on hydraulic losses in connections to the Columbia).


Figure 34: Flow and stage at Vancouver, WA for 180‐day run.

5.3.1 Water Levels and Site Elevation Gradients In general, the hydraulic grade line (HGL) falls as water moves from the Columbia River across the site to Buckmire Slough and Lake River. In Existing Conditions the profile of Lake River is fairly flat from its confluence with the Columbia River about 12 miles downstream of Vancouver Lake. Vancouver Lake stages are reliably lower that adjacent Columbia River stages in all but extreme low flow and tide conditions. Figure 35 shows locations where stage hydrographs have been extracted for analysis and comparison. The main conveyance through the site travels from the North Breach to Mathews North and Mathews South and on to Lake River Connection via the Buckmire Connection and Highway. The highest point in the system – the point at which water does not return to the Columbia River during regular stages and tides – is the undisturbed ground just south of Mathews North. Once water makes it out of the channel from the North Breach and over this point at elevation 10.1 ft NAVD88, it will eventually flow through to Lake River. Mathews Lake generally slopes downhill from the north, so the point at which constructed channel stops will determine this point of no return.

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Figure 35: Surface water elevation and water balance locations.


Figure 36: Comparison of Mathews North to the North Breach

Stages at Mathews North, which is within the constructed channel, spend the majority of their time below stages at the North Breach, as shown above in Figure 36. The times that it is above mostly have to do with the delay in the tidal cycle during periods of low water. Water is filling and emptying the constructed channel itself, not emptying the site as a whole. Moving downstream to the Buckmire Connection location – where the project proposes the removal of a culvert and stop log structure – water surface elevations have fallen to where they sit about 0.1 to 0.2 feet below the breach. The relatively brief periods where the connection is above the breach are, like Mathews North, an effect of tidal cycle delay. When the tidal amplitude is compressed during the freshet (around days 110 to 130) and Columbia stages are high, this cyclical nature disappears and the connection stays at about 0.5 feet below the breach, reflecting higher flow and energy loss through the site. The Lake River Connection location, in Figure 38, looks similar to the Buckmire Connection. Once again, the water surface elevation has dropped and the tidal cycle has damped further. At this point, Lake River is rarely above the North Breach, with the average difference at about -0.45 feet. During the peak of the 2009 freshet, the Lake River Connection stages are about 0.9 feet below stages at the North Breach.

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Figure 37: The Buckmire Connection as compared to the North Breach and Mathews South.

Figure 38: Lake River connection as compared to the North Breach and Buckmire Connection.

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The South Breach behaves differently from the North Breach because it, and the ground that it leads to, is higher. It also tends to hold water after it is flooded as shown after day 150 in Figure 39. There is no water loss (i.e. evaporation or infiltration) in this model, so the maintenance of this ponded water is suspect after the summer freshet. The minimum elevation of the breach is 11.0 feet, so the area is dry when the chart is at this elevation. Both the right and left portions of this chart reflect that Pencil is more or less disconnected during low water and only is active with the run up to and during the freshet. It behaves similar to the Mathews/North Breach relationship outlined above: mostly below the breach, with a delay in the tidal cycle. The East and West Rookery track Pencil very closely; as they mostly show redundant information, they are not presented here.

Figure 39: Pencil split as compared to the South Breach.

Located between Pencil and Mathews, Bass Hart shows how the two breaches interact and how water flows through the site. Figure 40 shows that Bass Hart is above the North Breach when it is dry (the minimum elevation is above the north constructed channel at 9.1 feet). The tidal flow signal delay is significant, so it feeds Buckmire Slough for some time after the Columbia is below 10.0 feet. Effectively, this area works as a partially connected holding pond, damping the tidal signal for the site and moving water toward Mathews. Water travels from the South Breach through Pencil and Bass Hart toward Mathews and Buckmire Slough during periods of high water. Water does not return to Columbia River under the Alternative 1 conditions once it reaches this location.

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Figure 40: Bass Hart and comparison to the breaches.

