Hydraulic_Analysis_0005.pdf

Western Federal Lands Highway Division

610 E. Fifth Street Vancouver, WA

98661-3801

GLACIER NATIONAL PARK

SCOUR EVALUATION

1430-025P FORD CREEK BRIDGE

To: Benn Oltmann, P.E., WFLHD Bridge/Structures Functional Manager From: Matthew Dillin, P.E., WFLHD Hydraulics Engineer Date: November 23, 2020 Project: Glacier National Park Scour Evaluation – GLAC 311336

Background

United States Department of the Interior is developing plans to repair thirteen (13) bridges within Glacier National Park (Park), Montana. The primary goal of the project is to maximize the service life of each bridge while minimizing cost impacts. To support the development of the repair plans, Federal Lands Highway Division (WFLHD) was contracted to evaluate scour for five (5) of the bridges, including 1430-025P Ford Creek Bridge. Final scour and potential scour countermeasure recommendations for the Ford Creek Bridge are presented.

Recommendations

Abutment Scour Countermeasures

The Ford Creek Bridge qualifies as a “narrow opening bridge” according to FHWA- HIF-19-007; a full-width countermeasure protection is recommended.

Extend the depth of wood lagging on the right abutment wingwall to decrease to the rate of embankment material loss through abutment.

Proper filter design is required to prevent loss of roadway embankment material through the extended wood lagging.

Protect toe extended wood lagging with riprap abutment protection.

Riprap abutment protection channel side-slopes 2(h):1(v).

Riprap abutment protection to extend upstream and downstream 15-feet from the crossing.

Riprap abutment protection to extend back 10-feet from the abutment face.

Left abutment: Riprap Class 5 (FHWA FP-14), method B, 4-feet thick, crest 3,726.0-feet, bottom 3,709.5-feet, 0 feet wide toe.

Right abutment: Riprap Class 5 (FHWA FP-14), method B, 4-feet thick, crest 3,726.0-feet, bottom 3,709.5-feet, 0 feet wide toe.

200-year total scour elevations;

• Left Abutment: 3,701.8-feet

• Right Abutment: 3,701.8-feet

200-year pier scour at abutment elevation: 3,704.5-feet

Memo to: Benn Oltmann, WFLHD November 23, 2020

Operation and Maintenance

Countermeasures including placed riprap for controlling scour should be inspected annually and after each extreme flood event. Replace or reposition dislodged stone. Water deflected around trapped woody debris could potentially dislodge riprap stone. The presence of woody debris trapped upstream, beneath, and downstream of the bridge should be inspected annually and after each extreme flood event. Remove woody debris as needed for maintaining flow conveyance capacity and preventing logs deflecting flow towards the riprap or abutments.

Site Conditions

The existing structure is a 30-foot long by 16.1-foot wide prestressed concrete slab bridge (Photo 1). The existing bridge is approximately 600-feet upstream of the Ford Creek confluence with the North Fork Flathead River (Fig. 1). The bridge abutments are supported by pile bents, the depth of the piles are unkown. The stream is aligned approximately perpendicular to the road (Photos 2 and 4). Clearance under the bridge from the low-chord to the channel thalweg is approximately 11-feet (Photo 4). Channel bed appears fairly stable through the crossing; however, scour along the right abutment has begun to undermine the abutment wingwall and the bridge is losing roadway embankment material (Photo 7).

Ford Creek reach encompassing the bridge crossing is relatively stable. Plan form and channel characteristics are strongly influenced by the steep valley slope and coarse bed material. Upstream and downstream bottom widths were measured at approximately 16-feet (Photo 2). Channel bankfull depth is approximately 2-feet upstream and downstream of the crossing (Photos 2 and 3). Channel gradient is approximately 2.8-percent. Riffle-pool and step-pools are the dominant bedforms. Riffle crests and boulder weir crests control the stream profile. Streambed material gradation was measured using digital imaging tool in Hydraulic Toolbox (Version 4.2) with D100 28-inches, D85 12.2-inches, D50 6.7-inches (Photos 10 and 11). The banks are generally stable and well vegetated; however, some areas of local instability were observed directly downstream of the bridge. The bank toes tend to quickly armor, limiting the erosion extent.

Based on potential flood depths and available wood upstream of the channel, the stream can likely carry a large amount of small to moderate sized woody debris. Fairly large wood deposit was observed roughly 150-feet downstream of the crossing (Photo 8). Floodplain is well vegetated with grass, shrubs, and other wetland plants (Photos 4, 5, and 9).

Hydrology

No USGS gage station data is available for the stream. Peak discharges were estimated using USGS regression equations from Methods for estimating peak-flow frequencies at ungagged sites in Montana based on data through water year 2011 (USGS Scientific Investigations Report 2015-5019-F, 30 p.).

USGS StreamStats (version 4.4.0) web-based application was used for delineating the watershed and calculating drainage area 11.9 sq. miles (Fig. 2). Mean annual precipitation for the project area is 42.78-inches. The watershed is within NW Region Basin C (10.8 sq. miles, 2015-5019-F) and W Region Basin C (1.1 sq. miles, 2015-5019-F). The watershed is covered with 98.6-percent forest. Clear-cut logging was not observed in the basin. No major lakes or diversions occur in the basin. The drainage areas are generally steep and mountainous with moderately confined drainages. Elevations range from 3,714 to 9,038-feet (NAD83/WGS84). Low stream flow periods occur in January, February, and March. Higher flows occur with heavy rain, rain-on-snow, and snow melt in May, June, and July. Peak discharges estimates are presented in Table 1.

Water Surface Elevations and Flow Velocities

Surface-water Modeling System (Aquaveo, SMS 13.0.3) was used to develop and run SRH-2D, a two-dimensional, unsteady flow hydraulic model. The two-dimensional model was used for estimating the existing bridge water surface elevations, flow depths, and flow velocities. Terrain for the hydraulic model was created from existing ground topography obtained by WFL survey group in the fall of 2020.

Elevations based on NAVD88 GEOID 18 and provided in Montana State Plane Coordinate System NAD 83 2011. The model uses a gridded mesh with 0.6-foot sides under the bridge and an equilateral triangle mesh with roughly 2-foot sides in the main channel and adjacent floodplain. The bridge crossing is modeled as a free surface. The two-dimensional model extends 115-feet upstream and105-feet downstream (Fig. 7). Normal flow depth was set for the downstream boundary condition. The upstream boundary condition uses a hydrograph that includes the 2, 5, 10, 25, 50, 100, 200, and 500-year flood flows. Each flow was allowed to run until an equilibrium state was reached. The total simulation run time was set at 4-hours using a 0.15-second computation interval. Manning’s Roughness Coefficients of 0.035, 0.06, and 0.02 were selected for the main channel, floodplain, and roadway areas, respectively. The model was calibrated with apparent bankfull. Flow depths, water surface elevations, and design flow velocities are summarized in Table 1 and Figures 4, 5, and 6.

