FLOOD HYDROLOGY OF THE AND ITS TRIBUTARIES FROM WARM SPRINGS TO GARRISON A BASIS FOR REMEDIAL DESIGN

K. Mainzhausen, P.E B. Bucher, P.E.

October 3, 2013 Introduction

• Authors – Bill Bucher – PE, CDM Smith – Karin Mainzhausen – PE, CDM Smith – Karin Boyd – Geomorphologist, Applied Geomorphology, Inc. • Agencies – Department of Environmental Quality – Natural Resource Damage Program - Montana Department of Justice – Environmental Protection Agency • Other Consultants – Geum Environmental Consulting, Inc. – Vegetation Design – Tetra Tech, Inc. – TerraGraphics Environmental Engineering, Inc.

2 Flood Hydrology of the Clark Fork River and its Tributaries Montana AWRA 2013 Topics of this Presentation

• Background of Upper Clark Fork River Site • Remedial Action Objectives • Hydrologic Setting of Reach A • Mainstem Peak Flow Hydrology • Tributary Peak Flow Hydrology • Flow Duration

3 Flood Hydrology of the Clark Fork River and its Tributaries Montana AWRA 2013 Background

Clark Fork River Operable Unit (CFROU) • Part of the largest complex of Superfund Sites in the USA • Mine waste contamination from historic in the Butte -Anaconda region • It is estimated that the CFROU - Reach A will be an 12 to 15 year remediation effort • Reach A is approximately 45 miles long • It was subdivided into 22 phases

Flood Hydrology of the Clark Fork River and its Tributaries Montana AWRA 2013 4

CFROU Background

• Regulatory Framework – In 1981 - ARCO acquired property from Anaconda Copper Company – In 1983 - CFROU was listed NPL – In 2004 - Record of Decision by EPA – In 2008 - Settlement that gave MDEQ authority to remediate the Site and NRDP authority to add restoration elements • National Park Service also part of settlement because of Grant-Kohrs Ranch (Phases 15 and 16) – In 2013 – Phase 1 Construction • Combined remedy/restoration to maximize benefits with a cost-effective solution

Flood Hydrology of the Clark Fork River and its Tributaries Montana AWRA 2013 5

Remedial Action Objectives

• Remove or treat in place tailings and contaminated soils • Reconstruct a lower, hydraulically connected floodplain • Reconstruct unstable banks • Plant appropriate native vegetation in the floodplain • Include diverse habitats such as riparian and emergent wetlands

Flood Hydrology of the Clark Fork River and its Tributaries Montana AWRA 2013 6

Location of Reach A

Flood Hydrology of the Clark Fork River and its Tributaries Montana AWRA 2013 7

Hydrologic Setting

Start of Reach A • ~0.8 river miles upstream of the confluence of Lower Silver Bow Creek and Warms Springs Creek (Upper Clark Fork River) Reach A • Mainly grazing and hay production • Valley elevations 4,300 – 4,800 ft • Mountain elevations up to 10,000 ft (west) and 8,000 ft (east) • One larger urban area - Deer Lodge • 12 tributatires Tributaries • Lost Creek • Racetrack Creek • Cottonwood Creek • Little Blackfoot River End of Reach A • Garrison Junction Flood Hydrology of the Clark Fork River and its Tributaries Montana AWRA 2013 8

Warms Springs Ponds

2-Year Peak Flow (cfs) Station With WSP Without WSP Percent Increase Silver Bow Creek at Opportunity 304 304 0% Clark Fork near Galen 594 737 24% Clark Fork at Deer Lodge 848 1,165 37% Clark Fork at Gold Creek 2,374 2,374 0% 10-Year Peak Flow (cfs) Station With WSP Without WSP Percent Increase Silver Bow Creek at Opportunity 893 893 0% Clark Fork near Galen 1,250 2,009 61% Clark Fork at Deer Lodge 1,859 3,051 64% Clark Fork at Gold Creek 5,853 5,853 0% 100-Year Peak Flow (cfs) Station With WSP Without WSP Percent Increase Silver Bow Creek at Opportunity 2,367 2,367 0% Clark Fork near Galen 2,103 4,739 125% Clark Fork at Deer Lodge 3,414 6,779 99% Clark Fork at Gold Creek 11,840 11,840 0%

Regression Equation for the Western Region. This analysis was performed in May 2010.

9 Flood Hydrology of the Clark Fork River and its Tributaries Montana AWRA 2013 Mainstem Peak Hydrology

• Typical northern Rocky Mountain flow regime

Annual Hydrograph for CFR near Galen, MT (USGS Station 12323800)

Montana AWRA 2013 10 Flood Hydrology of the Clark Fork River and its Tributaries Mainstem Peak Hydrology

Regression Equations and Gage Record Analysis (CFR at Deer Lodge, MT)

West Regression Equation Southwest Regression Equation Percent Difference Percent Return Gage Records Peak Flow with Difference Interval PeakFQ (cfs) (cfs) PeakFQ Peak Flow (cfs) with PeakFQ 2-year 893 743 -17% 1,845 107% 5-year 1,490 4,642 212% 2,602 75% 10-year 1,925 5,937 208% 3,184 65% 25-year 2,510 7,320 192% 3,947 57% 50-year 2,966 8,536 188% 4,511 52% 100-year 3,436 9,763 184% 5,115 49% Analysis performed in 2013. • Regression equations appear to overpredict flows – Probably partly due to the storage effects of Warm Springs Ponds – Stations close to Missoula also seem to overpredict peak flows • PeakFQ (U.S.Geological Survey) of existing record was used for the more frequent events (up to the 25-year recurrence interval)

