swampcreek_ap_b3

8/7/2019 SwampCreek_Ap_B3

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Snohomish County

Swamp Creek Drainage Needs Report

APPENDIX B3

Hydraulic Model

Development and

Application for

North Swamp Creek

Subbasin


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Appendix B3. Hydraulic Model Development andApplication for the North Swamp Creek Subbasin

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Contents

B3.1 Introduction....................................................................................................... B3-1B3.2Data Collection and Field Observation.............................................................. B3-1

B3.2.1Drainage System Survey.................................................................... B3-2B3.2.2Basin Reconnaissance.......................................................................B3-2

B3.3HEC-RAS Development and Results ................................................................B3-9B3.3.1Existing Condition Model ....................................................................B3-9B3.3.2 Model Results and Problem Identification with Existing

Conditions Flows ..............................................................................B3-24B3.3.3Model Results and Problem Identification with Future

Conditions Flows ..............................................................................B3-27B3.4CIP Alternatives .............................................................................................. B3-27

B3.4.1CIP Alternative 1................................................................................ B3-28B3.4.2CIP Alternative 2................................................................................ B3-31

B3.5 References ..................................................................................................... B3-36AttachmentsAttachment B3-1 Additional Problem Areas Identified But Not Studied (Swamp Creek

North Subbasin)

Figures

B3-1. North Swamp Creek Hydraulic Model Schematic forHEC-RAS Model Lake Stickney ................................................................B3-11

B3-2. North Swamp Creek Hydraulic Model Schematic forHEC-RAS Model West Tributary ...............................................................B3-12

B3-3. North Swamp Creek Hydraulic Model Schematic forHEC-RAS Model North Tributary...............................................................B3-13

Tables

B3-1. North Swamp Creek Subbasin Drainage Complaints(1996 through 2000) ......................................................................................B3-3

B3-2. Model Cross Sections..................................................................................B3-16B3-3. Physical Extents of FTABLEs Generated from HEC-RAS............................B3-22B3-4. HEC-RAS Flow Model Input for Existing and Future Land Use

Conditions....................................................................................................B3-23

B3-5. HEC-RAS Hydraulic Model Results Summary for Existing System withExisting and Future Land Use for North Swamp Creek Subbasin.................B3-25

B3-6. Proposed Culvert and Bridge Improvements forCIP Modeling Alternatives 1 and 2 for North Swamp Creek Subbasin..........B3-29

B3-7. HEC-RAS Hydraulic Model Results Summary for Existing System withExisting and Future Land Use Conditions, and for CIP ModelingAlternatives 1 and 2 for North Swamp Creek Subbasin................................ B3-33


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Appendix B3. Hydraulic Model Developmentand Application for the North Swamp CreekSubbasin

B3.1 Introduction

One hydraulic model was selected and used for the stream reaches and drainagesystems for which detailed hydraulic analyses were conducted in the North SwampCreek Subbasin. The model was selected based on the primary type of drainagesystem that was being analyzed. The model was also used to develop additional flowrouting tables for the HSPF hydrologic model.

Three separate HEC-RAS models were developed for detailed hydraulic analysis ofthree drainage systems in the North Swamp Creek Subbasin. The North Tributarymodel extends from the upstream end of a culvert crossing 112th Street at the north orupstream end, to downstream of a culvert crossing Center Road near the intersection ofCenter Road and Admiralty Way. The West Tributary model extends from downstreamof Center Road near the intersection of Center Road and Beverly Park Road at theupstream end, to 128th Place SW near its intersection with Alexander Road at thedownstream end. The modeled reach of Swamp Creek extends from the outfall of LakeStickney at the north or upstream end, to Manor Way at the downstream end. The HEC-RAS model was selected because it is well-suited to evaluate the hydraulic capacity ofopen channel systems where backwater conditions (i.e., high upstream water levelscaused by downstream flow restrictions exist.

B3.2 Data Collection and Field Observation

Data collection included basin reconnaissance and field survey as well as a meeting withCounty staff to review historic flooding problems. Previous studies were also reviewed.

In addition, historic drainage complaints occurring within the last six years werecompiled. Table B3-1 summarizes the drainage complaints for North Swamp Creek.Since budget constraints did not allow for all of the drainage systems in the study area tobe analyzed, including some with historical flooding problems, County staff needed toselect the systems in which detailed hydraulic analyses would be conducted. In general,those systems with more frequent flooding problems, or with a greater impact to thepublic, were selected for the detailed hydraulic analyses. Attachment B3-1 contains a

list of additional drainage systems that will need to be analyzed in the future.An initial field reconnaissance was conducted to field locate the stream and to observethe stream conditions and surrounding areas. The initial field reconnaissance wasfollowed by a field survey to obtain geometric data for the hydraulic analysis. Culvertand stream channel data were collected and used to analyze the system capacity of theidentified drainage systems in the North Swamp Creek Subbasin. Figure 3-1c shows thelocations where the stream channels and road culverts were surveyed to provide inputdata for use in the HEC-RAS models.


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The survey data included road culverts and stream channel cross sections. Roadculvert data consisted of culvert upstream and downstream inverts, culvert length,culvert size and shape, culvert material, and top of road (for use in road overtoppinganalysis). Stream channel cross section data defined the geometry of the natural streamchannels immediately upstream and downstream of the road culverts. The field surveydata were input into the County's Geographic Information System (GIS)

B3.2.1 Drainage System Survey

Global Positioning System (GPS) equipment was used to conduct surveys of existingsurface water facilities within the basins. This process allows rapid and accurate datacollection and the ability for the data to be downloaded into computers and viewed withina GIS environment. GPS data were reviewed to find any potential problems that mightrequire verification.

The surveys were conducted using high accuracy, survey-grade GPS equipment, with ahorizontal accuracy of 2 centimeters and a vertical accuracy of 4 centimeters relativeto control. In addition, all drainage facilities were directly measured.

GIS coverages were created from the survey data that were downloaded from the GPSequipment. Data processing program routines were developed by the County to assistin the construction of the drainage network from the point features collected by the GPSunits. Cross section and drainage feature information that was collected from the surveywas then extracted from the GIS coverage and used in the hydraulic analyses. Table 3-2 and Figure 3-1a show the existing drainage facilities that were inventoried as well asthe drainage network that connects these facilities.

B3.2.2 Basin Reconnaissance

Basin reconnaissance conducted by project staff included review of surveyed data andother basin information. Project staff visited the North Swamp Creek Subbasin onseveral occasions during summer and fall 2001. Qualitative observations made during

these visits supplement the survey data collected by the survey crews.

The information collected and the activities performed during the field visits included:

Observing the drainage system being modeled to assist in coordinating the surveyand data collection effort.

Assessing the condition of hydraulic structures and stream reaches for model inputparameter development.

Identifying and observing suspected problem areas.