Scour

A HEC-18 (5th ED., April 2013) scour analysis was completed using the SRH-2D two-dimensional hydraulic model results (attached). The analysis includes contraction and abutment scour for the 50-year, 100-year, 200-year, and 500-year flood events. The analysis also includes pier scour at the abutment columns for the same events, to represent a situation where the roadway approach is washed out and the stream is flowing around the abutment columns. Channel profile is controlled by the steep slopes and coarse bed material and appears stable. A trend in long-term channel degradation was captured in Bridge Inspection Report cross-sectional surveys. Over the past 15-years, the channel has degraded approximately 1.3-feet on the upstream section and 1.6-feet on the downstream section. Expecting a similar trend in degradation over the next 50-years, a long-term degradation of 5-feet was assumed. Streambed material gradations were developed from visual observation of gravel bar and floodplain surfaces immediately upstream of the bridge.

Calculations assume 16-foot waterway width, vertical abutments, and flow impingement angles based on the two-dimensional modeling. Predicted scour is summarized in Table 1.

Riprap Sizing

Riprap design for the bridge abutments is based on Hydraulic Engineering Circular No. 23 (FHWA-NHI- 09-112) using equations 14.1 and 14.2. Calculations were performed using the local depth and velocity at the bridge abutment for the 50-year flood event. Specific gravity of the stone was assumed to be 2.65.

Slope of finished riprap surface is 2(h):1(v). For the left abutment, Class 1 riprap was calculated as the adequate design riprap size. For the right abutment, Class 5 riprap was calculated as the adequate design riprap size. Class 5 (FHWA, FP-14) riprap, minimum 4-feet thickness was selected for both abutments.

Stream Impacts

A moderate amount of turbidity and sediment is expected to be released when stream diversions are removed. The amount of turbidity and sediment will be reduced by removing the flow diversions gradually introducing the stream flow over an extended two to three-hour time.

Floodplain and Flood-rise Limitations

The site is not mapped by the Federal Emergency Management Agency (FEMA) as being in a special flood hazard area. A detailed FEMA mapping study has not been completed for the site. No base flood elevations have been determined. The proposed scour countermeasures are not expected to impact flooding of private property or insurable structures.

Attachments: Table 1 – Scour Summary Figure 1 – Site Location Figure 2 – Drainage Area Figure 3 – Water Surface Profile Figure 4 – Flow Velocity Figure 5 – Flow Depth Figure 6 – Water Surface Elevations Figure 7 – SRH2D Model Mesh Figure 8 – 100-year Scour Figure 9 – 200-year Scour Figure 10 – 500 year Scour Photographs 1 to 11 Peak Discharge Estimates

Cc: Sven Leon, WFLHD Hydraulics Functional Manager

To: By: Matthew Dillin, P.E.

Project: Glacier National Park Scour Evaluation - GLAC 311336 WFLHD Hydraulics Engineer

Bridge: Date:

BRIDGE STRUCTURE SUMMARY

Low Chord Elevation 3725.0 feet (Project Datum) Minimum Design Freeboard NA feet above the 100-year flood * Needed for woody debris passage.

Stream Bottom Elevation 3713.7 feet Clearance to Stream Bot. 11.3 feet Waterway Width 16 feet 30 feet (vertical at 100-yr WS) Skew 0 degrees relative to stream Bridge Length (feet) 30 Bridge/Stream CL Sta Bridge Start Bridge End Abutment Type Vertical abutments

HYDRAULIC & HYDROLOGIC SUMMARY Hydraulic Model: HECRAS 5.0 Flood Frequency Yr 2 25 50 100 200 500 Exceedance Probability % 50 4 2 1 0.5 0.2 Discharge cfs 557 2230 3230 4640 6680 10800 Modeled Water Surface Elevation Elev 3715.8 3718.3 3719.3 3720.9 3722.4 3724.2 Elevation Datum Conversion Ft 0.0 0.0 0.0 0.0 0.0 0.0 Project Water Surface Elevation Elev 3715.8 3718.3 3719.3 3720.9 3722.4 3724.2 Clearance above WS Ft 9.2 6.7 5.7 4.1 2.6 0.8 Existing Water Surface Elevation Elev NA NA NA NA NA NA Predicted Flood Rise Ft NA NA NA NA NA NA Design Flow Velocity Ft/sec 7.7 13.2 14.7 15.1 15.8 19.1 Scour Base Elevation (Channel Thalweg) Elev 3713.7 3713.7 3713.7 3713.7 Contraction Scour Depth Ft 0.6 1.2 1.1 0.6 Stream Degradation Depth Ft 5.0 5.0 5.0 5.0 Vertical Contraction Scour Depth Ft 0.0 0.0 0.0 0.0 Left Abutment Scour Depth Ft 2.5 3.3 6.9 9.1 Right Abutment Scour Depth Ft 2.5 3.3 6.9 9.1 Total Left Abutment Scour Elevation ** Elev 3706.2 3705.4 3701.8 3699.6 Total Right Abutment Scour Elevation ** Elev 3706.2 3705.4 3701.8 3699.6 Pier 1 Scour Depth Ft 2.3 2.7 3.1 3.2 Pier 2 Scour Depth Ft Total Pier 1 Scour Elevation ** Elev* 3705.8 3704.8 3704.5 3704.9 Total Pier 2 Scour Elevation ** Elev*

* or to bedrock when present.

** includes CS+LTD or VCS for SCF

Streambed material grain size (inches) D100/D85/D50 28 12.2 6.5 Scour Design Basis Project Elevation Datum

BRIDGE HYDRAULICS & SCOUR ANALYSIS SUMMARY

Benn Oltmann, WFLHD Bridge/Structures Functional Manager

11/23/20201430-025P Ford Creek Bridge

Project

HEC-18

FordCreek_Bridge-Hydraulics-Scour_Summary.xls

Bridge Location

Project Site Location

Image from Google Earth Pro, image date 7/24/2017

N

FIGURE 1

FORD CREEK BRIDGE

PROJECT LOCATION

0 250 feet

Image from Google Earth Pro, image date 7/24/2017.

FIGURE 2

FORD CREEK BRIDGE

DRAINAGE AREA

Ford Creek Bridge

11.1 sq. miles

N

0 1.5 mile

FIGURE 3

FORD CREEK BRIDGE

WATER SURFACE PROFILE

SRH2D - Two-Dimensional hydraulic model.

