AK RainbowCreek AOP Report Final.pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

SWAN LAKE / SWANSON RIVER ROAD

RAINBOW LAKE AOP HYDRAULICS REPORT

To: Stacy Bluhm, WFLHD Project Manager

From: James Neighorn, P.E. and Vernon Bevan, WFLHD Hydraulics Engineer

Date: June 20, 2023

Project: Swan Lake / Swanson River Road – AK FWS Kenai 74525(1)

Background

The Kenai National Wildlife Refuge (NWR) is rehabilitating Swan Lake Road and Swanson River Road to improve access to public recreation along the corridors, increase transportation safety, and to mitigate damage to wildlife and aquatic organism passage. As part of the project the NWR is replacing a culvert located on Swanson River Road near the outfall of Rainbow Lake, Kenai National Wildlife Refuge, Kenai

Peninsula Borough, Alaska. The Kenai NWR will maintain the new structure. Western Federal Lands

Highway Division (WFLHD) is designing the replacement structure. Recommendations for the proposed aquatic organism passage (AOP) structure design are presented.

AOP Design Criteria

The proposed AOP structure has been designed following the requirements Culvert Design Guidelines for

Ecological Function (U.S. Fish and Wildlife 2021) and per Stream Simulation: An Ecological Approach to

Providing Passage for Aquatic Organisms at Road-Stream Crossings (USDA-Forest Service 2008). These documents provide design methodologies intended to mimic natural stream processes within the culvert.

Sediment transport, debris conveyance and streambed morphology within the culvert should replicate these processes as they occur in the natural channel upstream and downstream of the culvert. Determination of the high and low fish passage design flows, water velocity, and water depth is not required for this method since the stream hydraulic characteristics within the culvert are intended to replicate the stream conditions upstream and downstream of the crossing. AOP culvert design utilizes streambed materials and sizes which occur in the natural channel, providing similar channel complexity, flow depth, flow velocities, and resting areas.

USFW Alaska Fish Passage Program (USFW/AFPP) Guidelines

The AOP design for the Rainbow Lake outfall crossing is consistent with the 2021 U.S. Fish and Wildlife

(USFW) Service design guidelines. The 2021 document generally follows the U.S. Forest Service stream simulation approach with certain modifications. The basis for AOP design is the geomorphic analog method. The underlying philosophy of the geomorphic analog method is similar to the stream simulation approach. However, many of the design criteria are based on the 100-year flood event as opposed to a specifically selected design flood. The following USFW/AFPP requirements have been incorporated into the AOP design:

Flood and Debris Conveyance: Culvert capacity is designed to accommodate the 100-year recurrence flood without interfering with the functioning of the floodplain while providing adequate clearance above the flood stage for expected debris. The headwater depth to opening depth ratio should be less than 0.8.

Crossing Location: Crossing structure is placed within the pre-development natural channel alignment

Memo to: Stacy Bluhm, WFLHD Project Manager

June 2023 wherever possible.

Culvert Width: Must accommodate the design channel bankfull width plus additional width for construction of stable bank rocks along both sides of the channel inside the culvert. All culverts will meet design requirements for a 6-foot minimum diameter.

Channel Vertical Clearance: Clearance from bed to ceiling must be at least 4-feet to allow for ease of construction, maintenance, and debris removal. Where possible, clearance will be 5-feet or greater.

Channel Slope: Reconstructed streambed within the culvert approximates the average slope of the stream reference reach. The slope should not deviate by more than 25% from the natural stream slope of the reference reach.

Embedment: Bottoms of round culverts should be buried below the streambed thalweg a minimum of

40% of the pipe diameter. Box or pipe arch culverts should be buried a minimum of 20% of the culvert’s rise.

Maximum Length of Road Crossing: Length should be less than 150-feet.

Fill Materials: Fill materials are generally comprised of sediment similar in size composition to natural bed materials that form the natural stream channel above and below the road crossing. Larger material is added to assist grade retention and provide resting areas for migrating fish. A dense, well-graded mixture is specified, with washing in of fines between constructed lifts, to encourage the stream to flow on the surface.

Fill/substrate material for culverts without an adequate sediment supply, such as those situated below a lake or wetland, should be designed to resist the predicted critical shear forces of the 100-year flood.

Water Depth and Velocity: Bankfull water depths and velocities in the culvert must closely resemble those existing reference reach as specified in the 2021 USFW Service guidance document.

Rainbow Lake AOP Culvert

United States Fish and Wildlife Service (USFWS) has determined that the Rainbow Lake outfall crossing requires an AOP structure (60°43’2” N, 150°49’3” W, NAD1983). Federal Lands Highway Division conducted field reconnaissance of the crossing in 2019 and 2021.

The crossing is located on an unnamed tributary of the Swanson River, approximately 1-mile upstream from their confluence and just downstream of the Rainbow Lake outfall (Figure 1). The unnamed tributary crosses Swanson River Road through an existing 48-inch diameter CMP. The crossing is located just 100-feet downstream from the outfall of Rainbow Lake (Photo 1). Given the close proximity to Rainbow Lake, the upstream reach is heavily influenced by lake levels; therefore, observations and measurements within the upstream reach do not reflect channel forming processes downstream of the crossing. The upstream reach has a bankfull width of roughly 9-feet (Photo 3). The observed channel was relatively straight, wide, and slow moving. Woody debris was observed within the reach, likely supplied from the lake and adjacent channel banks (Photos 1 and 3). The channel immediately upstream and downstream of the road is quite flat with a slope of approximately 0.5% or less adjacent to the crossing.

Downstream of the crossing, the channel slope is roughly 2.2%. Riffle-pool is the dominant bed form, with boulder and woody debris controlling the stream profile (Photos 6 and 7). The measured bankfull width in the downstream reach ranged between 3 to 4-feet (Photo 5). Bankfull depths were measured between 0.6 to 1.2 feet. Bed material is mostly sand and cobble with some gravel and boulders (Photo 9). Streambed pebble counts were performed at two channel riffles. The data was processed using the FHWA Hydraulic

Toolbox, version 4.2, to compute the resulting gradation: D100 10.0-inches, D85 4.0-inches, D50 0.2-inches, and D15 0.05-inches (Figure 3). The stream appears stable with frequent woody debris vertical controls, a low accessible floodplain, and well vegetated banks (Photo 6). The channel downstream of the crossing is unconfined, with a flood-prone width estimated at roughly 100-feet. Based on observed field conditions, the stream can likely carry a moderate amount of small to moderate sized woody debris. Stream flow when fish passage is needed may be low.

