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Grant Creek Restoration & Flood Control Project: 10-year Follow Up

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AMFM 2017 Annual Conference March 7th, 2017

Project Background

Design & Construction

Lessons Learned

Questions

Lower Project Limit at Clark Fork River Floodplain

Upper Project Limit at I-90

Project Background

Mullan Trail Subdivision

Resulted in lawsuit Homeowners Association implemented a fix

that experienced groundwater challenges Prompted Missoula County to initiate a

project through the US Army Corps of Engineers to find a solution

1997 Flood Event

Pre-project analysis showed significant 100-year flood impacts

Mullan Trail Subdivision 42 homes affected

Homes were being flooded

Pre-1997 flood construction Post-1997 flood construction

Aggradation was reducing flood conveyance

Culverts were significant barriers to fish passage

Severe erosion was occurring

Multiple project stakeholders resulted in project challenges!

City of Missoula State Highway Railroad Airport Area Large Undeveloped

Ranches Irrigation District Existing

Developments Interested

Developers

$4.2 M FEMA Pre-disaster Mitigation Grant was acquired by Missoula County for the project!

SUBMITTED!

Second Application All Electronic new for

FEMA Missoula County

Commitment and Funds Landowner

Easements/Approvals Mapped Property

Elevations Supported by Hydrologic

and Hydraulic Studies Benefit-cost Analysis

Required

Design and Construction - Grant Creek Project Reaches

Horseshoe Bend

Upper Grant Creek

Hiawatha Lake

Mullan Trail/Prarie Schooner

Clark Fork Confluence

The Creek was filling-in upstream of Highway 10 (West Broadway) Uppper Grant Creek Reach

Field measurements of the creek bed showed a rise in the bed elevation

?

The creek was losing its flood-carrying capacity

Cleaning of channel and culvert removal in Upper Grant Creek reach improved hydraulics and eased aggradation

Pepsi Co. Culverts... Removed By Mother

Nature!

Fish passage problems at West Broadway were addressed

Culvert replacement was designed to:

Reduce Flood Elevation Meet State and Federal Fish

Passage Criteria

Rehabilitation of existing culverts was not cost effective Replacing the culvert with natural bottom structures was implemented

Relative Cumulative Culvert Costs

Years

Rel

ativ

e C

osts

Culvert Replacement Costs

Culvert Rehabilitation

Long-Term Cost Savings Strategy

Chart1

10010

10520

11030

11540

12050

12560

13070

13580

14090

145100

150110

155120

160130

165140

170150

175160

180170

185180

190190

195200

200210

205220

210230

215240

220270

225280

230290

235300

240310

245320

250330

255340

260350

265360

270370

275380

280390

285400

290410

295420

300430

305440

310450

315460

320470

325480

330490

335500

340510

345540

Cumulative Open Bottom Culvert Cost

Cumulative Baffled Culvert Cost

Years

Relative Costs

Relative Cumulative Culvert Costs

Sheet1

11001001010

251051020

351101030

451151040

551201050

651251060

751301070

851351080

951401090

10514510100

11515010110

12515510120

13516010130

14516510140

15517010150

16517510160

17518010170

18518510180

19519010190

20519510200

21520010210

22520510220

23521010230

24521510240

25522030270

26522510280

27523010290

28523510300

29524010310

30524510320

31525010330

32525510340

33526010350

34526510360

35527010370

36527510380

37528010390

38528510400

39529010410

40529510420

41530010430

42530510440

43531010450

44531510460

45532010470

46532510480

47533010490

48533510500

49534010510

50534530540

Sheet2

Sheet3

Landowners in Horseshoe Bend Reach not ready to participate in the project

Horseshoe Bend Unnatural Channel Remains Pruyn Check Dam Remains (10 Year Commitment)

Post-project 100-year floodplain Hiawatha Lake and Mullan Trail Reaches

Hiawatha Lake Reach

Mullan Trail Reach

Analysis of groundwater/surface water interactions at Hiawatha Lake reach were key

Shallow groundwater contributed to historical Grant Creek flooding!