Design Value Location

FIGURE 4

FORD CREEK BRIDGE

100-YEAR FLOW VELOCITY

2-yr

500-yr

100-yr50-yr

25-yr

10-yr

200-yr

5-yr

HECRAS 5.0 - Two-Dimensional hydraulic model.

Design Value Location

FIGURE 5

FORD CREEK BRIDGE

100-YEAR FLOW DEPTH

2-yr

500-yr

100-yr

50-yr

25-yr

10-yr

Design Value Location

FIGURE 6

FORD CREEK BRIDGE

100-YEAR WATER SURFACE

2-yr

500-yr

100-yr

50-yr

25-yr

10-yr

US Hydro Boundary

Mesh

FIGURE 7

FORD CREEK BRIDGE

SRH2D MODEL

DS Normal Depth Boundary

Bridge Mesh

FIGURE 8

100-YEAR SCOUR ANALYSIS

FIGURE 9

200-YEAR SCOUR ANALYSIS

FIGURE 10

500-YEAR SCOUR ANALYSIS

Photos - Ford Creek Ford Creek Bridge

PHOTO 1

PHOTO 2

PHOTO 3

9/30/2020

Channel aligned approximately perpendicular to roadway. Straight river reach approaching bridge. Step-pools bed forms visible upstream of bridge.

Looking downstream from bridge deck.

Ford Creek Bridge approach looking SW.

Looking upstream from bridge deck.

Channel aligned approximately perpendicular to roadway. Coarse bed material visible along toe of banks.

PHOTO 4

PHOTO 5

PHOTO 6

9/30/2020

Left abutment setup on small bankfull bench and out of main channel. No signs of abutment scour or long term degradation.

Looking upstream at left abutment.

Bridge inlet looking downstream.

Bridge located on a fairly straight reach.

Approach roughly perpendicular to the bridge inlet. Channel is relatively steep.

Banks are well vegetated with coarse bed material along bank toe.

Bridge outlet looking upstream.

Bankfull with approximately 18-feet.

Areas of local instability. Coarse bed material with visible step-pool bed form.

PHOTO 7

PHOTO 8

PHOTO 9

9/30/2020

Active channel width approximately 18-feet. Banks stable and well vegetated.

Step-pool dominant bed form. Boulder, cobble, and gravel streambed material.

Looking at right abutment.

Channel upstream of bridge.

Scour along the toe of existing wing wall.

Embankment material starting to pipe out from under existing wing wall.

Looking downstream, roughly 150-feet downstream from bridge.

Large woody debris deposit within main channel.

PHOTO 10

PHOTO 11

9/30/2020

Streambed material on exposed bar.

Streambed material on exposed bar.

1430-025P Ford Creek Bridge - StreamStats Report

Basin Characteristics

Parameter Code Parameter Description Value Unit

CONTDA Area that contributes flow to a point on a stream 11.9 square miles

PRECIP Mean Annual Precipitation 42.78 inches

FOREST Percentage of area covered by forest 98.6 percent

SLOP50_30M Percent area with slopes greater than 50 percent from 30-meter DEM. 4.6 percent

BSLDEM30M Mean basin slope computed from 30 m DEM 20.9 percent

ELEV Mean Basin Elevation 4987.7 feet

ELEVMAX Maximum basin elevation feet

Peak-Flow Statistics Parameters[91 Percent (10.8 square miles) NW Region BasinC 2015 5019F]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 2.43 1560

Peak-Flow Statistics Parameters[9 Percent (1.09 square miles) W Region BasinC 2015 5019F]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 0.6 2470

PRECIP Mean Annual Precipitation 42.78 inches 14.6 62.1

FOREST Percent Forest 98.6 percent 20.4 99.1

Peak-Flow Statistics Flow Report[91 Percent (10.8 square miles) NW Region BasinC 2015 5019F]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu SEp

1.5 Year Peak Flood 142 ft^3/s 29.2 691 115

2 Year Peak Flood 182 ft^3/s 49.2 674 88.9

2 33 Year Peak Flood 203 ft^3/s 60.5 681 80.4

5 Year Peak Flood 342 ft^3/s 146 802 52.8

Region ID: MT Workspace ID: MT20201030161743923000 Clicked Point (Latitude, Longitude): 48.87368, -114.35976 Time: 2020-10-30 09:18:02 -0700

Page 2 of 8StreamStats

10/30/2020https://streamstats.usgs.gov/ss/

Statistic Value Unit PIl PIu SEp

10 Year Peak Flood 516 ft^3/s 288 924 34.4

25 Year Peak Flood 891 ft^3/s 729 1090 9.1

50 Year Peak Flood 1370 ft^3/s 1070 1760 11.3

100 Year Peak Flood 2070 ft^3/s 1540 2790 13.6

200 Year Peak Flood 3140 ft^3/s 2210 4450 16

500 Year Peak Flood 5360 ft^3/s 3520 8160 19.3

Peak-Flow Statistics Flow Report[9 Percent (1.09 square miles) W Region BasinC 2015 5019F]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu SEp

1.5 Year Peak Flood 97.3 ft^3/s 39.4 240 59.4

2 Year Peak Flood 118 ft^3/s 49.4 282 56.5

2 33 Year Peak Flood 128 ft^3/s 54.1 303 55.7

5 Year Peak Flood 174 ft^3/s 76 398 53.4

10 Year Peak Flood 222 ft^3/s 97.7 504 52.8

25 Year Peak Flood 270 ft^3/s 119 615 53.2

50 Year Peak Flood 311 ft^3/s 134 722 54.2

100 Year Peak Flood 352 ft^3/s 149 834 56

200 Year Peak Flood 393 ft^3/s 161 956 58

500 Year Peak Flood 440 ft^3/s 173 1120 61.4

Peak-Flow Statistics Flow Report[Area-Averaged]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu

1.5 Year Peak Flood 138 ft^3/s 30.1 650

2 Year Peak Flood 176 ft^3/s 49.2 638

2 33 Year Peak Flood 196 ft^3/s 59.9 647

5 Year Peak Flood 327 ft^3/s 140 765

10 Year Peak Flood 489 ft^3/s 271 886

25 Year Peak Flood 834 ft^3/s 673 1050

50 Year Peak Flood 1270 ft^3/s 985 1670

100 Year Peak Flood 1910 ft^3/s 1410 2610

200 Year Peak Flood 2890 ft^3/s 2020 4130

500 Year Peak Flood 4910 ft^3/s 3220 7520

Peak-Flow Statistics Citations

Sando, Roy, Sando, S.K., McCarthy, P.M., and Dutton, D.M.,2016, Methods for estimating peak-flow frequencies at ungaged sites in Montana based on data through water year 2011: U.S. Geological Survey Scientific Investigations Report 2015–5019–F, 30 p.