Other water surface elevation charts not presented here are available in the document WSEL charts.xlsx. These include the North and South Breach, North and South McBride, East and West Rookery, Twin Ponds and Highway 501. The charts shown and described in this section express the major trends observed within the project domain. 5.3.2 Site Water Balance Alternative 1 modeling shows that water flux in the restoration site varies significantly based on stage in the Columbia. Figure 41 shows flows at various locations within the restoration area for early February 2009. During this period, flows in the Columbia are less than 150 kcfs with tidal stages at the Vancouver gage slightly above MHHW and MLLW at tidal peaks and troughs respectively. Positive flow is toward Lake River in all charts in this section. During this period there is a net positive flux from the Columbia to Lake River as seen the North Breach flow hydrograph. The North Breach is only active at the peak of the high tide with more water moving positively into the site than negatively returning to the Columbia. The South Breach does not activate during this period. The majority of the water moving into and out of the site comes from Lake River. Significant negative flows (water moving from Lake River toward the Columbia) are still seen as far upstream as the Highway Cut location. The Buckmire Connection location has a signal with both a positive flow during the rising limb of the Columbia tidal signal and negative flow on the falling limb, much like North Breach. This indicates that flow upstream of the Buckmire Connection is

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dominated by the Columbia, while flow downstream of the Highway Cut is dominated by Lake River during these low Columbia flow periods. Hydraulics internal to the phase 2 restoration area during periods of low flow in the Columbia show that north/south exchange is limited during normal flow and tidal conditions; the net flow between HartMcBride and WestRook is nearly zero for the entire 14 days.

Figure 41: Tidal water exchange for normal tides. At Vancouver Gage: MHHW = 10.05 ft NAVD88, MLLW = 6.71 ft NAVD88. Note that Highway Cut, Pedestrian Bridge and Lake River Connection are influenced by a positive 8 cfs base flow in Buckmire

Slough required for model stability.

Moving to a higher flow time period (Figure 42, Columbia flows greater than 250 kcfs), the freshet moves much more water through the site. The primary water supply is the North Breach, with the South Breach supplying less than 25% of the water during high water. Note that West Rookery begins to fill even before the South Breach is drawing significant water to the site. The extreme looking nature of flow into Caterpillar from the Columbia reflects the volume exchange between the Columbia River and Caterpillar Slough as stages in both rises. Most of this volume is the Slough itself filling and draining and has little to do with the Alternative 1 conditions. During the high water period of the freshet, water surface elevations are fairly constant with all flow traveling through the phase 2 project to Buckmire Slough and eventually to Lake River. The site empties when the outflow onto Lake River is greater than the inflow through the north and south breaches, about day 24 in Figure 42, when Caterpillar Slough also empties back to the Columbia River.

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Figure 42: Water Balance for the freshet.

Figure 43: Weekly net flow for 180‐day simulation.

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The weekly net flow across the site is quite variable depending on the Columbia River stage. As the Columbia rises, more water is pushed through the site to Buckmire Slough and Lake River; the freshet is responsible for most of the volume reflected in Figure 43. As with the previous chart, the Caterpillar Slough graph reflects the volume of the Slough itself. As previously mentioned, the Corps added an 8 cfs flow to the upstream end of Buckmire Slough for model stability. 8 cfs equals about 0.7 ac-ft per hour, 16 ac-ft per day and 111 ac-ft per week. Tracking this extra water is not possible within the model due to the complex nature of the tidal influences and many points of connection. However, as shown by the scale of the above charts, this volume is insignificant compared to the total volume moving through the site. The flow becomes apparent at the daily scale for low flow events and should be considered when contemplating the meaning of Figure 41. EC-HY has made no effort to subtract this base flow volume out of the model. 5.3.3 Velocity Velocities across the site are low. The maximum velocity through the breaches between Caterpillar Slough and HartMcBride is about 2.5-3.0 feet per second (fps) during the 180-day run. The peak velocities for a given event occur during the steepest part of the hydrograph (this is typically, but not necessarily, the rising limb). This holds true for the stage rise during the freshet of the 180-day run, where the maximum velocities occur for this run, as well as the maximum velocity for the February 1996 event. The maximum velocity through the breaches is 4.5-5.0 fps during February 1996 and less for 1999 and 2009. In general, the steepness of the hydrograph – above an elevation that activates sufficient on-site storage, about 13 feet – correlates with high velocities through the levee breaches. Although the steepest hydrographs are the tides, they do not move enough water to the site (there is not sufficient storage a low enough elevation) to force high velocities. The rising limb (Feb 7th to Feb 8th) of the 1996 event is the steepest rise of sufficient elevation that has been modeled for Alternative 1 thus far. Unfortunately, due to the use of beta software for this project, the Corps cannot provide velocity rasters or charts for the 2-D elements at this time. Figure 44 shows velocities in Buckmire Slough (the major 1-D addition to the LCR model for this project), peaking below 1.0 fps during the 180-day run. Negative velocity (away from Lake River) tends to be short, in line with the results presented above in the Water Balance Section.