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Table B3-1North Swamp Creek Subbasin Drainage Complaints (1996 through 2000)

SWM No. Address General Problem Problem Resolution

19960016 1044 93rd St SW CITY Resident requests installation ofdrainage ditch along frontage of Privateproperty

Service Request sent to RoadMaintenance for consideration

19960021 3419 133rd St SWBothell 98012-1271

Water from nearby construction flowingacross street and onto Private propertyback yard

Construction manager of project to extendpipe to residents property; no Countyaction required

19960059 9300 Sharon DrEverett 98204

Private property yards/area underhouse showing standing water due toplugged ditches and natural topographyof area

Service request sent to RoadMaintenance to clean ditches; naturaltopography flat; recommended thatresident raise lower portions of yard andslop toward ditch

19960078 2032 106th Pl SWEverett 98204

Private property back yard flooding dueto retaining wall built by neighborbehind

Private system; no County actionrequired; alternative drain systemsrecommended

19960089 1511 Hollowdale PlEverett 98204

Private property yard/driveway flooding Service Request sent to RoadMaintenance

19960162 10507 Rosewood AveEverett 98204

Private property crawl space flooding(probably) due to high levels of groundwater

Natural event; no County action required;additional drainage recommended

19960222 10329 16th Pl WEverett 98204

Water flowing from Private propertyyard over sidewalk due to natural slope

No County action required; recommendedto construct weep holes in sidewalk toforce water into gutter line

19960243 12904 29th Ave WLynnwood 98037

Private property yard flooding asreceives runoff from poorly crownedPrivately-owned road

PDS to help contact permit holder of road,who is responsible to maintain; no Countyaction required

19960282 1426 100th St SWEverett 98204

Resident wishes to channel stream(natural drainage course) flowingacross Private property back yard

Advised to draw plan and submit to PDSfor permitting; no County action required

19960284 10106 Montana RdEverett 98204

Resident claims increased water flow toyard due to nearby development; alsowants County to re-route drainage off ofPrivate property in order to subdivide

No County action required; see PDS re:increased water from development;County cannot re-route natural drainagefor possible Private profit

19960325 607 91st Pl SWEverett

Resident wants to know if responsiblefor cleaning catch basin in 10easement on Private property; also, canhe build next to it?

Resident responsible; County can servicein emergency as pipe is accessible fromstreet; may build no closer than 10 nearwithout variance from PDS

19960351 12007 Beverly Park RdEverett 98204

Resident requests drainage ditch onPrivate property be cleaned and dugdeeper

Private system; no County actionrequired; refer to PDS for permitting todeepen ditch

19960387 10130 19th Pl W CITY Request to alter easement on Privateproperty

Request approved, with condition thatowner remove/replace fence/shrubberyshould County need to access easement

19960419 1431 108th St SWEverett 98204

Private property driveway/garageflooding due to plugged driveway drainand ineffective berm

Placed on Small Project list for 1997

19960448 10430 Holly Dr Everett98205

Private property driveway/garageflooding as road runoff not entirelyreaching catch basin

Service request sent to RoadMaintenance to install berm alongfrontage to better direct water to CB; CBlowered, pipe cleared


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Table B3-1 (continued)North Swamp Creek Subbasin Drainage Complaints (1996 through 2000)


19960512 Sno Co R/M Cross culvert near 10626 Holly Dr

Everett 98204 too small

Placed on Potential Project list to upsize

cross culvert under Holly Drive

19960535 11025 6th Ave WEverett 98204

Private property flooding due to pluggedditches, recent development, andnatural topography

Service Request sent to RoadMaintenance to clean pipes/ditches;recommended additional yard drainage

19960593 10032 19th Pl WEverett 98204

Private property flooding fromoverflowing pond behind house (relatedto problem 19960595)

None stated

19960595 10104 19th Pl WEverett 98204

Private property flooding due to PostOffice and Boeing development, andchannel constriction by neighboringresident

Complaint Investigation Request sent toPDS re: is constriction in violation; for PO-related concerns, see City of Everett; forBoeing-related, see Mike McCrorie ofPDS

19970207 13715 Manor WayLynnwood 98037

Private property flooding/house damagedue to nearby creek (Swamp) rising andundersized culvert pipes

Placed on Potential Project list forhydraulic analysis of Swamp Creek andpotential upsize of existing pipes


Resident reports Private propertyflooding from Swamp Creek andpotential for more from County walkwaybeing built

No evidence of existing problem; noCounty action required

19970227 2615 Russell WayEverett 98204

Resident reports Private propertyflooding due to inadequately sizeddrainage system

None stated

19970260 7228 210th St SWEdmonds 98026

Private property house flooding fromstreet runoff

Service Request sent to RoadMaintenance to extend drain bar acrossdriveway to drainage ditch, to divert wateraway from property

19970268 1400 N Lake Stickney

Dr Lynnwood

Request for technical advise per

problem 94-588

"Filed Claim for Damages. 8/19/97 Met

with Ray Dickerson, Senior ClaimsAdjuster for Giesy, Greer, & Gunn, Inc. todiscuss Mrs. Schroth's (Zahner) claim."

19970271 1027 112th St SWEverett 98204

Private property flooding due to pluggeddrainage system

Residents to refer to Hampton Courtwho is responsible for Systemmaintenance; no County action required

19970281 P.O. Box 3666Bellevue 98009

Kiley Court Condos unit back yardsshowing standing water from high rainactivity and detention pond backing upinto drainage system

Adjacent wetland area encroaching;recommended to install in-line back-flowpreventer valve and berm; no Countyaction required

19970362 13306 17th Ave WEverett 98204

Private property flooding/damage(possibly) from Lake Serene (Stickney)overflow

No County action required; recommendedto build berm on property

19970381 19401 40th Ave W

Lynnwood 98036

Private property flooding from

overflowing detention pond owned byAirport Road Business Park

Owner should review design for

adequacy; contact nearby propertyowners also impacted to considercooperating to mitigate problem; noCounty action required

19970390 3526 121st St SWEverett 98204

Lower apartment and backyard floodingfrom street overflow

Service Request sent to RoadMaintenance to redirect flow of stormrunoff away from driveway into drainageditch


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19970403 702 91st Pl SWEverett 98204

Easement Alteration Application.