The existing crossing is currently served by a 48-inch CMP that appears to be in critically poor condition.

The pipe has a rusted bottom and both inverts appear to have been displaced upwards (Photos 2, 4 and 8).

The roadway elevation provides adequate cover over the existing culvert. The existing culvert diameter is similar in size to the downstream bankfull width and issues typically associated with an undersized crossing, such as a large scour hole at the culvert outfall, were not observed at the site. The existing culvert was situated perpendicular to the roadway and was well aligned with the stream thalweg.

Recommendations:

The existing pipe is in poor condition and a new pipe is needed at the crossing. Field conditions indicate that the existing 48-inch pipe is likely the appropriate size given the hydrologic and hydraulic conditions at the crossing; however, a larger pipe will be necessary to provide space for a natural channel bottom and a small accessible floodplain bench. The close proximity of the crossing to Rainbow Lake will impact the amount and type of sediment supplied to the culvert. The designed streambed sediment will need to account for limited sediment supply by augmenting the streambed gradation with larger cobbles and boulders.

During low flow conditions, streamflow within the culvert can go sub-surface where the bed consists of larger, loosely compacted material with significant voids. To avoid creation of low flow subsurface conditions, material placed within the proposed culvert will need to have voids adequately filled.

• Install a 122-foot long, corrugated metal round culvert with a 9-foot diameter on the existing alignment.

• Place the culvert at a 0.48% slope to match channel slopes at the crossing by setting the inverts at elevation 213.68-feet upstream and at elevation 213.10-feet downstream (project datum).

• Embed the culvert a minimum of 4 feet and backfill the culvert interior with streambed material conserved during excavation of the culvert. If the conserved streambed material quantity is insufficient for backfilling the culvert, use material similar to the natural streambed material.

Streambed material will be augmented with Class B gradation cobbles specified in the attached

Special Contract Requirements (SCR) and Gradation Stability Calculations to provide a dynamically stable substrate.

• Allow clearance for debris passage and maintenance access by providing 5 feet of clearance from the crown of the culvert and the installed bed material and providing a headwater to depth of opening ratio (HW/D) of less than 0.8.

• Construct a channel with a bankfull width of 6 feet and a bankfull depth of 1 foot including a low flow channel and streambanks inside the culvert to provide resting opportunities for fish.

• Install 5 rock weirs spaced at 24-foot intervals to help maintain banks and channel shape.

• Install 5 round boulders, approximately 18-inches in diameter, for inducing channel migration and providing low velocity fish resting areas.

• Install concrete collars to mitigate the influence of frost heaving at pipe ends.

• Install Class 3 riprap (FHWA FP-14), minimum 3 feet thick, at the inlet and outlet for controlling erosion near the culvert.

Construction

The Alaska Department of Fish and Wildlife instream work period is May 15 to July 15. Temporary flow deflectors placed for isolating the work area and diverting the stream flow must have a minimum height of

2-feet above the stream bottom and be stable assuming 2.5-feet per second parallel flow. Use plastic-lined channels or pipes for temporally conveying stream flow through the construction area. Protect the outfalls from erosion. Ensure fish can pass smoothly through the diversion. Temporary stream diversions in place must provide an equivalent capacity to a 2-foot diameter pipe or demonstrate a minimum flow capacity equal to the 2-year discharge (16-cfs). Before installing the flow deflectors, remove fish from the work area to the level and methods meeting the 2009 ADF&G and FHWA Fish Habitat MOU requirements.

Full construction area dewatering is expected up to the groundwater level for excavation and installing the culvert, streambed material, backfill, and riprap. Water pumped from work area must be discharged at an upland treatment area near the site.

Temporary access route adjacent to the road embankment is needed for installing flow barriers, removing the channel debris, and completing culvert inlet, interior, and outlet work.

Stream Impacts

The proposed fish passage culvert is expected to dramatically improve stream flow conveyance, sediment transport, and woody debris transport to a level comparable to reaches upstream and downstream of the culvert. A moderate amount of turbidity and sediment is expected to be released when the flow barriers are removed, and stream flow is introduced into the newly constructed culvert. The amount of turbidity and sediment will be reduced by removing the flow barriers gradually introducing the stream flow over an extended two to three-hour time.

Operation and Maintenance

Scour or aggradation of the streambed is also expected to occur to some extent, as would be expected for the natural stream. Monitoring at regular intervals, and ideally during flood events, will be especially important during the first few years to ensure that excessive debris accumulation, scour, or aggradation does not impair passage through the culvert. Increase the frequency of culvert inspections and debris removal for the first three years. Fish boulders placed within the culvert and stream channel should be inspected annually and after each extreme flood event to ensure effective backwater and bed retention.

Replace or reposition dislodged rock or boulders. Additional rock may need to be installed to correct erosion or channel degradation. Riprap placed at the culvert inlet and outlet should be inspected annually and after each extreme flood event. Replace or reposition dislodged stone.

Floodplain and Flood-rise Impacts

Flood limits and elevations have not been mapped by the National Flood Insurance Program for the site.

The proposed culverts will improve hydraulic conveyance and is not expected to negatively impact flooding at the site.

Hydrology

The USGS StreamStats (version 4) web-based application was used for delineating the watershed and calculating drainage area (0.9 sq. miles) and mean annual precipitation (17-inches). Since delineations made by StreamStats can include inaccuracies for smaller watersheds and flat areas, the delineated watershed was verified by comparing it to both USGS TOPO maps and Digital Terrain Maps produced by the Alaska

Division of Geological and Geophysical Surveys. No significant deviations that would impact flow estimates were found.