(https://doi.org/10.3133/sir20155019)

Low-Flow Statistics Parameters[9 Percent (1.09 square miles) W Region LowFlow GLS 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 6.4 2520

SLOP50_30M Slopes_gt_50pct_from_30m_DEM 4.6 percent 1.87 67.5

Low-Flow Statistics Parameters[91 Percent (10.8 square miles) NW Region LowFlow GLS 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 7.74 1560

SLOP50_30M Slopes_gt_50pct_from_30m_DEM 4.6 percent 0.06 66

Page 3 of 8StreamStats

Low-Flow Statistics Flow Report[9 Percent (1.09 square miles) W Region LowFlow GLS 2015 5019G]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu SEp

7 Day 10 Year Low Flow 0.732 ft^3/s 0.238 2.25 68.5

Low-Flow Statistics Flow Report[91 Percent (10.8 square miles) NW Region LowFlow GLS 2015 5019G]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu SEp

7 Day 10 Year Low Flow 0.108 ft^3/s 0.0187 0.623 78.1

Low-Flow Statistics Flow Report[Area-Averaged]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu

7 Day 10 Year Low Flow 0.165 ft^3/s 0.0387 0.771

Low-Flow Statistics Citations

McCarthy, P.M., Sando, Roy, Sando, S.K., and Dutton, D.M.,2016, Methods for estimating streamflow characteristics at ungaged sites in western Montana based on data through water year 2009: U.S. Geological Survey Scientific Investigations Report 2015–5019–G, 19 p.

(https://doi.org/10.3133/sir20155019)

Flow-Duration Statistics Parameters[9 Percent (1.09 square miles) W Region Annual MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 6.4 2520

SLOP50_30M Slopes_gt_50pct_from_30m_DEM 4.6 percent 1.87 67.5

Flow-Duration Statistics Parameters[91 Percent (10.8 square miles) NW Region Annual MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 7.74 1560

PRECIP Mean Annual Precipitation 42.78 inches 20.7 83.2

Flow-Duration Statistics Flow Report[9 Percent (1.09 square miles) W Region Annual MeanDur 2015 5019G]

Statistic Value Unit

20 Percent Duration 5.96 ft^3/s

80 Percent Duration 1.43 ft^3/s

Flow-Duration Statistics Flow Report[91 Percent (10.8 square miles) NW Region Annual MeanDur 2015 5019G]

Statistic Value Unit

20 Percent Duration 30.6 ft^3/s

80 Percent Duration 5.1 ft^3/s

Flow-Duration Statistics Flow Report[Area-Averaged]

Statistic Value Unit

20 Percent Duration 28.4 ft^3/s

80 Percent Duration 4.77 ft^3/s

Flow-Duration Statistics Citations

McCarthy, P.M., Sando, Roy, Sando, S.K., and Dutton, D.M.,2016, Methods for estimating streamflow characteristics at ungaged sites in western Montana based on data through water year 2009: U.S. Geological Survey Scientific Investigations Report 2015–5019–G, 19 p.

(https://doi.org/10.3133/sir20155019)

Annual Flow Statistics Parameters[9 Percent (1.09 square miles) W Region Annual MeanDur 2015 5019G]

Page 4 of 8StreamStats

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 6.4 2520

SLOP50_30M Slopes_gt_50pct_from_30m_DEM 4.6 percent 1.87 67.5

Annual Flow Statistics Parameters[91 Percent (10.8 square miles) NW Region Annual MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 7.74 1560

PRECIP Mean Annual Precipitation 42.78 inches 20.7 83.2

Annual Flow Statistics Flow Report[9 Percent (1.09 square miles) W Region Annual MeanDur 2015 5019G]

Statistic Value Unit

Median Annual Flow 2.94 ft^3/s

Mean Annual Flow 4.65 ft^3/s

Annual Flow Statistics Flow Report[91 Percent (10.8 square miles) NW Region Annual MeanDur 2015 5019G]

Statistic Value Unit

Median Annual Flow 12.1 ft^3/s

Mean Annual Flow 20.6 ft^3/s

Annual Flow Statistics Flow Report[Area-Averaged]

Statistic Value Unit

Median Annual Flow 11.3 ft^3/s

Mean Annual Flow 19.1 ft^3/s

Annual Flow Statistics Citations

McCarthy, P.M., Sando, Roy, Sando, S.K., and Dutton, D.M.,2016, Methods for estimating streamflow characteristics at ungaged sites in western Montana based on data through water year 2009: U.S. Geological Survey Scientific Investigations Report 2015–5019–G, 19 p.

(https://doi.org/10.3133/sir20155019)

Monthly Flow Statistics Parameters[91 Percent (10.8 square miles) NW Region Season3 MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 7.74 1560

PRECIP Mean Annual Precipitation 42.78 inches 20.7 83.2

Monthly Flow Statistics Parameters[91 Percent (10.8 square miles) NW Region Season1 MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 7.74 1560

PRECIP Mean Annual Precipitation 42.78 inches 20.7 83.2

Monthly Flow Statistics Parameters[91 Percent (10.8 square miles) NW Region Season2 MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 7.74 1560

PRECIP Mean Annual Precipitation 42.78 inches 20.7 83.2

Monthly Flow Statistics Parameters[9 Percent (1.09 square miles) W Region Season3 MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 6.4 2520

SLOP50_30M Slopes_gt_50pct_from_30m_DEM 4.6 percent 1.87 67.5

Monthly Flow Statistics Parameters[9 Percent (1.09 square miles) W Region Season1 MeanDur 2015 5019G]

Page 5 of 8StreamStats

CONTDA Contributing Drainage Area 11.9 square miles 6.4 2520

SLOP50_30M Slopes_gt_50pct_from_30m_DEM 4.6 percent 1.87 67.5

Monthly Flow Statistics Parameters[9 Percent (1.09 square miles) W Region Season2 MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 6.4 2520

SLOP50_30M Slopes_gt_50pct_from_30m_DEM 4.6 percent 1.87 67.5

Monthly Flow Statistics Flow Report[91 Percent (10.8 square miles) NW Region Season3 MeanDur 2015 5019G]

Statistic Value Unit

November Mean Flow 8.65 ft^3/s

December Mean Flow 6.7 ft^3/s

January Mean Flow 5.12 ft^3/s

February Mean Flow 5.67 ft^3/s

Monthly Flow Statistics Flow Report[91 Percent (10.8 square miles) NW Region Season1 MeanDur 2015 5019G]