10-foot private drainage easementBuilding garage 1 foot west of 10-footeasement line

None stated


Private property yard flooding due toheavy rains

Natural event; no County action required;recommend alternative drain systems andincorporating natural drainage intolandscape

19970432 10701 Holly Dr Everett98204

Private property back yard flooding asditch overflows and water does notreach catch basin

Holly Drive Culvert Replacement Projectinstalled asphalt berm around CB andimproved ditch

19970442 Road Maintenance /2W

Ditch overflows in heavy rain; cleaningditch and catch basin did not resolveproblem

Placed on Potential Project list to installdrainage system to direct water to thesouth or west

19970466 None stated Roadside drainage ditch near Privateproperty (allegedly) not drainingproperly

Investigation finds ditch to functionadequately; no County action required

19970511 4735 200th St SW#A208 Lynnwood98036

Private property yard showing standingwater due to elevation of property and(perhaps) faulty detention pond

No County action required; see PDS re:detention pond issues; recommendedpermanent sump pump and/or raisinghouse/property

19970545 None stated Water standing at intersection as runofffrom 121st St. SW does not flow toexisting catch basin after intersectionimprovements

Placed on Potential Project list with highranking; to be placed on ConstructionProject list for 98

19970573 Sno. Co. P.D.S. Private property flooding due (perhaps)to undersized culvert after increasedflow from development

Project to be rated for potential; no Countyaction required (resolution and problemnot quite clear)


Private property driveway flooding asdrainage ditch along frontage has noproper outlet

Ranked as Potential project, with lowscore (31 of 85); not likely to be fixed soon

19980027 10430 Rosewood AveEverett 98204

Private property basement flooding fromnearby creek (possibly) being backedup by undersized culverts

Investigation unable to determine exactcause; culverts occur on Private property;no County action required; recommendedto consult civil engineer

19980056 9502 19th Ave SEEverett 98208

Private properties flooding as they liealong natural drainage course andadjacent wetland area

Natural occurrence; no benefit to divertingcourse; no County action required; seePDS re: future development concerns

19980080 9730 Sharon DrEverett 98204

Private property yards showing standingwater (perhaps) due to increased flowfrom nearby development

Investigation showed catch basins to beadequate; no County action required;recommended alternative drainage andcontacting PDS re: permitting issues w/development

19980107 1916 S. Lake StickneyDr. Lynnwood 98037

Private property showing standing waterunder house as lies within naturaldrainage bowl for area

Natural occurrence; no County actionrequired; alternative drain systemsrecommended


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19980120 9600 15th Ave NESeattle 981152212 Private property yard showing standingwater as lies in natural drainage coursefor area; development may also beaffecting

Natural occurrence; developmentdrainage currently not regulated; noCounty action required; recommended toconsult PDS re: permitting issues w/development

19980203 3317 121st St SWLynnwood 98037

Private property yard showingincreasing standing water, perhaps dueto water leak

Investigation found no drainage systemdefects; no County action required;recommended to consult water companyre: water leak

19980206 10202 Montana RdEverett 98204

Drainage ditch running through Privateproperty not properly functioning due todebris

Private system; no County action required

19980207 1028 136th St SWEverett 98204

Private property driveway eroding aswater passes over cracked cul-de-sac

Service Request sent to RoadMaintenance to repair driveway

19980236 1505 N. Lake StickneyDr Lynnwood 98037

Private property gravel road beingsaturated with water (supposedly) dueto nearby development; resident wishesto pave road

County portions of drainage systemchecked/scheduled for cleaning; Privatesystems not regulated; recommendedadditional drainage/ contact civil engineer/PDS re: road paving

19980240 10104 19th Pl WEverett 98204

Private property yards/crawlspacesaffected by undersized drainage system(swale)

Private system; no County actionrequired; recommended additionaldrainage; see PDS re: permitting for swalework

19980312 6121 NE 175th St A202 Kenmore 98028

Resident concerned with possibleimpact to Private property from newlyinstalled culvert outletting thereon;development to increase flow

Property lies within natural drainagecourse; County cannot re-route naturaldrainage for possible Private profit; noCounty action required

19980350 10029 Montana Rd

Everett 98204

Public road showing standing water due

to blockage in driveway-area culvert;water blocks one lane and driveway

Service Request sent to Road

Maintenance to unplug culvert

19980380 2830 York Rd Everett98204

Water sheetflowing from Countywalkway onto Private propertydriveway/front yard due to non-functioning catch basin

Service Request sent to RoadMaintenance to work on catch basin neardriveway to move water into drainagesystem

19980382 None stated Public road (Russell Way) and collateralApartment flooding (see problem19970227)

Complex issue; forwarded to CapitolImprovement section of Surface Water toplace on 6 year CIP list

19990052 3526 121st St SWEverett 98204

Basement apartment flooding fromplugged drain pipe and frontagedrainage ditch

Service Request sent to RoadMaintenance to unplug pipe and drainageditch

19990075 10725 WashingtonWay Everett 98204

Private property back yard/crawlspaceflooding as catch basin does not drain

System designed for infiltration, with nodrainage outlet; increased standing water

due to heavy rains; problem ranked (low)as Potential Project

19990113 2503 122nd St SWEverett 98204

Private property yard showing standingwater due to increased runoff fromnearby development and various landfillfrom grading for swimming pool

Private system; no County actionrequired; recommended to remove fill forwater to pass; continue to work withbuilder to resolve issue, and/or escalate toMBA/PDS


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19990121 701 105th St SWEverett 98204 Private property yard/crawlspaceshowing standing water from increasedflow due to development and naturaltopography

Service Request sent to RoadMaintenance to clean drainage system/ask City of Everett to clean theirs;alternative drainage recommended

19990124 522 94th St SWEverett 98204

Private property front/side yardsflooding following construction ofChallenger Elementary School

School is property of City of Everett; noCounty action required; alternativedrainage recommended

19990247 10725 WashingtonWay Everett 98204

Resident wishes to uncover closeddrainage system for repairs; wantsCounty to assess flood potential toneighbors in doing this

County gave recommendations for repairswhich allow for infiltration, to mitigatedownstream flow

19990250 1709 - 105th St SWEverett 98204

Private property showing water backupfrom neighbors portion of easement notbeing properly maintained

County sent letter to neighbor, statingeasements/restrictions in plat allow nograding/filling of drainage easement;

continue to work w/ neighbor, and/orescalate to DRC

19990307 None stated Public roadway and Private property(2722 128th St SW) flooding due toplugged culvert

Service Request sent to RoadMaintenance to unplug culvert

20000015 927 Center Rd Everett98204

Private property drainage problemspersist (see problem 19970511)

Service Request sent to FacilityMaintenance Group to clear yard wastefrom biofiltration swale adjacent toproperty; recommended grading of yard

20000058 Sno. Co. RoadMaintenanceSnohomish

Road Maintenance received complaintthat cross culvert under Ash Way notfunctioning

County portion cleared, problem mayoriginate downstream, out of right-of-way;SWM to observe problem and rank asPotential Project, if necessary

20000059 Sno. Co. Road

MaintenanceSnohomish

Citizen reports that Center Road shows

water problem; needs ditching

Further ditching not needed; no damage

to road evident, and would drain adjacentwetland areas

20000065 9022 8th Pl W Everett98204

Private property yard showing standingwater as drainage backs up due toneighbor blocking catch basin withdebris

Private property; no County actionrequired; recommended resolving withneighbor and/or escalating to DRC; also,alt drainage recommended

20000192 13432 MukilteoSpeedway Lynnwood98037

Privately-owned business flooding dueto runoff from Public road

Service Request sent to RoadMaintenance to grade shoulder of road,reducing runoff

20000228 12414 Highway 99 S.Everett 98204

Resident (of Empire Industrial Park)expresses concern over potential waterissues from ditch being built by adjacentproperty owner