Peak discharges were estimated with StreamStats (Table 1) using USGS regression equations from

Magnitude and Frequency at Gaged and Ungaged Sites on Streams in Alaska and Conterminous Basins in

Canada (USGS WRIR 2016-5024). The watershed is mostly comprised of forested land and surface water from Rainbow Lake (Figure 2). Rainbow Lake makes up a significant portion of the basin area and its presence could influence the amount of runoff generated by the watershed. The lake could increase runoff by providing a large impervious surface, or conversely, the lake could act to attenuate flows. Hydraulic modeling of the channel and the existing 48-inch culvert indicate that the flows derived from the USGS regression equations are likely reasonable estimates of the basin’s hydrology. A summary of peak discharges and their corresponding water depths at the culvert inlet are presented in Table 2.

Dominant flooding is from snow melt. Larger floods typically occur in April and May. Rain-on-snow flood events can occur in October through December. Lower flows typically occur from January to February and

July through September.

Culvert Hydraulics

Water surface profiles and culvert capacities were estimated using the FHWA Culvert Hydraulics Analysis

Program, HY-8, version 7.7 (results attached). Floods larger than the 2-year were analyzed assuming culvert slope of 0.48 percent and Manning’s Roughness coefficient of 0.035 for the channel bottom and 0.024 for the culvert sides and top.

The computed outlet tailwater depth of 0.8 feet for the 2-year discharge was compared with the bankfull channel design depth of 1.0 and found to be within the measured range of the 0.6 to 1.2 feet in the natural channel.

Hydraulic results are included in the attachments with headwater depths and ratios shown in Table 2.

Attachments: Table 1 - Peak Discharge Estimates

Table 2 – Headwater Depths and Ratios

Figures 1, 2, and 3

Photographs

HY-8 Calculations

USGS StreamStats Report

Drawings

Special Contract Requirements and Gradation Stability Calculations

Tables

Table 1. Peak Discharges Estimates Peak Annual Floods Discharge (ft3/2)

2-Year 16 5-Year 31

10-Year 43 25-Year 61 50-Year 76

100-Year 92 200-Year 109 500-Year 134

Table 2. Peak Discharges and Water Depths Peak Annual

Floods Discharge (ft3/2) Headwater Depth (HW)

(ft)

HW/D

(D= 5.0 ft) 2-Year 16 0.89 0.18

50-Year 76 2.42 0.48 100-Year 92 2.74 0.55

D = Distance between culvert crown and streambed

Image date: 4/17/2011

Project AOP Culvert Site Location

Project Area Location

USGS Topographic Maps on Google Earth

N

FIGURE 1

RAINBOW LAKE

AOP CULVERT

SITE LOCATION

Rainbow Lake AOP

2500 feet0

Rainbow Lake

Map printed from Google Earth, Image date 7/14/2017.

N

DA = 0.9 sq. mi.

FIGURE 2

RAINBOW LAKE

AOP CULVERT

DRAINAGE AREA

0 2500 feet

Photos

PHOTO 1

7/27/2021

PHOTO 2

7/27/2021

PHOTO 3

6/5/2019

Rainbow Lake AOP

Looking upstream towards Rainbow Lake. Woody debris observed within channel. Small, straight channel with a bankfull width approximately 9 to 10-feet wide.

Existing 48" culvert has rusted invert at inlet. Appears that the ends of the existing culvert have been displaced upwards, possibly due to frost heaving.

Channel upstream of culvert.

Upstream of culvert Inlet.

Looking upstream. Roughly 100' upstream of the crossing is the outfall of Rainbow Lake.

Culvert Inlet.

PHOTO 4

6/5/2019

PHOTO 5

6/5/2019

PHOTO 6

6/5/2019

Looking downstream from existing culvert outlet. Small, low sinuosity channel with a bankfull width approximately 3 to 4-feet wide.

Structure downstream of the culvert.

Rainbow Lake AOP

Example of woody debris check structure within natural channel. Well vegetated adjacent bankfull benches.

Culvert outlet.

Existing 48" culvert with rusted invert at outlet. Appears that the ends of the existing culvert have been displaced upwards, possibly due to frost heaving.

Channel downstream of culvert.

PHOTO 7

6/5/2019

PHOTO 8

7/27/2021

PHOTO 9

6/5/2019

Structure downstream of the culvert.

Streambed material.

Example of woody debris check structure within natural channel.

Picture of streambed sediment showing gravel, cobble, and sand.

Inside of existing 48" culvert.

Rusted bottom and pipe is out of round.

Rainbow Lake AOP

HY-8 Culvert Analysis Report - Proposed AOP Crossing Discharge Data Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 16.00 cfs

Design Flow: 76.00 cfs

Maximum Flow: 92.00 cfs

Table 1 - Summary of Culvert Flows at Crossing: Rainbow Lake Headwater Elevation (ft)

Total Discharge (cfs)

Rainbow Lake Discharge (cfs)

Roadway Discharge (cfs)

Iterations

218.64 16.00 16.00 0.00 1

218.82 23.60 23.60 0.00 1

219.06 31.20 31.20 0.00 1

219.26 38.80 38.80 0.00 1

219.45 46.40 46.40 0.00 1

219.63 54.00 54.00 0.00 1

219.80 61.60 61.60 0.00 1

219.96 69.20 69.20 0.00 1

220.10 76.00 76.00 0.00 1

220.27 84.40 84.40 0.00 1

220.42 92.00 92.00 0.00 1

236.00 610.51 610.51 0.00 Overtopping

Rating Curve Plot for Crossing: Rainbow Lake

Culvert Data: Rainbow Lake

Table 1 - Culvert Summary Table: Rainbow Lake Total Discharge (cfs)

Culvert Discharge (cfs)

Headwater Elevation (ft)

Inlet Control Depth (ft)

Outlet Control Depth (ft)

Flow Type

Normal Depth (ft)

Critical Depth (ft)

Outlet Depth (ft)

Tailwater Depth (ft)

Outlet Velocity (ft/s)

Tailwater Velocity (ft/s)