Statistic Value Unit

March Mean Flow 6.01 ft^3/s

April Mean Flow 14.6 ft^3/s

May Mean Flow 39.4 ft^3/s

June Mean Flow 47.8 ft^3/s

Monthly Flow Statistics Flow Report[91 Percent (10.8 square miles) NW Region Season2 MeanDur 2015 5019G]

Statistic Value Unit

July Mean Flow 20.2 ft^3/s

August Mean Flow 8.92 ft^3/s

September Mean Flow 7.25 ft^3/s

October Mean Flow 10.1 ft^3/s

Monthly Flow Statistics Flow Report[9 Percent (1.09 square miles) W Region Season3 MeanDur 2015 5019G]

Statistic Value Unit

November Mean Flow 1.93 ft^3/s

December Mean Flow 1.76 ft^3/s

January Mean Flow 1.7 ft^3/s

February Mean Flow 1.76 ft^3/s

Monthly Flow Statistics Flow Report[9 Percent (1.09 square miles) W Region Season1 MeanDur 2015 5019G]

Statistic Value Unit

March Mean Flow 2.76 ft^3/s

April Mean Flow 6.44 ft^3/s

May Mean Flow 12.4 ft^3/s

June Mean Flow 10.3 ft^3/s

Monthly Flow Statistics Flow Report[9 Percent (1.09 square miles) W Region Season2 MeanDur 2015 5019G]

Statistic Value Unit

July Mean Flow 4.51 ft^3/s

August Mean Flow 2.57 ft^3/s

September Mean Flow 1.91 ft^3/s

October Mean Flow 1.85 ft^3/s

Page 6 of 8StreamStats

Monthly Flow Statistics Flow Report[Area-Averaged]

Statistic Value Unit

November Mean Flow 8.04 ft^3/s

December Mean Flow 6.25 ft^3/s

January Mean Flow 4.81 ft^3/s

February Mean Flow 5.31 ft^3/s

March Mean Flow 5.71 ft^3/s

April Mean Flow 13.9 ft^3/s

May Mean Flow 36.9 ft^3/s

June Mean Flow 44.4 ft^3/s

July Mean Flow 18.8 ft^3/s

August Mean Flow 8.34 ft^3/s

September Mean Flow 6.76 ft^3/s

October Mean Flow 9.35 ft^3/s

Monthly Flow Statistics Citations

McCarthy, P.M., Sando, Roy, Sando, S.K., and Dutton, D.M.,2016, Methods for estimating streamflow characteristics at ungaged sites in western Montana based on data through water year 2009: U.S. Geological Survey Scientific Investigations Report 2015–5019–G, 19 p.

(https://doi.org/10.3133/sir20155019)

Seasonal Flow Statistics Parameters[9 Percent (1.09 square miles) W Region LowFlow GLS 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 6.4 2520

SLOP50_30M Slopes_gt_50pct_from_30m_DEM 4.6 percent 1.87 67.5

Seasonal Flow Statistics Parameters[91 Percent (10.8 square miles) NW Region LowFlow GLS 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 11.9 square miles 7.74 1560

PRECIP Mean Annual Precipitation 42.78 inches 20.7 83.2

Seasonal Flow Statistics Flow Report[9 Percent (1.09 square miles) W Region LowFlow GLS 2015 5019G]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu SEp

Jul_to_Oct_14_Day_5_Yr_Low_Flow 1.29 ft^3/s 0.411 4.05 71.5

Seasonal Flow Statistics Flow Report[91 Percent (10.8 square miles) NW Region LowFlow GLS 2015 5019G]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu SEp

Jul_to_Oct_14_Day_5_Yr_Low_Flow 2.53 ft^3/s 0.609 10.5 93.2

Seasonal Flow Statistics Flow Report[Area-Averaged]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu

Jul_to_Oct_14_Day_5_Yr_Low_Flow 2.42 ft^3/s 0.591 9.91

Seasonal Flow Statistics Citations

McCarthy, P.M., Sando, Roy, Sando, S.K., and Dutton, D.M.,2016, Methods for estimating streamflow characteristics at ungaged sites in western Montana based on data through water year 2009: U.S. Geological Survey Scientific Investigations Report 2015–5019–G, 19 p.

(https://doi.org/10.3133/sir20155019)

Page 7 of 8StreamStats

USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty.

USGS Software Disclaimer: This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use.

USGS Product Names Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Application Version: 4.4.0

Page 8 of 8StreamStats

Vancouver, WA

98661-3801

GLACIER NATIONAL PARK

1430-007P FISH CREEK BRIDGE

Glacier National Park (Park), Montana. The primary goal of the project is to maximize the service life of each bridge while minimizing cost impacts. To support the development of the repair plans, Federal Lands Highway Division (WFLHD) was contracted to evaluate scour for five (5) of the bridges, including 1430-007P Fish Creek Bridge. Final scour and potential scour countermeasure recommendations for the Fish Creek Bridge are presented.

Recommendations

Abutment Scour Countermeasures

The Fish Creek Bridge qualifies as a “narrow opening bridge” according to FHWA- HIF-19-007; a full-width countermeasure protection is recommended.

Abutment protection 2(h):1(v) channel side-slopes.

Abutment protection to extend upstream and downstream 20-feet from the crossing.

Abutment protection to extend back, 10-feet from the abutment face.

Riprap Class 2 (FHWA FP-14), method B, 2-feet thick, crest 3,207.0-feet, bottom 3,194.0-feet, 0 feet wide toe.

200-year total abutment scour elevations;

• Left Abutment: 3,189.7-feet

• Right Abutment: 3,189.7-feet

200-year pier scour elevation at abutments: 3,192.0-feet

Pier Scour Countermeasures

The Fish Creek Bridge qualifies as a “narrow opening bridge” according to FHWA- HIF-19-007; a full-width countermeasure protection is recommended.

Riprap Class 6 (FHWA FP-14), method B, 6-feet thick, crest 3,195.0 feet, extending 7-feet from pier (all around).

200-year total scour elevations;

• Pier 1: 3,189.4-feet

• Pier 2: 3,189.2-feet each extreme flood event. Replace or reposition dislodged stone. Water deflected around trapped woody debris could potentially dislodge riprap stone. The presence of woody debris trapped upstream, beneath, and downstream of the bridge should be inspected annually and after each extreme flood event. Remove woody debris as needed for maintaining flow conveyance capacity and preventing logs deflecting flow towards the riprap or abutments.