Private system; no County actionrequired; recommended to flushinterceptor drain to ensure properfunctioning; if appeal for rate reduction isfiled, SWM will inspect stormwater

detention system20000238 Sno Co right-of-way

UseRequest to vacate portion of AdmiraltyWay

Surface Water Management has noposition regarding the petition to vacatethe subject Right-of-Way

20000259 3320 121st St SWLynnwood 98037

Resident wishes to alleviate surfacewater flow which renders certain portionof Private property unusable

Portion of property may be a wetland;resident would be required to preserve it;see PDS re: requirements for work inwetlands


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20010005 13600 26th Pl. W.Lynnwood 98037

Flooding of roadway occurring due toundersized culvert

Culvert to be replaced with pipe ofadequate size; new flow to system to beaddressed; road scheduled to be paved in2001 - project to be constructed beforepaving project begins

20010026 Sno. Co. PW Sr PermitCoordinator

WSDOT requests to turn back portion ofstate right-of-way to County by CountyTurnback Agreement 1-0146; pleaseidentify drainage concerns

County identified that ditches needed tobe cleaned; should request of DOT beforeaccepting turn back



No concerns identified; accepted



No concerns identified; accepted

20010034 12221 Airport RdEverett 98204

Public road flooding near entrance ofApartment complex due to blocked pipeand plugged curb outlet gap

Private system; no County actionrequired; recommended to clean systemand unplug gap, allowing curb-side waterto drain away

Previous Studies

A portion of the North Tributary HEC-RAS model was developed using data from the112th Street SW/SE Hydraulic Report(R. W. Beck, 1999). This report was prepared aspart of the Countys design efforts to improve 112th Street SW southwest from SR 99 to

3rd Avenue SE by widening the road and improving drainage and water quality. Thestudy included a HEC-RAS model of the Swamp Creek Tributary crossing 112th StreetSW near the North Meadow Apartments. Survey of a culvert crossing 115th Street SWobtained for the 112th Street study was also used to develop the North Tributary model.

The reach of the unnamed tributary downstream of the West Tributary was studied in theRussell Way Flooding Analysis (Otak, Inc., 2001), as part of the Snohomish County SpotDrainage Program. Otaks study analyzed the area immediately downstream of theWest Tributary modeled in this DNR. Hydrologic and hydraulic models were used tostudy flow through the culverts from the intersection of Russell Way and Alexander Roadto the culvert crossings beneath Russell Way, just south of the Max Ford CraneCompany and east of SR 99. Survey of topography and drainage structures performedfor this project supplemented survey data in the development of the HEC-RAS models.


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B3.3 HEC-RAS Development and ResultsThe purpose of the HEC-RAS modeling was to:

Develop FTABLEs for input to the HSPF model.

Evaluate culvert inadequacies and channel overtopping along the North Tributary,

the West Tributary, and Swamp Creek reaches for predicted existing and futureflows.

Analyze potential Capital Improvement Program (CIP) projects that would reduce thepredicted flooding.

B3.3.1 Existing Condition Model

The extent of the HEC-RAS modeling was defined at a basin meeting with the County onAugust 20, 2001. The basin encompasses two tributaries of Swamp Creek and a reachof Swamp Creek extending from the Lake Stickney outfall to Manor Way. The HEC-RASmodels cover 0.71 mile of the North Tributary, 0.71 mile of the West Tributary, and 0.32mile of Swamp Creek. Figures B3-1 through B3-3 provide schematics of the three HEC-

RAS models.A HEC-RAS model, previously developed for the 112th Street SW/SE Final HydraulicReport(R. W. Beck, 1999), was used to develop the North Tributary model. Thepreviously developed model extends from upstream of the SW 112th Street crossing toapproximately 230 feet downstream of SW 112th Street. As part of this study, channelcross-sections and culvert information were also obtained for the culvert crossing at SW115th Street. This information and the existing model were added to the North TributaryHEC-RAS model.

B3.3.1.1 Hydraulic Structures

Data for the hydraulic structures were developed from field survey information collectedas part of this project. A total of 19 culverts, two driveway bridges, and two in-line weirs

are located along the three reaches within the North Swamp Creek Subbasin and areincluded in the model.

Six culvert crossings and two in-line weirs are on the North Tributary, eight are culvertcrossings are on the West Tributary, and two driveway bridges and one culvert crossingare on Swamp Creek.


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B3.3.1.2 Channel Cross Sections

Channel cross sections were input into the HEC-RAS models from the survey datacollected for this project. Figures B3-1 through B3-3 show the locations where crosssections of the streams were surveyed to provide data for input into the hydraulicmodels. The river station numbers used in the models are also shown on the figures.

Table B3-2 lists the HEC-RAS cross sections used in the three models. This alsoincludes the locations (Figure B3-3) and river stations of stream cross sections surveyedfor the previous project (R. W. Becks 1999 112th Street SW/SE Final Hydraulic Report)that were input into the hydraulic model for North Tributary. The HEC-RAS crosssections in the model are listed in Table B3-2.

Surveyed cross sections were extended using the City of Everett and Alderwood WaterDistrict and City of Everett topographic mapping with five-foot contours if the crosssection was not wide enough to encompass the floodplain and contain the flow. Somecross sections were added to the model by interpolating between two known crosssections. Though not based on actual survey information, these additional crosssections help improve model results in areas with relatively steep water surface profiles,or in areas in which channel or overbank conditions change significantly between the

surveyed cross sections.

B3.3.1.3 Boundary Conditions

Normal depth was used as an upstream and downstream boundary condition for thethree HEC-RAS models. The program calculates a normal depth for each storm eventbased on the user-entered energy slope. Average channel slopes, determined using thesurvey data, were used to estimate the energy grade slopes to calculate normal depth.

B3.3.1.4 Mannings Roughness Coefficients

Mannings roughness coefficients for natural channels were determined fromobservations made during field reconnaissance. Natural channel roughness coefficients

were developed based on Roughness Characteristics of Natural Channels (Barnes,1967). Hydraulic structures were assigned a roughness coefficient as described in theHydraulic Modeling Protocols in the separately-bound Drainage Needs ReportsProtocols.

B3.3.1.5 FTABLE Development

FTABLEs used in HSPF describe the stage-discharge-area-storage relationship of thedrainage system and represent flow routing (Appendix A3). The HEC-RAS model for theNorth Tributary existing conditions was used to develop two FTABLEs for that tributaryand the HEC-RAS model for the West Tributary existing conditions was used to developfour FTABLES for that tributary in accordance with the procedures defined in theHydraulic Modeling Protocols. The FTABLEs represent the hydraulic routing in the

stream reaches through six subbasins. The flows used in HEC-RAS for FTABLEdevelopment encompassed flows well below the 2-year event and well above the 100-year event.

The upstream and downstream limits (extents) of the FTABLEs are described inTable B3-3.