16.00 cfs 16.00 cfs 218.64 0.96 0.892 3- M2t

0.78 0.46 0.76 0.76 2.35 4.42

23.60 cfs 23.60 cfs 218.82 1.13 1.143 3- M2t

1.00 0.60 0.95 0.95 2.76 4.99

31.20 cfs 31.20 cfs 219.06 1.29 1.379 3- M1t

1.19 0.72 1.25 1.25 2.80 4.34

38.80 cfs 38.80 cfs 219.26 1.45 1.583 3- M1t

1.37 0.84 1.38 1.38 3.15 4.34

46.40 cfs 46.40 cfs 219.45 1.60 1.772 3- M2t

1.54 0.94 1.48 1.48 3.52 4.41

54.00 cfs 54.00 cfs 219.63 1.75 1.949 3- M2t

1.70 1.04 1.56 1.56 3.89 4.50

61.60 cfs 61.60 cfs 219.80 1.90 2.117 3- M2t

1.86 1.14 1.63 1.63 4.24 4.60

69.20 cfs 69.20 cfs 219.96 2.05 2.279 3- M2t

2.01 1.23 1.69 1.69 4.59 4.69

76.00 cfs 76.00 cfs 220.10 2.17 2.419 3- M2t

2.15 1.31 1.75 1.75 4.90 4.77

84.40 cfs 84.40 cfs 220.27 2.33 2.588 3- M2t

2.31 1.40 1.81 1.81 5.27 4.86

92.00 cfs 92.00 cfs 220.42 2.46 2.737 3- M2t

2.46 1.48 1.86 1.86 5.60 4.95

Culvert Barrel Data Culvert Barrel Type Straight Culvert

Inlet Elevation (invert): 217.68 ft, Outlet Elevation (invert): 217.10 ft

Culvert Length: 122.00 ft, Culvert Slope: 0.0048

Culvert Performance Curve Plot: Rainbow Lake

Site Data - Rainbow Lake Site Data Option: Culvert Invert Data

Inlet Station: 0.00 ft

Inlet Elevation: 213.68 ft

Outlet Station: 122.00 ft

Outlet Elevation: 213.10 ft

Number of Barrels: 1

Culvert Data Summary - Rainbow Lake Barrel Shape: Circular

Barrel Diameter: 9.00 ft

Barrel Material: Corrugated Steel

Embedment: 48.00 in

Barrel Manning's n: 0.0240 (top and sides)

Manning's n: 0.0350 (bottom)

Culvert Type: Straight

Inlet Configuration: Beveled Edge (Ke=0.2)

Inlet Depression: None

Tailwater Data for Crossing: Rainbow Lake

Table 2 - Downstream Channel Rating Curve (Crossing: Rainbow Lake) Flow (cfs) Water

Surface Elev (ft)

Velocity (ft/s)

Depth (ft) Shear (psf) Froude Number

16.00 217.86 0.76 4.42 1.04 0.96

23.60 218.05 0.95 4.99 1.31 0.98

31.20 218.35 1.25 4.34 1.71 0.98

38.80 218.48 1.38 4.34 1.89 0.98

46.40 218.58 1.48 4.41 2.03 0.99

54.00 218.66 1.56 4.50 2.14 1.00

61.60 218.73 1.63 4.60 2.24 1.00

69.20 218.79 1.69 4.69 2.33 1.01

76.00 218.85 1.75 4.77 2.40 1.02

84.40 218.91 1.81 4.86 2.48 1.02

92.00 218.96 1.86 4.95 2.55 1.03

Tailwater Channel Data - Rainbow Lake Tailwater Channel Option: Irregular Channel

Channel Slope: Irregular Channel

User Defined Channel Cross-Section Coord No. Station (ft) Elevation (ft) Manning's n 1 0.00 225.00 0.0580 2 5.00 220.00 0.0350 3 27.00 218.10 0.0350 4 28.00 217.10 0.0350 5 32.00 217.10 0.0350 6 33.00 218.10 0.0350 7 55.00 220.00 0.0580 8 60.00 225.00 0.0580

Roadway Data for Crossing: Rainbow Lake Roadway Profile Shape: Constant Roadway Elevation

Crest Length: 100.00 ft

Crest Elevation: 236.00 ft

Roadway Surface: Gravel

Roadway Top Width: 30.00 ft

HY-8 Culvert Analysis Report - Existing Conditions

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 16.00 cfs

Design Flow: 76.00 cfs

Maximum Flow: 109.00 cfs

Table 1 - Summary of Culvert Flows at Crossing: Rainbow Lake Existing Conditions

Headwater Elevation (ft)

Total Discharge (cfs)

Rainbow Lake Discharge (cfs)

Roadway Discharge (cfs)

Iterations

220.79 16.00 16.00 0.00 1

221.32 25.30 25.30 0.00 1

221.79 34.60 34.60 0.00 1

222.23 43.90 43.90 0.00 1

222.65 53.20 53.20 0.00 1

223.06 62.50 62.50 0.00 1

223.71 76.00 76.00 0.00 1

224.00 81.10 81.10 0.00 1

224.72 90.40 90.40 0.00 1

225.53 99.70 99.70 0.00 1

226.35 109.00 109.00 0.00 1

235.00 182.39 182.39 0.00 Overtopping

Rating Curve Plot for Crossing: Rainbow Lake Existing Conditions

Culvert Data: Rainbow Lake

Table 1 - Culvert Summary Table: Rainbow Lake

Total Discharge (cfs)

Culvert Discharge (cfs)

Headwater Elevation (ft)

Inlet Control Depth (ft)

Outlet Control Depth (ft)

Flow Type

Normal Depth (ft)

Critical Depth (ft)

Outlet Depth (ft)

Tailwater Depth (ft)

Outlet Velocity (ft/s)

Tailwater Velocity (ft/s)