Site Conditions

The existing structure is a 62.8-foot long by 29.8-foot wide timber beam bridge, with two piers and a maximum span length of 23-feet. As-builts show that the existing piers are on spread footings with a bottom elevation of roughly 3,193.5-feet. The abutments are supported by five pedestals with bottom elevations of 3,197.5-feet (4-feet tall) and 3,200.5-feet (6.4-feet tall) for the left and right abutments, respectively. The existing bridge is approximately 1,700-feet upstream of the Fish Creek confluence with Lake McDonald (Fig. 1). The stream is aligned approximately 35-degrees to the road (Photos 2 and 4).

Clearance under the bridge from the low-chord to the channel thalweg is approximately 10-feet (Photos 4 and 5). A moderate scour hole is observed at the outlet and along the south pier (Photos 5 and 6). Erosion was observed along the north and south abutments (Photos 7 & 8).

Fish Creek is relatively stable. Plan form and channel characteristics are strongly influenced by the steep valley slope and coarse bed material. Both upstream and downstream the active channel width was measured at approximately 22 to 26-feet (Photos 9 & 10). Active channel depth is approximately 2-feet.

Flood-prone width is 40 to 50-feet. Flood-prone depth is 3 to 4-feet. Channel gradient is approximately 2-percent in the riffles and up to 5-percent in the cascades. Pool-riffle and cascade are the dominant bed forms. Cobble-boulder sills control the stream profile. Streambed material gradation measured using digital imaging tool in Hydraulic Toolbox (Version 4.2) with D100 23-inches, D85 13-inches, D50 6.7-inches (Photos 11 & 12). The banks are moderately stable where vegetated. Bank erosion occurs where sediment and woody debris in the channel deflect stream flow towards an erodible bank. The bank toes tend to quickly armor, limiting the erosion extent.

Based on potential flood depths and available wood, the stream can likely carry a large amount of small to moderate sized woody debris. Floodplain is thickly vegetated with grass, shrubs, and other wetland plants (Photos 9 & 10).

Hydrology

No USGS gage station data is available for the stream. Peak discharges were estimated using USGS regression equations from Methods for estimating peak-flow frequencies at ungagged sites in Montana based on data through water year 2011 (USGS Scientific Investigations Report 2015-5019-F, 30 p.).

USGS StreamStats (version 4.4.0) web-based application was used for delineating the watershed and calculating drainage area 14.2 sq. miles (Fig. 2). Mean annual precipitation for the project area is 37.4-inches. The watershed is entirely within NW Region Basin C (2015-5019-F) and covered with 94-percent forest. Clear-cut logging was not observed in the basin. No major flow diversions or lakes occur. The drainage areas are steeply mountainous with moderately confined drainages. Elevations range from 3,200 to 6,630-feet (NAD83/WGS84). Low stream flow periods occur in January, February, and March. Higher flows occur with heavy rain, rain-on-snow, and snow melt in May, June, and July. Peak discharges estimates are presented in Table 1.

Water Surface Elevations and Flow Velocities

Surface-water Modeling System (Aquaveo, SMS 13.0.3) was used to develop and run SRH-2D, a two-dimensional, unsteady flow hydraulic model. The two-dimensional model was used for estimating the existing bridge water surface elevations, flow depths, and flow velocities. Terrain for the hydraulic model was created from existing ground topography obtained by WFL survey group in the fall of 2020.

Elevations based on NAVD88 GEOID 18 and provided in Montana State Plane Coordinate System NAD 83 2011. The model uses a gridded mesh with 1.6-foot sides under the bridge and an equilateral triangle mesh with roughly 5-foot sides in the main channel and overbanks. The crossing is modeled as pressure flow with a low-chord elevation of 3,205-feet and a crest elevation of 3207.5-feet. The model extends 300-feet upstream and 330-feet downstream (Fig. 7). Normal flow depth was set for the downstream boundary condition. The upstream boundary condition uses a hydrograph that includes the 2, 5, 10, 25, 50, 100, 200, and 500-year flood flows. Each flow was allowed to run until an equilibrium state was reached. The total simulation run time was set at 4-hours using a 0.15-second computation interval.

Manning’s Roughness Coefficients of 0.035, 0.06, and 0.02 were selected for the main channel, floodplain, and roadway areas, respectively. The model was calibrated with apparent bankfull. Flow depths, water surface elevations, and design flow velocities are summarized in Table 1 and Figures 4, 5, and 6.

Scour

A HEC-18 (5th ED., April 2013) scour analysis was completed using the SRH-2D two-dimensional hydraulic model results (attached). The analysis includes contraction, abutment, and coarse bed pier scour for the 100-year, 200-year, and 500-year flood events. The analysis also includes pier scour at the abutment columns for the same events, to represent a situation where the roadway approach is washed out and the stream is flowing around the abutment columns. Vertical contraction scour for the 500-year flood event was also evaluated. Channel profile is controlled by the coarse cobble-boulder bed material and appears stable.

Long-term channel degradation was assumed zero. Streambed material gradations were developed from visual observation of gravel bar and floodplain surfaces immediately upstream of the bridge. Calculations assume 26.6-foot waterway width, spill-through abutments, and flow impingement angles based on the two-dimensional modeling. Predicted scour is summarized in Table 1.

Riprap Sizing

Riprap design for the bridge abutments is based on Hydraulic Engineering Circular No. 23 (FHWA-NHI- 09-112) using equations 14.1 and 14.2. Calculations were performed using the local depth and velocity at the bridge abutment for 200-year flood event. Specific gravity of the stone was assumed to be 2.65. Slope of finished riprap surface is 2(h):1(v). For the left and right abutments, Class 1 riprap was calculated as the adequate design riprap size. To account for unknown flow impingement angles caused by shifting debris and mid-channel sediment deposits, Class 2 (FHWA, FP-14) riprap, minimum 2-feet thickness was selected.

Riprap design for the bridge pier is based on Hydraulic Engineering Circular No. 23 (FHWA-NHI-09-

112) using equation 11.1. Calculations were performed using the pier local flow velocity for the 200-year flood event. Specific gravity of the stone was assumed to be 2.65. Class 6 (FHWA, FP-14) riprap, minimum 6-feet thickness was selected.

Stream Impacts

A moderate amount of turbidity and sediment is expected to be released when the stream diversions are removed. The amount of turbidity and sediment will be reduced by removing the stream diversions gradually introducing the stream flow over an extended two to three-hour time.

Floodplain and Flood-rise Limitations

The site is not mapped by the Federal Emergency Management Agency (FEMA) as being in a special flood hazard area. A detailed FEMA mapping study has not been completed for the site. No base flood

Figure 2 – Drainage Area Figure 3 – Water Surface Profile Figure 4 – Flow Velocity Figure 5 – Flow Depth Figure 6 – Water Surface Elevations Figure 7 – SRH2D Model Mesh Figure 8 – 100-year Scour Figure 9 – 500-year Scour Photographs 1 to 12

Bridge: Date:

BRIDGE STRUCTURE SUMMARY

Low Chord Elevation 3205.0 feet (Project Datum) Minimum Design Freeboard NA feet above the 100-year flood * Needed for woody debris passage.