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River Station Culvert No. Cross Section Source

-50 Offset of Cross Section 0

0 Surveyed Cross Section ED10699

26 1 Survey Data


100 Interpolated

150 Interpolated

200 Interpolated

250 Interpolated

300 Interpolated

350 Interpolated

400 Interpolated

450 Surveyed Cross Section EC11062

466.17 Interpolated482.34 Interpolated

498.51 Interpolated

514.68 Interpolated

530.85 Interpolated

547.02 Surveyed Cross Section EC11071

553.02 Surveyed Cross Section ED10744

564.02 2&3 Survey Data

578.02 Surveyed Cross Section ED10733

596.85 Interpolated

615.68 Interpolated

634.51 Interpolated

653.34 Interpolated

672.17 Interpolated


718.5 4&5 Survey Data



801.5 Weir 1 Survey Data

820

855.2 Interpolated

890.4 Interpolated

925.6 Interpolated

960.8 Interpolated



1127.49 Interpolated



1258.98 Offset of Cross Section 1271

Table B3-2 (continued)

North Tributary

Model Cross Sections

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December 2002


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1344.98 6 Survey Data1355.98 Surveyed Cross Section EC11014

1435.48 Weir 2 Surveyed Cross Section



1522.4 Interpolated















2112.1 Interpolated

2149.93 115th Street Culvert Survey

2192.43 7 115th Street Culvert Survey



2355.93 115th Street Culvert Survey2405.93 Interpolated















3155.93 112th Street Project



December 2002


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3369.53 112th Street Project3452.53 8 112th Street Project





37 Offset of Cross Section 0

38 Interpolated

39 Interpolated

40 Interpolated

41 Interpolated

42 Interpolated

43 Interpolated

44 Interpolated

45 Interpolated

46 Interpolated


73 1 Survey Data


122 2 Survey Data





332 Offset of Cross Section 322358 3









526.47 Interpolated








West Tributary


December 2002


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700.647 Interpolated720 Surveyed Cross Section EC11087

800 Interpolated

880 Interpolated



1127.5 Interpolated




1330 4&5 Survey Data





1446 6 Survey Data



1583 7 City of Everett topography



1795.3 Interpolated







2318 8 Surveyed Cross Section














2585.9 Interpolated


December 2002


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2980.7 Interpolated






3189 9 Surveyed Cross Section







3405.02 Surveyed Cross Section EC104593408.02 Surveyed Cross Section EC10450








3748.02



53.5 1 (bridge) Survey Data



146.4 Interpolated

228.8 Interpolated

311.2 Interpolated

393.6 Interpolated

Swamp Creek


December 2002


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476 Surveyed Cross Section EC10237502 2&3 Survey Data



577.5 Interpolated

611 Interpolated

644.5 Interpolated


752.33 Interpolated

826.66 Interpolated




1041.99 4 Survey Data












1707.23 Interpolated1736.03 Surveyed Cross Section EC10303


December 2002


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Table B3-3Physical Extents of FTABLEs Generated from HEC-RAS

FTABLE Extent

HSPF Reach Location Downstream Control

DownstreamRiver Station

(ft)

UpstreamRiver Station

(ft)

R500 North Tributary from Center Rd.to 115th St.

Center Rd. Culvert -50 2226

R505 North Tributary from 115th St. to112th St.

115th St. Culvert 2226 3548

R420 West Tributary from 128th Pl.SW to Gibson Rd.

128th Pl. SW Culvert 0 1464

R425 West Tributary from Gibson Rd.to 122nd St. Culvert

Gibson Rd. Culvert 1464 2345

R430 West Tributary from 122nd St.Culvert to 119th St. Culvert

122nd St. Culvert 2345 3158

R435 West Tributary from 119th St.Culvert to Center Rd.

119th St. Culvert 3158 3748

Notes:

1. FTABLE depth computed at downstream cross section.

2. FTABLE volume and area computed between downstream and upstream extent.

B3.3.1.6 Existing and Future Conditions Flood Frequency

Flows used in the model were established from the HSPF hydrologic analysis andconsist of the 2-, 10-, 25-, and 100-year recurrence frequencies for both existing andfuture land use conditions. These flows were entered into the HEC-RAS models atseveral locations to represent changes in flow along the stream due to the contributionsof the downstream drainage basins. In general, the flow calculated for a subbasin wasentered into HEC-RAS at the upstream end of the subbasin.

Table B3-4 shows the existing and future condition peak discharge rates used in theHEC-RAS modeling. The existing and future conditions flood frequency analysis isdescribed in Appendix A3.

B3.3.1.7 Additional Modeling Assumptions

The following assumptions were made while developing the HEC-RAS models:

Surveyed pipe material information obtained for Culvert 3 on the North Tributaryindicate corrugated metal pipe (CMP) at the upstream end and concrete at thedownstream end. A Mannings n coefficient value for CMP was used in accordancewith the Hydraulic Modeling Protocols.

The driveway cross section for Culvert 2 on the West Tributary was developed usinga single surveyed point. The driveway was assumed to be 9 feet wide at the culvertcrossing.


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2-Year Q

(cfs)

10-Year Q

(cfs)

25-Year Q

(cfs)

100-Year Q

(cfs)

2-Year Q

(cfs)

10

R500 3548 Upstream of SW 112th St. 23.5 53.3 72.5 90.0 24.8

R505 2226 SW 115th St. 21.8 41.6 55.2 80.1 23.2

R420 25557 Center Rd. 3.9 5.4 7.3 12.9 4.5

R425 22867 119th St. 4.6 7.0 9.3 15.0 5.5

R430 19119 122nd St. 6.3 10.4 13.4 19.6 7.4

R435 18156 Gibson Rd. 9.2 15.3 19.2 26.0 10.5

R555 16314 Lake Stickney outfall 60.1 110.4 148.2 225.5 70.5

cfs = cubic feet per second

North Tributary

West Tributary

Swamp Creek

Table B3-4

HEC-RAS Flow Model Input for Existing and Future Land Use Conditions for North Sw

HSPF

Reach

River

Station

(ft) Location

Existing Land Use Conditions Futur


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Survey information for Culvert 7 on the West Tributary indicates high-densitypolyethylene (HDPE) pipe at the upstream end and concrete pipe at the downstreamend. An average Mannings n coefficient value was used.

During field reconnaissance visits, project staff observed several small beaver damsalong the Swamp Creek reach downstream from Lake Stickney. Although the dams

potentially could impact flow through the channel, they were not consideredpermanent features and, therefore, are not included in the hydraulic model.Similarly, a wood crossing constructed of three logs laid across the Swamp Creekchannel was not included in the model.

A large beaver dam at the outlet of Lake Stickney could restrict flow from the lake.The dam was located but not dimensioned by survey. The Swamp Creek HEC-RASmodel ends downstream from the beaver dam at a natural cross section. During aJune 2001 field visit, the beaver dam was restricting the outlet to the lake, causingthe lake levels to rise 3 feet higher than normal. During a subsequent visit inNovember 2001, the beaver dam was no longer effective and flow was going throughand around the dam. There were remnants of previous dams in the area betweenthe lake outlet and Jefferson Way. Field staff spoke to the property owner of the

bridge crossing upstream and he showed staff the location of another substantiallysized beaver dam upstream of his property. He had been taking the dam apart atevery opportunity and had also removed debris from the upstream side of theculverts at Jefferson Way. Similar to the small beaver dam, the large beaver damwas not considered a permanent structure and, therefore, is not included in themodel.