16.00 cfs 16.00 cfs 220.79 1.73 1.893 2-M2c 1.42 1.17 1.17 0.63 5.21 1.25

25.30 cfs 25.30 cfs 221.32 2.22 2.430 2-M2c 1.83 1.49 1.49 0.71 5.95 0.96

34.60 cfs 34.60 cfs 221.79 2.67 2.899 2-M2c 2.20 1.75 1.75 0.76 6.55 0.96

43.90 cfs 43.90 cfs 222.23 3.09 3.334 2-M2c 2.57 1.98 1.98 0.80 7.07 0.99

53.20 cfs 53.20 cfs 222.65 3.50 3.753 2-M2c 2.97 2.19 2.19 0.84 7.55 1.03

62.50 cfs 62.50 cfs 223.06 3.93 4.172 7-M2c 3.54 2.38 2.38 0.88 8.00 1.07

76.00 cfs 76.00 cfs 223.71 4.58 4.821 7-M2c 4.00 2.64 2.64 0.92 8.64 1.13

81.10 cfs 81.10 cfs 224.00 4.85 5.103 7-M2c 4.00 2.73 2.73 0.94 8.88 1.15

90.40 cfs 90.40 cfs 224.72 5.38 5.826 7-M2c 4.00 2.88 2.88 0.97 9.33 1.18

99.70 cfs 99.70 cfs 225.53 5.95 6.633 7-M2c 4.00 3.03 3.03 1.00 9.78 1.22

109.00 cfs 109.00 cfs 226.35 6.59 7.460 7-M2c 4.00 3.16 3.16 1.03 10.25 1.26

Culvert Barrel Data

Culvert Barrel Type Straight Culvert

Inlet Elevation (invert): 218.89 ft, Outlet Elevation (invert): 218.19 ft

Culvert Length: 122.18 ft, Culvert Slope: 0.0058

Culvert Performance Curve Plot: Rainbow Lake

Water Surface Profile Plot for Culvert: Rainbow Lake

Site Data - Rainbow Lake

Site Data Option: Culvert Invert Data

Inlet Station: 0.00 ft

Inlet Elevation: 218.89 ft

Outlet Station: 122.18 ft

Outlet Elevation: 218.19 ft

Number of Barrels: 1

Culvert Data Summary - Rainbow Lake

Barrel Shape: Circular

Barrel Diameter: 4.00 ft

Barrel Material: Corrugated Steel

Embedment: 0.00 in

Barrel Manning's n: 0.0240

Culvert Type: Straight

Inlet Configuration: Thin Edge Projecting (Ke=0.9)

Inlet Depression: None

Tailwater Data for Crossing: Rainbow Lake Existing Conditions

Table 2 - Downstream Channel Rating Curve (Crossing: Rainbow Lake Existing Conditions)

Flow (cfs) Water Surface Elev (ft)

Velocity (ft/s) Depth (ft) Shear (psf) Froude Number

16.00 218.75 0.63 1.25 0.19 0.70

25.30 218.83 0.71 0.96 0.21 0.45

34.60 218.88 0.76 0.96 0.23 0.39

43.90 218.92 0.80 0.99 0.24 0.36

53.20 218.96 0.84 1.03 0.25 0.35

62.50 219.00 0.88 1.07 0.26 0.34

76.00 219.04 0.92 1.13 0.28 0.33

81.10 219.06 0.94 1.15 0.28 0.33

90.40 219.09 0.97 1.18 0.29 0.33

99.70 219.12 1.00 1.22 0.30 0.33

109.00 219.15 1.03 1.26 0.31 0.33

Tailwater Channel Data - Rainbow Lake Existing Conditions

Tailwater Channel Option: Irregular Channel

Channel Slope: Irregular Channel

User Defined Channel Cross-Section

Coord No. Station (ft) Elevation (ft) Manning's n

1 0.00 225.00 0.0580

2 5.00 218.80 0.0580

3 94.00 218.65 0.0580

4 95.50 218.12 0.0330

5 100.00 218.12 0.0330

6 105.50 218.12 0.0330

7 106.00 218.65 0.0580

8 195.00 218.80 0.0580

9 200.00 225.00 0.0000

Roadway Data for Crossing: Rainbow Lake Existing Conditions

Roadway Profile Shape: Constant Roadway Elevation

Crest Length: 100.00 ft

Crest Elevation: 235.00 ft

Roadway Surface: Gravel

Roadway Top Width: 30.00 ft

Rainbow Lake

Basin Characteristics

Parameter Code Parameter Description Value Unit

DRNAREA Area that drains to a point on a stream 0.9 square miles

PRECPRIS00 Basin average mean annual precipitation for 1971 to 2000 from PRISM

17 inches

Region ID: AK Workspace ID: AK20191001192623560000 Clicked Point (Latitude, Longitude): 60.71720, -150.81773 Time: 2019-10-01 12:26:43 -0700

Page 2 of 4StreamStats

10/1/2019https://streamstats.usgs.gov/ss/

Peak-Flow Statistics Parameters[Peak Areas less than 1000 sqmi SIR 2016 5024]

Parameter Code Parameter Name Value Units

Min Limit

Max Limit

DRNAREA Drainage Area 0.9 square miles

0.4 1000

PRECPRIS00 Mean Annual Precip PRISM 1971 2000

17 inches 8 280

Peak-Flow Statistics Flow Report[Peak Areas less than 1000 sqmi SIR 2016 5024]

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

2 Year Peak Flood 15.7 ft^3/s 5.44 45.2 70.8

5 Year Peak Flood 30.4 ft^3/s 10.8 86 69.1

10 Year Peak Flood 42.9 ft^3/s 15.2 121 69.2

25 Year Peak Flood 60.9 ft^3/s 21.1 176 71.2

50 Year Peak Flood 75.6 ft^3/s 25.6 223 72.8

100 Year Peak Flood 91.9 ft^3/s 30.5 277 74.6

200 Year Peak Flood 109 ft^3/s 35 340 77.4

500 Year Peak Flood 134 ft^3/s 40.7 439 81.9

Peak-Flow Statistics Citations

Curran, J.H., Barth, N.A., Veilleux, A.G., and Ourso, R.T.,2016, Estimating Flood Magnitude and Frequency at Gaged and Ungaged Sites on Streams in Alaska and Conterminous Basins in Canada, Based on Data through Water Year 2012: U.S.