Stream Bottom Elevation 3194.9 feet Clearance to Stream Bot. 10.1 feet Waterway Width 29 feet 57 feet (Spill-through at 100-yr WS) Skew 35 degrees relative to stream Bridge Length (feet) 76 Bridge/Stream CL Sta Bridge Start Bridge End Abutment Type Spill-though abutments

HYDRAULIC & HYDROLOGIC SUMMARY Hydraulic Model: HECRAS 5.0 Flood Frequency Yr 2 25 50 100 200 500 Exceedance Probability % 50 4 2 1 0.5 0.2 Discharge cfs 213 1020 1560 2350 3520 5970 Modeled Water Surface Elevation Elev 3199.5 3202.3 3203.5 3204.9 3206.8 3211.6 Elevation Datum Conversion Ft 0.0 0.0 0.0 0.0 0.0 0.0 Project Water Surface Elevation Elev 3199.5 3202.3 3203.5 3204.9 3206.8 3211.6 Clearance above WS Ft 5.5 2.7 1.5 0.1 -1.8 -6.6 Existing Water Surface Elevation Elev NA NA NA NA NA NA Predicted Flood Rise Ft NA NA NA NA NA NA Design Flow Velocity Ft/sec 7.6 11.5 11.5 11.5 11.1 10.1 Scour Base Elevation (Channel Thalweg) Elev 3194.9 3194.9 3194.9 3194.9 Contraction Scour Depth Ft 0.0 0.0 0.0 0.0 Stream Degradation Depth Ft 0.0 0.0 0.0 0.0 Vertical Contraction Scour Depth Ft 0.0 0.0 0.0 0.6 Left Abutment Scour Depth Ft 0.0 2.5 5.2 4.8 Right Abutment Scour Depth Ft 0.0 2.5 5.2 4.8 Total Left Abutment Scour Elevation ** Elev 3194.9 3192.4 3189.7 3190.1 Total Right Abutment Scour Elevation ** Elev 3194.9 3192.4 3189.7 3190.1 Pier Abutment Scour Depth Ft 2.6 2.8 2.9 2.9 Pier 1 Scour Depth Ft 4.9 4.9 5.5 6.1 Pier 2 Scour Depth Ft 5.6 5.9 5.7 6.4 Total Pier Abutment Scour Elevation ** Elev* 3192.3 3192.1 3192.0 3192.0 Total Pier 1 Scour Elevation ** Elev* 3190.0 3190.0 3189.4 3188.2 Total Pier 2 Scour Elevation ** Elev* 3189.3 3189.0 3189.2 3187.9

* or to bedrock when present.

** includes CS+LTD or VCS for SCF

Streambed material grain size (inches) D100/D85/D50 23 13 6.7 Scour Design Basis Project Elevation Datum

BRIDGE HYDRAULICS & SCOUR ANALYSIS SUMMARY

Benn Oltmann, WFLHD Bridge/Structures Functional Manager

11/23/20201430-007P Fish Creek Bridge

Project

FishCreek_Bridge-Hydraulics-Scour_Summary.xls

Image from Google Earth Pro, image date 7/26/2014

N

FIGURE 1

FISH CREEK BRIDGE

PROJECT LOCATION

Fish Creek Bridge

Campground

Image from Google Earth Pro, image date 7/26/2014.

FISH CREEK BRIDGE

DRAINAGE AREA

Fish Creek Bridge

14.2 sq. miles

0 2 miles

FISH CREEK BRIDGE

WATER SURFACE PROFILE

Design Value Location

FIGURE 4

FISH CREEK BRIDGE

100-YEAR FLOW VELOCITY

2-yr

500-yr

100-yr

50-yr

25-yr

10-yr

Design Value Location

FIGURE 5

FISH CREEK BRIDGE

100-YEAR FLOW DEPTH

2-yr

500-yr

100-yr

50-yr 25-yr

10-yr

Design Value Location

FIGURE 6

FISH CREEK BRIDGE

100-YEAR WATER SURFACE

2-yr

500-yr

100-yr

50-yr

25-yr

10-yr

US Hydro Boundary

Mesh

FIGURE 7

FISH CREEK BRIDGE

SRH2D MESH MODEL

DS Normal Depth Boundary

Bridge Mesh with Piers

Photos - Fish Creek Fish Creek Bridge

PHOTO 2

PHOTO 3

9/30/2020

Roughly 9-feet of clearance between channel thalweg and bridge low-chord.

Channel aligned approximately 35-degrees to roadway.

Looking downstream from bridge deck.

Fish Creek Bridge approach looking north.

Looking upstream from bridge deck.

Downstream channel roughly perpendicular to roadway.

PHOTO 5

PHOTO 6

9/30/2020

Small scour hole along the south pier and downstream of the pier. Bridge is located on a bend and the south pier is located on the outside of the bend.

Looking upstream at south pier.

Bridge inlet looking downstream.

Bridge located on a bend. Approach angle roughly 35-degrees coming into the bridge inlet. South (right) pier is located on the outside of bend and show signs of erosion along inside face. Front face of north (left) pier shows signs of abrasion damage.

Bridge outlet looking upstream.

Downstream channel aligned roughly perpendicular to roadway. Moderate scour hole downstream of the south pier.

PHOTO 8

PHOTO 9

9/30/2020

Active channel width approximately 24-feet. Banks stable and well vegetated.

Pool-riffle dominant bed form. Cobble-gravel streambed material.

Fish Creek Bridge north (left) abutment.

Fish Creek Bridge south (right) abutment.

Fish Creek upstream of bridge.

Erosion observed at the right abutment.

Slight erosion visible on the left abutment.

PHOTO 11

PHOTO 12

9/30/2020

Fish Creek downstream of bridge.

Streambed material typically transported by stream flows. Tape 4'-2". D50 approximately 6.7" and D100 approximately 24".

Fish Creek downstream of bridge.

Streambed material typically transported by stream flows. Tape 4'-8". D50 approximately 6.7" and D100 approximately 24".

Fish Creek upstream of bridge.

Active channel width approximately 24-feet. Banks stable and well vegetated.

Pool-riffle dominant bed form. Cobble-gravel streambed material.