There are two in-line weirs along the North Tributary reach. One weir controls flowout of the wetland upstream of SW 115th Street. The second weir controls flow fromthe pond at the condominiums on Admiralty Way north of the intersection ofAdmiralty Way and Center Road.

B3.3.2 Model Results and Problem Identification with ExistingConditions Flows

Water surface profiles were computed for 2-, 10-, 25-, and 100-year peak dischargerates for the existing land use conditions. Problem areas in the HEC-RAS models arethose locations where culverts have insuuficient capacity to convey flow to thedownstream side of the road (i.e. road flooding occurs). Problem areas also includeareas where the flow goes over the channel banks and then floods property. HEC-RASmodel results are summarized in Table B3-5. This table compares water surfaceelevations to road flooding elevations for all culverts in the model. This table also listsculvert identification and location, culvert size and material, river station, floodingelevation, and water surface elevations at the upstream end of each culvert in thestream system for the 2-, 10-, 25-, and 100-year events under existing flow conditions.

Potential property flooding identification is based on anecdotal information and a reviewof the available topography mapping in comparison to the water surface elevations. Itwas assumed that if the water surface elevation is equal to the topographic elevationshown in the vicinity of a property or structure, flooding may occur.


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The North Tributary HEC-RAS model results indicate that under existing land useconditions, one culvert crossing begins to flood at the 2-year event, and one channelbegins to flood at the 10-year event. In addition, one culvert crossing begins to flood atthe 25-year event and two culvert crossings begin to flood at the 100-year event. Privatedriveway and yard flooding could potentially be caused by the overtopping of twodriveway culverts on the North Tributary. In addition, the 112th Street SW/SE Final

Hydraulic Report(R. W. Beck, 1999) notes the occurrence of flooding at multi-dwellingunits along the North Tributary between 112th Street SW and 155th Street SW, which isverified by the model showing overtopping of the channel downstream of 112th StreetSW and confirmed for the DNR study by County staff observations that this area floodsevery 3 to 5 years. However, there were no documented drainage complaints along theNorth Tributary from 1996 to 2001. According to this report, and based on conversationswith local residents, water in the form of shallow sheet flow overtops the 115th StreetSW culvert. Road flooding was not reported as resulting in property flooding becausethe culvert crossing is at a low point in the road profile and surrounding properties are athigher elevations.

The West Tributary HEC-RAS model results indicate that, under existing land useconditions, two culvert crossings cause flooding during the 10-year event, four culvertcrossings begin to flood during the 25-year event, and one culvert crossing begins toflood at the 100-year event. Flooding of driveway culverts along the West Tributary isexpected to cause minor private driveway and property flooding at three locations.Along the West Tributary, flooding was reported at properties north of Gibson Road.County staff have observed flooding at the Alexander Road/Russell Way crossings anda nearby apartment complex. During a field reconnaissance visit in June 2001, projectstaff spoke with the owner of the property at the southwest corner of York and Alexanderalong the West Tributary reach. He mentioned that during the rain-on-snow event a fewyears ago, the stage in the stream rose to 2 feet into his yard and the driveway culvertflooded. This is consistent with the modeling results.

The Swamp Creek HEC-RAS model results indicate that under existing land use

conditions, one driveway bridge flooded during the 10-year event. Model results predictthat the width of the flooded area ranges from approximately 70 feet during the 10-yearevent to approximately 300 feet during the 100-year event. Flooding in this area wouldlikely impact the public roadway and private property. A drainage complaint filed in 1997(Service Request Number 19970207) reported private property flooding and housedamage. However, surveyed finished floor elevations of private properties near the LakeStickney outfall are all above the 100-year elevation calculated at the upstream end ofthe Swamp Creek HEC-RAS model.

In addition, a property owner downstream of the lake reported chronic problems withbeaver dams and debris clogging the culverts crossing underneath Jefferson Way. Thisresults in property flooding although the roadway does not flood.

During a field visit in June 2001, staff members spoke with the property owner of thedriveway bridge crossing at 1371 S Manor Way between Jefferson Way and the outlet toLake Stickney. He said that during the rain-on-snow event of 1999, the stream levelrose to within an inch of his doorstep. He also mentioned that during summer, thechannel reach between the driveway bridge and Jefferson Way dries up. The propertyowner said that about 35 to 40 years ago, the stream flowed behind, instead of in front,of his house. This is consistent with the contour mapping and the depression in the areasouth and east of his property. In November 2001, the flow under the bridge wasobserved to be just below the low chord of the bridge. The flow at the time was


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estimated by the staff to be between 40 and 60 cfs. The calculated water surfaceelevation appeared to be consistent with the field observation.

Figure 8-1b shows the location of each existing flooding problem predicted by thehydraulic analyses.

B3.3.3 Model Results and Problem Identification with FutureConditions Flows

Table B3-5 summarizes the water surface profiles computed for future land use conditionsat 2-, 10-, 25-, and 100-year peak discharge rates. Table B3-5 compares water surfaceelevations to road flooding elevations for all modeled culverts. This table lists culvertidentifications and locations, sizes and materials, river stations, flooding elevations, andwater surface elevations at the upstream end of each culvert in the stream system for the 2-,10-, 25-, and 100-year storm events under future flow conditions.

Overall, the HEC-RAS models predicted that, in the future, flooding elevations wouldslightly increase at nearly all culvert crossings and that flooding frequencies wouldincrease at several locations. Three new flooding problems were predicted to occur forfuture land use conditions.

The North Tributary HEC-RAS model results indicate that, under future land useconditions, one culvert crossing begins to flood at the 2-year event, one culvert crossingand one channel begin to flood at the 10-year event, and two culvert crossings begin toflood at the 100-year event.

The West Tributary HEC-RAS model results indicate that under future land useconditions, four culvert crossings are flooded during the 10-year event, three culvertcrossings begin to flood during the 25-year event, and one culvert crossing begins toflood at the 100-year event.

Results of HEC-RAS modeling of the Swamp Creek reach indicate that, under future

land use conditions, one driveway bridge floods during the 10-year event, one drivewaybridge floods during the 25-year event, and one culvert crossing floods during the 100-year event.

Figure 8-1b shows the location of each future flooding problem predicted by thehydraulic analyses.

B3.4 CIP Alternatives

The majority of the CIP projects developed for the North Swamp Creek Subbasin areconveyance improvements that involve culvert upgrades. Other projects include bridgereplacements and berm constructions. This section describes the design criteria and

solution development approach used to design these culvert and bridge upgrades toalleviate flooding problems. The locations of problems are shown in Figure 8-1c and aresummarized on Table 8-1c. This section supplements the standards in Section 7.0 ofthis report. Descriptions of additional design criteria, procedures, and assumptions areincluded in Appendix B1.