Geological Survey Scientific Investigations Report 2016-5024, 47 p.

(http://dx.doi.org/10.3133/sir20165024http://dx.doi.org/10.3133/sir20165024)

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.

Page 3 of 4StreamStats

10/1/2019https://streamstats.usgs.gov/ss/

SCALE IN FEET

10 0 10 20 30 40

OUTLETINLETPIPEHYDRAULIC INFORMATION

0 20 40 60 8020406080

LENGTH: 122 ft

PIPE SLOPE: 0.0048 ft/ft

HEADWALL: Conc./Riprap

FLOWLINE SLOPE: 0.0048 ft/ft

100 120100120140

Q : 16 CFS

Q : 76 CFS

BANKFULL CHANNEL WIDTH: 4.0 ft D/S to 9.0 ft U/S

TYPE: Metal round culvert SPAN: 9.0 ft RISE: 9.0 ft

LOWER BEVEL HEIGHT: 2.25 ft LOWER BEVEL HEIGHT: 2.25 ft

BEVEL: 1.5h : 1v

HEADWALL: Conc./Riprap

BEVEL: 1.5h : 1v

Q : 92 CFS

INV N/E/EL: 2455045.45/1494037.42/213.68' /1493977.26/213.10'INV N/E/EL: 2454939.30

WALL THICKNESS: NA

:1

Existing ground

Flow

Flow

Remove exisiting 48" CMP

HW : 220.42 ft

Creek at Rainbow Lake

N

LC

OHW : 218.64 ft

Slope 0.48%

Line to be constructed

BURIAL DEPTH: 4.0 ft BURIAL DEPTH: 4.0 ft

1:1

New culvert centerline metal round culvert.

9 foot diameter

402+60.00402+23.73, 55.51 LT

402+88.08, 48.34' RT

PLAN AND PROFILE

RAINBOW LAKE CULVERT

[1]method B, class 3

Placed riprap

[1]method B, class 3

Placed riprap

[1]method B, class 3

Placed riprap

[1]method B, class 3

Placed riprap detail Sheet G.13.

Backfill with streambed material per

FOOTNOTE:

See Sheet G.11 for riprap details.[1]

G.4

STATE PROJECT

NUMBER

SHEET

AK FWS KNA 74525(1)

J N e ig h o r n

/2

/2

C h e c k e d b y

D e s ig n e d b y

In t_ ft

D c p w w o r k \d

\a k r k e n a i1 h .d g n

Road centerline

Channel elev. 217.10

Channel elev. 217.68

Channel flowline

Road grade

:1

A

M

J u ly

Rainbow Lake per detail sheet G.14

Install rock weirs at 24' spacing

End channel grading

Concrete collar

Begin channel grading

Concrete collar

Begin channel grading

Concrete collar

Cut and fill limits (typ.)

End channel grading

Concrete collar

1:1 8"

TYPICAL SECTION

CHANNEL GRADING

4" depth and seed

Place topsoil, .5

6' bankfull width

8'

+402

NOTE:

FOOTNOTE:

DETAILS

RIPRAP HEADWALL

Sl op e

PIPE BEVEL DETAIL

Sl op e

SKEW ANGLE DIAGRAM

c e n te r li n e

R o a d w a y

Cu lv er t ce nt er lin e

BOP

EOP

(DIAMETER OR SPAN GREATER OR EQUAL TO 48-INCHES)

(DIAMETER OR SPAN LESS THAN 48-INCHES)

.2

D o r R

.2

D o r R o r R is e

R

D ia m e te r

D o r R is e

R

D ia m e te r

D

W

Sl op e

FRONT VIEW SIDE VIEW

[2

24" shown in the plans

Streambed material where shown in the plans

Streambed material where

V a ri a b le R is e

W2

Variable W2

V a ri a b le R is e

Placed riprap, class 3

Placed riprap, class 3

[3

" m in geotextile, class 1, type C

Separation and stabilization

Manufacturer's standards

0.25 D or R or per the

Optional

Skew

N e ig h o r n

/2

/2

C h e c k e d b y

D e s ig n e d b y

G.11

STATE PROJECT

NUMBER

SHEET

In t_ ft m y f il e s \p w p r o d u c ti o n

\d

\m t-a e z .d g n

AK FWS KNA 74525(1)

:5

A u g u s t beneath and at all sides of placed riprap.

Place earthwork geotextile between riprap and existing ground, Earthwork geotextile, type II-C is subsidiary to 251.

Contractor to field verify all invert elevations, prior to installation.

3.

2.

1.

shown on site specific details, whichever is greater.

Construct riprap end treatment to a thickness of 36-inches or as[3]

Riprap end treatment slope to match roadway embankment slope.[2]

Bevel to match roadway embankment.[1]

RIPRAP END TREATMENT

[1]

[1]

V

B e v a

N e ig h o

/2

/2

C h e c k e d b y

D e s ig n e d b y

G.12

STATE PROJECT

NUMBER

SHEET

In t_ ft m y f il e s \p w p r o d u c ti o n

\d

\m t-a e z .d g n

AK FWS KNA 74525(1)

:5

A u g u s t

SECTION VIEW

ANCHOR BOLT DETAIL

1.5

3'-0"

TYPICAL SECTION

THRU COLLAR

CONCRETE COLLAR

ISOMETRIC VIEW

3'-0"

3'

Sp an

3'

LC

Culvert crown

2' min. lap splice

#4 Reinf (6 total)

Culvert invert galvanized " Dia.4 bolt design - 4" hook

Acceptable anchorStructural plate pipe

18" o.c. See detail " Anchor bolt @4

#4

#4 stirrups m in

2' min. lap splice

#4 Reinf (6 total)

6" min.

To bedrock or 3' max.

To bedrock or 3' max.

COLLAR DETAILS

REINFORCED CONCRETE

LARGE CULVERT

SECTION A-A

PLAN

NOTE:

FOOTNOTE:

3.

2.

1.

Pipe arch culvert

W

Streambed sediment

Streambed cobble

Pipe arch culvert wall

Box culvert wall

Stagger in-channel fish passage boulders within the culvert span.

streambed cobble, and bank stone gradations.