Montana AWRA 2013 11 Flood Hydrology of the Clark Fork River and its Tributaries Mainstem Peak Hydrology

Three active USGS stations in Reach A

USGS Station Years of Drainage Area Number Station Name Record (square miles) 12323800 Clark Fork near Galen, MT 24 561 12324200 Clark Fork at Deer Lodge, MT 34 916 Clark Fork above Little Blackfoot River near 12324400 Garrison, MT 4 1,140 • Relatively short period of records • Extended with similar drainages USGS Gages Investigated to Extend Clark Fork Gage Records

Years of Drainage Area USGS Station Number Station Name Record (square miles) 06033000 Boulder River near Boulder 381 12324590 Little Blackfoot River near Garrison 40 407 12331600 Clark Fork at Drummond 31 2,378 12332000 Middle Fork Rock Creek near Philipsburg 75 123 12340000 Blackfoot River near Bonner 73 2,290 12340500 Clark Fork above Missoula 78 5,999

Montana AWRA 2013 12 Flood Hydrology of the Clark Fork River and its Tributaries USGS Gages Investigated to Extend Clark Fork Gage Records

Correlation Extended Record Stations Correlated (R2) Used

Clark Fork near Galen with Middle Fork Rock Creek near Philipsburg 70% Yes

Clark Fork at Deer Lodge with Middle Fork Rock Creek near Phillipsburg 43% No

Clark Fork at Deer Lodge with Boulder River at Boulder 55% No

Clark Fork at Deer Lodge with Little Blackfoot River near Garrison 58% No

Clark Fork at Deer Lodge with Clark Fork at Drummond 67% No

Clark Fork at Deer Lodge with Clark Fork above Missoula minus Blackfoot River near Bonner 72% Yes

Clark Fork above Little Blackfoot River with Clark Fork at Deer Lodge 99.8% Yes

Montana AWRA 2013 13 Flood Hydrology of the Clark Fork River and its Tributaries Summary of Peak Flow Analysis Using Peak FQ

Clark Fork River at Deer Clark Fork River above Little Clark Fork near Galen Lodge Blackfoot River

Gage Record Extended Record Gage Record Extended Record Extended Record Extended Record Return Frequency (cfs) (cfs) (cfs) (cfs) (cfs) (cfs)

Years of Record 24 75 34 73 341 732

1.5-year(3) 441 - 679 - - -

2-year 584 827 893 1,090 923 1,249

5-year 961 1,177 1,490 1,604 1,571 2,218

10-year 1,216 1,380 1,925 1,929 2,047 2,842

25-year 1,535 1,608 2,510 2,319 2,687 3,568

50-year 1,767 1,757 2,966 2,594 3,186 4,056

100-year 1,993 1,893 3,436 2,857 3,700 4,497 1 Clark Fork above Little Blackfoot River record was extended using Clark Fork at Deer Lodge for 1979-2008. 2 Clark Fork above Little Blackfoot River record was extended using Clark Fork above Missoula minus Blackfoot River near Bonner for 1940-1978. 3 1.5-year event calculated only for existing gage record. Note: Blue shading indicates preferred values for this peak flow study.

Montana AWRA 2013 14 Flood Hydrology of the Clark Fork River and its Tributaries Estimated Peak Flows at USGS Gage Stations

Montana AWRA 2013 15 Flood Hydrology of the Clark Fork River and its Tributaries Major Tributary Peak Flow Analysis

USGS Station Years of Drainage Area Number Station Name Record (square miles)

12323840 Lost Creek near Anaconda, MT 8 26.4

12323850 Lost Creek near Galen, MT 10 60.5

12324100 Racetrack Creek below Granite Creek near 17 39.5 Anaconda, MT

12324250 Cottonwood Creek at Deer Lodge, MT 18 45.4

. Comparison of gage records to values calculated with the West and Southwest Regression Equations . Regression equation values for Cottonwood and Racetrack Creeks very low and for Lost Creek considerably higher

Montana AWRA 2013 16 Flood Hydrology of the Clark Fork River and its Tributaries Tributary Peak Flow Analysis

Montana AWRA 2013 17 Flood Hydrology of the Clark Fork River and its Tributaries Flow Duration

Flow duration is the measure of the length of time various flows occur on a river averaged over an extended period of time. • Calculating sediment transport • Understanding of the relative channel forming effects of floods of different frequencies Flow-duration curve for USGS gage CFR at Deer Lodge (1978-2012)

Based on this analysis – 2-year recurrence flow is exceeded 2.1% 0.021*365 days = almost 8 days. Montana AWRA 2013 18 Flood Hydrology of the Clark Fork River and its Tributaries Flow Duration

• Problems interpreting the information: – Duration of records of high flows may not be continues and may consist of two or more periods. – Look at the individual storms of records to understand the duration of the actual high-flow event.

• Designers should take the duration of bank full and out of bank flows into consideration when developing channel and floodplain designs.

19 QUESTIONS?

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