Figure 44: Velocity in Buckmire Slough for the 180‐day run.

5.4 Alternative 1 Deliverables

The following items are included with this report to assist in the formulation of future alternatives and ecological function modeling.

Excel spreadsheets of model output o WSEL charts.xlsx – water surface elevation at various points o WaterBalance.xlsx – flow across the site with various analysis o Velocities.xlsx – velocity information at various points

Videos of 2-D Results o Freshet.mov – depth of entire site for the freshet high water period o Tides_mid.mov – mid-level view of about a week of tidal cycles o Tides_close.mov – close view of tidal cycles with 2-D grid o WSEL_runup.mov – water surface elevation for entire site during rise to freshet

Depth Rasters of Site o Jan 2009 Max Depth o 180-day run Max Depth o 180-day run Min Depth

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o 180-day run Min Depth after freshet has passed

HDF files of LCR RAS model output from the six 30-day runs that make up the 180-day run

6.0 COMPARISON OF BEFORE AND AFTER PROJECT The Columbia River and Lake River profiles have been affected slightly by the levee breach and redistribution of water. Figure 45 shows the Columbia River Profile in the vicinity of the project site, similar to Figure 17. The dashed lines represent the difference in water surface elevation from the existing conditions. Only the 1996 event raises water surface elevations, and only by 0.01 feet. This is because the site is inundated before the peak arrives under breached conditions; previously, the site filled during high water when the levee overtopped. However the extents of this small water surface rise is quite large: from River Mile 65 (Longview, WA) to River Mile 140 (about 5 miles downstream of Bonneville Dam) on the Columbia River and all the way up the Willamette River to Willamette Falls in Oregon City.

Figure 45: Columbia River profile in vicinity of site and difference to existing conditions

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Alternative 1 also affects the profile of Lake River, although more during the lower events in contrast to the Columbia River profile. Figure 46 shows the profile of Lake River and compares existing conditions to Alternative 1. As expected, the project increases the connectivity to Lake River, dampening its tidal signal and increasing flow in the river. The total changes in water surface elevation are less than 0.06 feet. Alternative 1 raises the water surface of Vancouver Lake, which is reflected in the most upstream extent of Lake River.

Figure 46: Lake River profile and comparison to existing conditions.

As one would expect the site is much more inundated during the January 2009 event with the levees breached. Figure 47 shows much of the site is inundated, a sharp contrast to Figure 26 from Existing Conditions, in which only Mathews Lake was partially inundated.

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Figure 47: Maximum depth grid for Alternative 1 during the January 2009 high water event. This event approximates a 2

year reoccurrence interval event on the Columbia River at this location.


6.1 Points of Comparison To be completed with the selected alternative flood modeling. 6.2 Comparison of Depth Grids To be completed with the selected alternative flood modeling. 7.0 CONCLUSIONS & RECOMMENDATIONS To be completed with the selected alternative flood modeling. 7.1 Identified Risk Factors To be completed with the selected alternative flood modeling.

7.1.1 Flood Risk To be completed with the selected alternative flood modeling. 7.1.2 Agricultural/Infrastructure Risk To be completed with the selected alternative flood modeling.

7.2 Other Considerations To be completed with the selected alternative flood modeling.


8.0 REFERENCES

USACE Hydrologic Engineering Center. 2011. Draft - Unsteady Flow Hydraulic Model of the Lower Columbia River System from Bonneville Dam to the Pacific Ocean, Columbia River Treaty Review Studies

Buckmire Slough Restoration Project: Design Basis, Otak, February 27, 2014

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A-1

APPENDIX A

To be completed at end of study.

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