Sand Seams Were Eliminated When Hiawatha Lake Riparian Terrace Was Constructed

Addressing irrigation inputs to groundwater in the Hiawatha Lake and Mullan Trail reaches were necessary

Worked With Active Agriculture Entities to Provide More Flow Control

Minimized Waste Streams

Reduced Infiltration Sources

Established/Developed Riparian Corridor in the Hiawatha Lake, Mullan Trail and Prairie Schooner Reaches Used locally adapted

native plant species. Minimized exotic

plant colonization. Maximized Woody

Material. Minimized impacts to

Lower Clark Fork River trout- overflow weir

Improved waterfowl and other wildlife habitat.

Riparian Corridor Was Also Developed With Fish Passage Considerations

Mullan Trail Earthen Overflow Weir in

Operation


Horseshoe Bend

Upper Grant Creek

Hiawatha Lake



Channel Modifications in Prairie Schooner Reach Was Limited by Available Right-of-way

Channel construction did help landowners in the Mullan Road reach


Horseshoe Bend

Upper Grant Creek

Hiawatha Lake



Peak Flow Bypass engineered solution was required

Public Policy failures within governmental entities can happen (FEMA DFIRM mapping was wrong from the start)

Be Flexible - game changers (Hurricane Katrina) can occur Multiple Stakeholders can shape the final product public outreach is paramount

Lessons Learned

DFIRM mapping was INCORRECT, which led to poor decisions

Some recommended actions may have to wait (Dougherty Ranch at Horseshoe Bend, Pruyn

Check Dam, properties west of Mullan Trail subdivision) Natural solutions are preferred, but dont get trapped (Peak flow bypass structure enabled the

hydraulic solution)

Lessons Learned (cont.)

Surface and groundwater interconnection should be considered (Hiawatha Lake sand seam removal solved the Mullan Trail subdivision groundwater problems)

Project permitting adds considerable time and complexity

Lessons Learned (cont.)

Questions?

Slide Number 1Grant Creek Restoration & Flood Control Project: 10-year Follow UpSlide Number 3Slide Number 4Slide Number 5Slide Number 61997 Flood EventPre-project analysis showed significant 100-year flood impactsHomes were being floodedAggradation was reducing flood conveyanceCulverts were significant barriers to fish passageSevere erosion was occurringMultiple project stakeholders resulted in project challenges!$4.2 M FEMA Pre-disaster Mitigation Grant was acquired by Missoula County for the project!Design and Construction - Grant Creek Project ReachesThe Creek was filling-in upstream of Highway 10 (West Broadway) Uppper Grant Creek ReachCleaning of channel and culvert removal in Upper Grant Creek reach improved hydraulics and eased aggradationFish passage problems at West Broadway were addressedLandowners in Horseshoe Bend Reach not ready to participate in the projectPost-project 100-year floodplain Hiawatha Lake and Mullan Trail ReachesAnalysis of groundwater/surface water interactions at Hiawatha Lake reach were key Sand Seams Were Eliminated When Hiawatha Lake Riparian Terrace Was ConstructedAddressing irrigation inputs to groundwater in the Hiawatha Lake and Mullan Trail reaches were necessaryEstablished/Developed Riparian Corridor in the Hiawatha Lake, Mullan Trail and Prairie Schooner ReachesRiparian Corridor Was Also Developed With Fish Passage ConsiderationsDesign and Construction - Grant Creek Project ReachesChannel Modifications in Prairie Schooner Reach Was Limited by Available Right-of-wayChannel construction did help landowners in the Mullan Road reachDesign and Construction - Grant Creek Project ReachesPeak Flow Bypass engineered solution was requiredLessons LearnedLessons Learned (cont.)Lessons Learned (cont.)Questions?

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