See special contract requirements for streambed sediment, Mix streambed cobbles evenly throughout streambed sediment.

Channel flowline

Streambed sedimentRound pipe culvert wall Streambed top

Round culvert

Culvert wall

LC

Flow

BB

A where specified on plan

Sediment retention sill on plan where specified

Rock weir culvert boulder within

Fish passage where specified on plan

Sediment retention sill culvert boulder within

Fish passage

NO SCALE

Streambed Material.

Infill informational quantities are incidental to ITEM 64704-1000 [4] dimension.

smallest 4 3 Embed fish passage boulders within active channel [3] sediment where listed in the infill quantities table.

Construct well defined banks with bank stone and streambed[2] parabolic shape.

Slope streambed aggregate towards flowline to ensure[1]

[1]Channel flowline

[2]Bank stone

[2]Bank stone

TREATMENT

STREAM CULVERT

SIMULATED

A Flow

SECTION B-B

36" min.

Streambed cobble

Culvert outlet where specified on plan

Sediment retention sill

[3]within culvert

Fish passage boulder

Streambed sediment plan sheet or Length on

LC

specified on plan

Rock weir where outlet

Culvert

LOCATION

(FT)

X

(CUYD)

COBBLE

STREAMBED

(CUYD)

SEDIMENT

STREAMBED

(CUYD)

STONE

BANK

GRADATION

COBBLE

STREAMBED

(FT)

W

MITIGATION

FISH PASSAGE BOULDER

(IN)

DIA. NO.

[4]STREAMBED MATERIAL

TOTAL

.B e v

N e ig h o

/2

/2

C h e c k e d b y

D e s ig n e d b y

G.13

STATE PROJECT

NUMBER

SHEET

In t_ ft m y f il e s \p w p r o d u c ti o n

\d

\m t-a e w

.d g n

AK FWS KNA 74525(1)

:4

A u g u s t

SUCKER CREEK NA 16 24 4

UNNAMED TRIBUTARY NA 3 24 7

RAINBOW LAKE NA 6 18 5

C

D

B

(FT)

BD

1.5

3% (typ.)

Slope

295 295 39

B D

W

X (typ.)

B u ri a l d e p thd e p th

B u ri a l

X (typ.)

match rock weir spacing

Stagger fish boulders each side and

B

/3

Flow

F lo wA

A

(in)

DIAMETER

FOOTER ROCK

TOP ROCK AND

(no.)

QUANTITY

ROCK WEIR

MITIGATION

ROCK WEIR

(ft)

B

(ft)

[5] Z

(ft)

W

LOCATION

ELEVATION

PLAN

SECTION A-A

DETAIL

ROCK WEIR

NO SCALE

FOOTNOTE:

[4] [3]Footer rock

Z

D o w n s tr e a m f r o m c o n tr o l)

Top rock

Bottom of channel

Bottom of channel

[4] [3]Footer rock high water level

Ordinary normal low flow

Edge of water

Control point

6[3] [2]Top rock streambed material elevation or top of

Original streambed

[4] [3]Footer rock

[3]Top rock water level

Ordinary high

BWB

B W3

W 3

W3

B

W3

B e v

N e ig h o

/2

/2

C h e c k e d b y

D e s ig n e d b y

G.14

STATE PROJECT

NUMBER

SHEET

In t_ ft m y f il e s \p w p r o d u c ti o n \d

\m t-a e y .d g n

AK FWS KNA 74525(1)

:5

A u g u s t

SUCKER CREEK 16 1.75 6 4

UNNAMED TRIBUTARY 3 3 1.5 7

RAINBOW LAKE 6 1.5 3 5

Align footer rocks flush against bed retention sills inside culvert. [5] and stable foundation for the top rocks.

Place footer rocks close together to create a tightly packed[4] streambed material.

Fill voids in top rock and footer rock with specified[3]

Space top rocks in center 1/3 only.[2]

Orient top rocks to deflect water towards center of stream.[1]

[2] [1] [2] [1]

[2]

[2]

[2] [2] [2]

[2]

VAP

Existing ground

Roadway centerline

2000 50 100 15050100150200250300

Rainbow Lake

Section 703. — AGGREGATE

703.18 Furnished Streambed Material. (Added Subsection).

Streambed material consists of streambed sediment and streambed cobbles (class A, B, C, or D as specified on the plans) with volumes of each specified on the plans. Provide a uniform mixture.

Furnish material consisting of hard, durable, free from seams, cracks, and other defects conforming to the following:

(a) Durability index, AASHTO T 210

(1) Coarse aggregate 35 min.

(2) Fine aggregate 35 min.

(b) Apparent specific gravity, AASHTO T 85 2.55 min.

(c) Los Angles abrasion, AASHTO T 96 50% max.

(d) Gradation, Streambed Sediment. Furnish material meeting the gradation requirements of Table 703-13. Conserve round or sub-round material from the culvert and roadway excavation meeting the requirements of Table 703-13 to use as streambed sediment.

Table 703-13 Streambed Sediment Gradation

Sieve Size

Percent by Weight Passing Designated Sieve

(AASHTO T 27 and T 11)

6 inch 100

4 inch 75 – 85

3 inch 65 – 75

1 ½ inch 50 – 60

3/4 inch 35 – 45

No. 4(1) 15 – 25

No. 10 15 min.

(1) No more than 0.2 percent woody debris retained.

(e) Gradation, Streambed Cobbles. Furnish material meeting the requirements of Table 703-14. Conserve round or sub-round material from the roadway excavation meeting the requirements of Table 703-14 to use as streambed cobbles.

Table 703-14 Streambed Cobbles Gradation(1)

Nominal Size

Percent less than the nominal size Class

A B C D 28" 100 20” 65-75 14" 100 35-45 12" 100 85-95 30-40 8" 65-75 45-55 10-20 6" 45-55 30-40 4" 100 35-45 20-30 0-10 3" 30-40 15-25 2"

1 ½" 35-45 0-10 0-10 ¾" 10-15

(1) Grading of the cobbles will be by visual inspection of material before it is placed, and if directed by the CO, by placing material on a flat surface and sorting and measuring a sampling of the cobbles.