All of the culvert improvements need to be designed to meet fish passage requirements.Ten culverts need to be upgraded. Seven of the culverts were designed in accordancewith the No Slope Option as defined in Fish Passage Design at Road Culverts (WDFW,


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1999). Three culverts were sized using the Stream Simulation Option as defined inWDFWs fish passage design guidelines (1999).

B3.4.1 CIP Alternative 1

The objective of CIP Modeling Alternative 1 for the North Swamp Creek Subbasin was toaddress flooding problems along the North Tributary, West Tributary, and main stem ofSwamp Creek downstream of Lake Stickney through conveyance improvements. Thedevelopment of Alternative 1 is described in Section 9.2.3.

B3.4.1.1 CIP Alternative 1 Hydraulic Model Changes

CIP Modeling Alternative 1 for North Swamp Creek Subbasin generally addressesproblems within the basin by installing larger culverts at flooding problem locations toincrease the capacity of the existing conveyance system and reduce flow velocities inthe culverts. This alternative includes upgrading two culverts on the North Tributary,seven culverts on the West Tributary, and one culvert replacement on the main stem ofSwamp Creek. All 10 of these culvert replacements were designed to meet the WDFWfish passage design criteria although none were identified as fish passage problems in

the habitat analysis. The culvert replacement on the main stem of Swamp Creek atJefferson Way was previously designed and was approved for construction on May 15,2002. The design for this culvert replacement was used in the analysis for thisalternative.

In addition to the culvert upgrades, this alternative also includes a proposed flood controlberm approximately 900 feet in length on the North Tributary downstream of 112thStreet SW to alleviate known private property flooding.

This alternative also includes raising Russell Way and constructing an earthen bermapproximately 300 feet in length, which are projects incorporated into the DNR studyfrom the Russell Way Flooding Analysis Report(Otak, 2001). This project is locateddownstream of the West Tributary and was not included in the HEC-RAS model.

In the main stem of Swamp Creek downstream of Lake Stickney, Railspan bridges wereused to replace two clear span bridges at the crossings upstream and downstream ofJefferson Way. The proposed Railspan bridges have higher low chord elevations thanthe existing bridges to provide additional conveyance capacity.

The three HEC-RAS models were modified with the conveyance improvements asdescribed above and as shown on Table B3-6. The HEC-RAS models for the NorthTributary and the West Tributary were used to develop new FTABLEs for the HSPFmodel. The new FTABLEs were inserted into the HSPF input file. The HSPF modelwas rerun, and the resulting flows were used to create an updated flow frequencyanalysis. These flows, shown on Table B3-4, were then input to the HEC-RAS modelsfor the final sizing of the solutions and to evaluate the effects of the conveyanceimprovements on downstream flooding and flows. More details on the HSPF analysiscan be found in Appendix A3.

Note that under existing conveyance conditions, the private driveway downstream of12th Avenue W floods for the 100-year event and was identified as a problem in Section8.0, but was not selected for analysis. However, during the alternative analysis,upstream conveyance improvements caused downstream flow to increase. This causedthe flood frequency at this location to increase such that a 25-year event would causeflooding. As a result, a culvert improvement was also developed for this location.


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The specific CIP projects included in CIP Modeling Alternative 1 are summarized on Table9-2. This table summarizes each modeled CIP project and its benefits. Figure 9-1c showsthe location of each project.

B3.4.1.2 Model Results with Future Conditions Flows

The results of the HEC-RAS models using the conveyance improvements that compriseCIP Modeling Alternative 1 are presented in Table B3-7. This table compares the watersurface elevations at the culverts and bridges in the system for the existing conveyancesystem under existing and future land use conditions with CIP Modeling Alternatives 1and 2. In addition to listing the 2-, 10-, 25-, and 100-year water surface elevations forthe new conveyance system, the table shows the size and material of the existing andproposed culverts and bridges.

Improving conveyance systems by increasing capacity can cause a reduction infloodplain storage and consequently increase downstream flow rates. By increasingculvert sizes to alleviate flooding problems, flood storage is reduced and downstreamflows are increased. The flow increases for this alternative are shown in Table 9-3c. Asstated in the previous section, one additional culvert upgrade was necessary on the

North Tributary as a result of the flow increases from improved conveyance capacity attwo culvert locations and the installation of the berm.

The upsizing of culverts and loss of storage causes slight increases in downstreamwater surface elevations at some locations when compared to water levels under futureland use conditions. These increases are less than 1 foot and do not cause anyadditional downstream flooding problems. The HEC-RAS model results generally showa decrease in water surface elevations throughout the system for the 2-, 10-, 25-, and100-year events between the future land use results and the CIP Modeling Alternative 1results.

Ultimately, this alternative was not recommended because it does not provide anymitigation for the increase in downstream flows caused by the proposed conveyance

improvements.

B3.4.2 CIP Alternative 2

The objective of CIP Modeling Alternative 2 for the North Swamp Creek Subbasin was toaddress flooding problems along the North Tributary, West Tributary, and main stem ofSwamp Creek downstream of Lake Stickney through conveyance improvements, and toprovide stormwater detention storage to help reduce the increases in peak flow rateswithin the subbasin resulting from the conveyance improvements, loss of storage, andfuture land use changes. The development of Alternative 2 is described in Section 9.2.3.

B3.4.2.1 CIP Alternative 2 Hydraulic Model Changes

CIP Modeling Alternative 2 for North Swamp Creek Subbasin includes the 14conveyance improvements proposed in CIP Modeling Alternative 1, as well as oneproposed detention facility. The purpose of adding the detention facility is to reducepeak flows resulting from future development and increased downstream flows resultingfrom the upgraded culverts. It was hoped that the detention facility might decrease flowssuch that the number of culvert replacements required in CIP Modeling Alternative 1could be reduced. However, the detention provided by this facility is not adequate toeliminate the need for replacing culverts that have been identified as flooding problems.


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The detention facility would also provide water quality treatment. The detention facilityincluded in this alternative is described in Section 9.2.3 and Appendix A3.

Three detention sites were initially considered for this subbasin. One was located oneach of the three tributaries that were modeled: North Tributary, West Tributary, and themain stem of Swamp Creek. Proposed off-line detention facilities were located

upstream of Center Road in the North Tributary of Swamp Creek and upstream of thenorthwest of the intersection of Alexander Way and Russell Way in the West Tributary.An in-line detention facility was located in the overbank area of the channel upstream ofJefferson Way on the main stem of Swamp Creek. These detention facilities wouldattenuate flows prior to discharging them downstream of the facility. However, duringthe alternative development process, the initial review of the model results showed thatthe proposed detention facilities on the West Tributary and the main stem of SwampCreek were not effective in decreasing downstream flows. Therefore, only the detentionfacility on the North Tributary was included in CIP Modeling Alternative 2. Thisalternative development procedure is further described in Section 9.2.3 and AppendixA3.