1430-007 Fish Creek Bridge - StreamStats Report

Parameter Code Parameter Description Value Unit

CONTDA Area that contributes flow to a point on a stream 14.2 square miles

SLOP50_30M Percent area with slopes greater than 50 percent from 30-meter DEM. 18.3 percent

PRECIP Mean Annual Precipitation 37.36 inches

FOREST Percentage of area covered by forest 93.8 percent

BSLDEM30M Mean basin slope computed from 30 m DEM 27.1 percent

ET0306MOD Spring (March-June) mean monthly evapotranspiration (2001-2011), MODIS 1.75 inches

ELEVMAX Maximum basin elevation 6630 feet

Peak-Flow Statistics Parameters[NW Region BasinC 2015 5019F]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 14.2 square miles 2.43 1560

Peak-Flow Statistics Flow Report[NW Region BasinC 2015 5019F]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu SEp

1.5 Year Peak Flood 167 ft^3/s 34.6 807 115

2 Year Peak Flood 213 ft^3/s 57.9 784 88.9

2 33 Year Peak Flood 238 ft^3/s 71.3 794 80.4

5 Year Peak Flood 396 ft^3/s 170 925 52.8

10 Year Peak Flood 596 ft^3/s 334 1060 34.4

25 Year Peak Flood 1020 ft^3/s 844 1230 9.1

50 Year Peak Flood 1560 ft^3/s 1230 1970 11.3

100 Year Peak Flood 2350 ft^3/s 1770 3120 13.6

200 Year Peak Flood 3520 ft^3/s 2530 4900 16

500 Year Peak Flood 5970 ft^3/s 4010 8890 19.3

Region ID: MT Workspace ID: MT20201030154859110000 Clicked Point (Latitude, Longitude): 48.54975, -113.98502 Time: 2020-10-30 08:49:19 -0700

Page 2 of 5StreamStats

Peak-Flow Statistics Citations

Sando, Roy, Sando, S.K., McCarthy, P.M., and Dutton, D.M.,2016, Methods for estimating peak-flow frequencies at ungaged sites in Montana based on data through water year 2011: U.S. Geological Survey Scientific Investigations Report 2015–5019–F, 30 p.

(https://doi.org/10.3133/sir20155019)

Low-Flow Statistics Parameters[NW Region LowFlow GLS 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 14.2 square miles 7.74 1560

SLOP50_30M Slopes_gt_50pct_from_30m_DEM 18.3 percent 0.06 66

Low-Flow Statistics Flow Report[NW Region LowFlow GLS 2015 5019G]

PIl : Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other - - see report)

Statistic Value Unit PIl PIu SEp

7 Day 10 Year Low Flow 0.924 ft^3/s 0.226 3.77 78.1

Low-Flow Statistics Citations

McCarthy, P.M., Sando, Roy, Sando, S.K., and Dutton, D.M.,2016, Methods for estimating streamflow characteristics at ungaged sites in western Montana based on data through water year 2009: U.S. Geological Survey Scientific Investigations Report 2015–5019–G, 19 p.

(https://doi.org/10.3133/sir20155019)

Flow-Duration Statistics Parameters[NW Region Annual MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 14.2 square miles 7.74 1560

PRECIP Mean Annual Precipitation 37.36 inches 20.7 83.2

Flow-Duration Statistics Flow Report[NW Region Annual MeanDur 2015 5019G]

Statistic Value Unit

20 Percent Duration 28 ft^3/s

80 Percent Duration 5.05 ft^3/s

Flow-Duration Statistics Citations

McCarthy, P.M., Sando, Roy, Sando, S.K., and Dutton, D.M.,2016, Methods for estimating streamflow characteristics at ungaged sites in western Montana based on data through water year 2009: U.S. Geological Survey Scientific Investigations Report 2015–5019–G, 19 p.

(https://doi.org/10.3133/sir20155019)

Annual Flow Statistics Parameters[NW Region Annual MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 14.2 square miles 7.74 1560

PRECIP Mean Annual Precipitation 37.36 inches 20.7 83.2

Annual Flow Statistics Flow Report[NW Region Annual MeanDur 2015 5019G]

Statistic Value Unit

Median Annual Flow 12 ft^3/s

Mean Annual Flow 19.2 ft^3/s

Annual Flow Statistics Citations

McCarthy, P.M., Sando, Roy, Sando, S.K., and Dutton, D.M.,2016, Methods for estimating streamflow characteristics at ungaged sites in western Montana based on data through water year 2009: U.S. Geological Survey Scientific Investigations Report 2015–5019–G, 19 p.

(https://doi.org/10.3133/sir20155019)

Page 3 of 5StreamStats

Monthly Flow Statistics Parameters[NW Region Season3 MeanDur 2015 5019G]

CONTDA Contributing Drainage Area 14.2 square miles 7.74 1560

PRECIP Mean Annual Precipitation 37.36 inches 20.7 83.2

Monthly Flow Statistics Parameters[NW Region Season1 MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 14.2 square miles 7.74 1560

PRECIP Mean Annual Precipitation 37.36 inches 20.7 83.2

Monthly Flow Statistics Parameters[NW Region Season2 MeanDur 2015 5019G]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 14.2 square miles 7.74 1560

PRECIP Mean Annual Precipitation 37.36 inches 20.7 83.2

Monthly Flow Statistics Flow Report[NW Region Season3 MeanDur 2015 5019G]

Statistic Value Unit

November Mean Flow 7.91 ft^3/s

December Mean Flow 6.34 ft^3/s

January Mean Flow 5.02 ft^3/s

February Mean Flow 5.79 ft^3/s

Monthly Flow Statistics Flow Report[NW Region Season1 MeanDur 2015 5019G]

Statistic Value Unit

March Mean Flow 6.28 ft^3/s

April Mean Flow 14 ft^3/s

May Mean Flow 35.5 ft^3/s

June Mean Flow 43 ft^3/s

Monthly Flow Statistics Flow Report[NW Region Season2 MeanDur 2015 5019G]

Statistic Value Unit

July Mean Flow 17.8 ft^3/s

August Mean Flow 8.17 ft^3/s

September Mean Flow 6.71 ft^3/s

October Mean Flow 9.19 ft^3/s

Monthly Flow Statistics Flow Report[Area-Averaged]

Statistic Value Unit

November Mean Flow 7.91 ft^3/s

December Mean Flow 6.34 ft^3/s

January Mean Flow 5.02 ft^3/s

February Mean Flow 5.79 ft^3/s

March Mean Flow 6.28 ft^3/s

April Mean Flow 14 ft^3/s

May Mean Flow 35.5 ft^3/s

June Mean Flow 43 ft^3/s

July Mean Flow 17.8 ft^3/s

August Mean Flow 8.17 ft^3/s

September Mean Flow 6.71 ft^3/s

October Mean Flow 9.19…