Note: Approximate size can be determined by taking the average dimension of the three axes of the rock; length, width, and thickness by use of the following calculation:

𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿ℎ + 𝑊𝑊𝑊𝑊𝑊𝑊𝐿𝐿ℎ + 𝑇𝑇ℎ𝑊𝑊𝑖𝑖𝑖𝑖𝐿𝐿𝐿𝐿𝑖𝑖𝑖𝑖

= 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝑊𝑊𝐴𝐴𝐴𝐴𝐿𝐿𝐿𝐿 𝑆𝑆𝑊𝑊𝑆𝑆𝐿𝐿

Project:

Location/Stream:

New Stream Channel Design (Culvert, Rock Ramp)

FINE 50%

Using Corps of Engineers Equations - FHWA Circular on Development in the River System - Page 6.25. COARSE 50% FHWA NHI 01-004; River Engineering for Highway Encroachments, 2001 http://www.fhwa.dot.gov/engineering/hydraulics/library_arc.cfm?pub_number=8&id=20

YELLOW ARE INPUTS

Safety Factor 1.5 Stability Coefficient for Incipient Failure 0.36 (0.36 round rock, 0.3 angular rock) Vertical Velocity Distribution Coeff 1.00 (1.0 for straight channels) Blanket Thickness Coeff 1 (1xD100 or 1.5 or D50 max, whichever is greater) Local depth of flow 1.8 ft for 100 year event Unit Weight of water 62.4 lb/ft^3 assumed Unit weight of rock 165 lb/ft^3 assumed Local depth-average velocity 5.6 ft/s from 100-year event avg. velocity in pipe Side Slope correction factor 1 Gravitational Acceleration 32.2 ft/s^2 D85/D15 5.2 (1.7-5.2) D50/D30 2 Note: This method is based on the minimum D30 size Riprap Design Method - Selecting Proper Gradation, Page 131.

Design Hydrology and Sedimentology for Small Catchments, Haan, Barfield and Hayes, 1981.

D15 0.2 ft 3.0 inches D30 0.2 ft 3.0 inches D50 0.4 ft 6.0 inches D85 0.7 ft 9.0 inches

D100 0.8 ft 11.0 inches

Using D50 size, used FHWA circular for Rip Rap design to spec out D100, D85 and D15.

D100 = 2.0D50

Fuller-Thompson Estimating for Maximum Density: D100 (inches) 11.0 Method Adapted from US Forest Service Stream Simulation Guidelines D30 3.0 Stability (D30):

D30 Req'd 3.0

YELLOW ARE INPUTS COARSE FINES

Custom Fine Aggreg. Combined %F-T EQN Check Coarse Material Design -D30 Required p RELATIVE % = 0.50 0.50 1.0000 Riprap D30 Riprap Req 3.0

Size (inches) Sieve Size % Passing % Passing % Passing % Passing % Passing D30 Size = 3.0 48 48 in 1.00 1.00 100% 209% 100% No OK 44 44 in 1.00 1.00 100% 200% 100% No 42 42 in 1.00 1.00 100% 195% 100% No 36 36 in 1.00 1.00 100% 181% 100% No 30 30 in 1.00 1.00 100% 165% 100% No 20 20 in 1.00 1.00 100% 135% 100% No 14 14 in 1.00 1.00 100% 113% 100% No 12 12 in 1.00 1.00 100% 104% 100% No 8 8 in 0.70 1.00 85% 85% 70% No 6 6 in 0.50 1.00 75% 74% 50% No 4 4 in 0.40 0.80 60% 60% 40% No 3 3 in 0.30 0.70 50% 52% 30% 3.00

1.5 1.5 in 0.15 0.55 35% 37% 15% 1.50

0.75 0.75 in 0.10 0.40 25% 26% 10% 0.75

0.187 #4 0.00 0.20 10% 13% 0% 0.19

0.0787 #10 Sand 0.00 0.15 8% 8% 0% 0.08

Gradation values should be within +/-5% of this gradation (Rice) AND we need to have at least 5% sand size (#10) or smaller (Forest Service) in the combined gradation

DATA for Graph & Fuller-Thomson Eqn Size (in) Combined % pa F-T equation

48.000 100% 209%

44.000 100% 200%

42.000 100% 195%

36.000 100% 181%

30.000 100% 165%

20.000 100% 135%

14.000 100% 113%

12.000 100% 104%

8.000 85% 85%

6.000 75% 74%

4.000 60% 60%

3.000 50% 52%

1.500 35% 37%

0.750 25% 26%

0.187 10% 13%

0.079 8% 8%

OK

MATERIAL PROPORTIONS

AK FWS Kenai 74525(1) - Swan Lake / Swanson Rive

Rainbow Lake Culvert

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.010 0.100 1.000 10.000 100.000

P as si n g

Particle Size

Design

Fuller‐Thomson

YELLOW ARE INPUTS

Desired tolerance (+/-): 5%

SIEVE % PASSING

12 in 1.00 8 in 1.00 6 in 1.00 4 in 0.75 to 0.85 3 in 0.65 to 0.75

1.5 in 0.5 to 0.6

0.75 in 0.35 to 0.45

#4 0.15 to 0.25 #10 Sand 0.15 min

Desired tolerance (+/-): 5%

SIZE % PASSING

48 in 1.00 44 in 1.00 42 in 1.00 36 in 1.00 30 in 1.00 20 in 1.00 14 in 1.00 12 in 1.00 8 in 0.65 to 0.75 6 in 0.45 to 0.55 4 in 0.35 to 0.45

3 in 0.3 to 0.4

TABLE 1

FINE MATERIAL

TABLE 2

COARSE MATERIAL

Rainbow Semi-log Gradation Plot

Roadway Data for Crossing: Rainbow Lake

Streambed Material Sizing Analyzer_Rainbow Creek

Roadway Data for Crossing: Rainbow Lake

7-HY8Report_Rainbow Lake

Streambed Material Sizing Analyzer_Rainbow Creek