The HEC-RAS models were modified with the conveyance improvements as described

under CIP Modeling Alternative 1 and shown on Table B3-6. The updated FTABLEsgenerated as described for CIP Modeling Alternative 1 for the North Tributary and theWest Tributary were entered into the HSPF model that included the detention ponds torecalculate the frequency analysis. The HSPF model setup is described in SectionA3.5.6.1. The revised flows, shown on Table B3-4, were then entered into HEC-RAS toevaluate the effects of the conveyance and detention improvements on downstreamflooding and flows. More details on the HSPF analysis can be found in Appendix A3.

The specific CIP projects included in CIP Modeling Alternative 2 are indicated in Table9-2. This table summarizes each modeled CIP project and its benefits. Figure 9-1cshows the location of each project.

B3.4.2.2 Model Results with Future Conditions Flows

The results of the HEC-RAS models using the conveyance improvements and thedetention facility that comprise CIP Alternative 2 are presented in Table B3-7. This tablecompares the water surface elevations at the culverts in the system for the existingconveyance system under existing and future land use conditions as well as for CIPAlternatives 1 and 2. In addition, the table shows the sizes and materials of the existingand proposed culverts.

The results show that the benefit of the detention pond was to reduce peak flows in thesection of the North Tributary adjacent to the proposed pond location. The flows wereslightly reduced over the Alternative 1 flows because storage lost from the system due toconveyance improvements was regained by incorporating the proposed pond storage.The flow changes are shown on Table 9-3c and summarized in Section 9.2.3

Additionally, the detention pond aids in improving water quality along the North Tributary.

The upsizing of culverts and loss of storage causes slight increases in downstreamwater surface elevations at some locations when compared to water levels under futureland use conditions, as also shown in the CIP Modeling Alternative 1 results. Theseincreases are less than 1 foot and do not cause any additional downstream floodingproblems. The HEC-RAS model results generally show a decrease in water surfaceelevations throughout the system for the 2-, 10-, 25-, and 100-year events between thefuture land use results and the CIP Modeling Alternative 2 results. The HEC-RAS


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results for CIP Modeling Alternative 2 vary slightly from CIP Modeling Alternative 1. Theeffect of the proposed pond is reflected in the flow changes and not in the water surfaceelevation changes.

After considering the model results, the cost estimates, and other factors, therecommended alternative is CIP Alternative 2. CIP Alternative 2 has a slightly higher

cost than Alternative 1, but is selected because of the additional benefits of offsettingsome of the increase in flow caused by the conveyance improvements and of providingimproved water quality.

B3.5 References

Barnes, H.H. 1967. Roughness Characteristics of Natural Channels. United StatesGeological Survey Water-Supply Paper 1849.

Otak. 2001. Russell Way Flooding Analysis. Prepared by Otak, Inc. as part of theSnohomish County Spot Drainage Program. July 2001.

R. W. Beck. 1999. 112th Street SW/SE Final Hydraulic Report(including 2000

supplement). Prepared by R. W. Beck, Inc. for Snohomish County.


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1

Attachment B3-1Additional Problem Areas Identified But Not Studied

(Swamp Creek North Subbasin)

Reach/Area Section/T/R Description Quantities Analysis Methodology

1 24, 28N, 4E inthe middle

Area between108th St. SW South104th St. SW onNorth, 1st Ave. SEon east and 7thAve. W. or theWest

3,000 ft. of roadside ditchand some pipe w/20 CBs2000 ft. of small channel

This will not be analyzedunder this contract.

2 24, 28N, 4E inthe SW

Mobile Home ParkNorth of 112th St.SW along 6th Ave.W.

700 ft. of roadsideditch/pipe system w/10CBs


3 23, 23N, 4E inSE

HEC-RAS model ofSwamp Creek fromHollow Dale Placeto South and Eastof Hwy. 99

Culvert at Hollow DalePlace 3 x sections1,100 ft. of channel 3 xsections1,200 ft. of channel 4 xsections500 ft. of channel 2 xsectionsAssume misc. 4 culverts 12 x sections


4 26, 28N, 4ENE & SE sections

HEC-RAS ofSwamp Creek fromEast of Hwy. 99 toSouth of 128th

1,000 ft. of channel 2 xsectionsCulvert under Center Road 3 x sections2,100 ft. of channel 7 xsectionsCulvert under Airport Rd. 3 x sections

1,500 ft. of channel 5 xsectionsCulvert under Gibson Rd. 3 x sectionsCulvert under 128

th 3 x

sections1,000 ft. of channel 3 xsectionsApprox. misc. 6 culverts 18 x sections


5a 35 28N, 4E NEand NW sections

HEC-RAS ofSwamp Creek fromSection Linethrough Lake

Stickney.

650 ft. of channel 2 xsectionsto Lake Stickney



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Attachment B3-1Additional Problem Areas Identified But Not Studied

(Swamp Creek North Subbasin)

Reach/Area Section/T/R Description Quantities Analysis Methodology

8b 26, 28N, 4ENW and SW sections

HEC-RAS model ofW. Fork of SwampCreek fromAlexander Road toManor Way justeast of Hwy. 99

channel through wetland 1 x sectionCulvert @ Russell Way 3sections350 ft. of channel 1 xsectionCulvert on Hwy. 99 3sections700 ft. of channel 2sections450 ft. pipe system onManor WayApprox. misc. 6 Culverts 18 x sections

This reach will not beanalyzed under thiscontract

9 35, 28N, 4E HEC-RAS of West

fork of SwampCreek from ManorWay just east ofHwy. 99 toconfluence w/mainfork

1,400 ft. of channel 4 x

sectionsCulvert under 136

thPl. SW

3 x sections1,050 ft. of channel throughwetland-FTABLE 2 xsectionsCulvert under Manor Way 3 x sections100 ft. of channel toconfluenceApprox. misc. 3 Culverts 9 x sections

This reach will not be

analyzed under thiscontract

10 27, 28N, 4ENE section

Local floodingproblem west of

Beverly Park Rd.and S. of 121 St.SW

100 ft. of ditch, 200 ft. ofstorm drain pipe with 4 CBs

and 500 more ft. of ditch

This reach will not beanalyzed under this

contract

11 26, 28N, 4E,SW section

Local flooding onAlexander Rd.between GibsonRd. and York Road

1,100 ft. of storm drain pipeand 9 CBs


12 26, 28N, 4ENW section

Water over CenterRd. West of MarinoAve.

Field work to find outletfrom wetland on the southand survey relative to 112

th

St. SW


13 35, 28N, 4ENE section

Local flooding on17th Ave. W. andN. Lake Stickney

Dr.

1,200 ft. of storm drainsystem w/9 CBs


14 36, 28N, 4ENorthwest

Intersection of AshWay and 137th St.SW floods

Locate outlet of system toLake 1,300 ft. of pipe.Survey pipes & CBs inintersection


swampcreek_ap_b3

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