Appendix_F_-_Final_Fish_Passage_Recommendation_January_2005.pdf

Appendix F Fish Passage Recommendation

(January 2005)

An employee-owned company

5500 Greenwood Plaza, Suite 150, Greenwood Village, Colorado 80111 Telephone: (303) 221-7275 Fax: (303) 221-7276

MEMORANDUM

TO: Ken Burns, P.E.

FROM: Jeff Sickles, P.E.

DATE: February 1, 2005

SUBJECT: Beartooth Highway Fish Passage at Proposed Replacement Culvert (Sta. 47+000)

Executive Summary

During one of the field review meetings for the proposed Beartooth Highway Improvements, Wyoming Forest Highway Project WY HPP 4-1(4), the presence of fish in the drainageway crossing under the highway was identified near proposed roadway station 47+000. This drainageway is a tributary to Little Bear Creek. As it presently exists, fish travel through the existing double 36-inch CMP culverts. A design has been developed to provide for a new and improved passage structure. Based on conversations in the field, evaluations of various alternatives and recommendations from numerous technical documents, a new buried bottom culvert has been proposed at the crossing. It is recommended that a 2900 mm x 1960 mm corrugated metal arch culvert pipe be used for the proposed culvert crossing. This structure will convey the 50-year design flow while meeting the maximum allowable headwater to depth ratio and will also allow for the culvert bottom to be partially buried providing improved fish passage conditions. The existing stone masonry will be salvaged and a headwall will be designed at the upstream end of the new culvert. The pipe will be installed to maintain the existing channel grade. No significant headcuts or drops were observed in the field, which might require additional fish passage measures. The culvert grade will be designed so that the maximum velocity through the culvert for the 2-year event is less than 1.22 mps (4.0 fps). This is the recommended velocity for adult trout (<150 mm) for culvert lengths between 30.5 m and 61 m (100 – 200 feet). A memorandum providing additional discussion and supporting hydraulic calculations is provided in the Appendix of this report.

Recommendations for the fish passage structure are based on the document entitled Fish Passage Design at Road Culverts produced by the Washington Department of Fish and Wildlife (1999). Final design of the passage will consider recommendations from other organizations including the U.S. Department of Fish and Wildlife (USFS).

Existing Conditions

The existing structure consists of two 36-inch corrugated metal pipes with a stone masonry headwall at the upstream end of the structure. No end treatment is provided at the downstream end of the culvert.

The pipe is in relatively good condition and has no sign of structural failure. The pipe is clean with very little sediment material residing inside the pipe. The pipe was observed at both low flow (late summer) and high flow (early summer) conditions. Fish were traveling freely through the pipe under low flow conditions. Velocities appeared relatively high for high flow conditions, however, the presence of fish was noted in the channel just downstream of the pipe outfall. Photos of the site are provided below.

Beartooth Highway Fish Passage

February 1, 2005

Hydrology

Design flows for this location were calculated using both the Rational Method and Regression Methods.

These two methodologies were used for hydraulic capacity (Rational Method) and fish passage design (Regression). This allowed for a worst-case design for hydraulic capacity while providing a more realistic annual flow estimate for fish passage. The basin area draining to the site is approximately 0.5 square miles (320 acres). Base flows in the channel are due to snowmelt while a large rainfall event could potentially cause the types of flood flows estimated by the Rational Method.

Table 1 : Design Point Rainfalls

Design Frequency

Rational

(cms) Regression

(cms) 2-year 2.73 0.28 10-year 5.268 0.58 50-year 7.641 0.89

Hydraulics

Culvert hydraulics were evaluated using Haestad’s CulvertMasterTM. A conceptual analysis of the hydraulics using the publicly available FishXing software was also performed. It is assumed that a low tailwater basin will be constructed at the outlet of the pipe with a downstream sill that is 75mm higher than the downstream invert of the pipe. This stilling basin will provide a pooling area for fish to reside in prior to traveling up the culvert and will also provide a backwater into the culvert, thereby reducing the outfall velocity. A typical low tailwater basin design is shown in figure 1.

The proposed pipe is 40 m long with a slope of 1.5%. The estimated 2-year velocity through the pipe for a flowrate of 0.28 cms is approximately 0.90 mps. This is below the maximum velocity of 1.22 mps.

The maximum velocity is exceeded flow flows in excess of 0.56 cms which is just slightly below the predicted 10-year snowmelt event.

Headwall at upstream end of existing structure. Channel downstream of existing structure.

Figure 1 : Typical Low Tailwater Basin

Design Discussion and Alternative Analysis

There were three crossing options considered for this structure.

1. An oversized culvert structure with a portion of the culvert buried below channel grade. This would allow for a “natural” channel bottom and would maintain the gradient in the stream.

2. A three-sided culvert structure with footings. This structure would maintain a “natural” bottom and stream grade.

3. A bridge structure that would span the stream.

A comparison of the alternatives is presented in Table 2. Issues evaluated include applicability to fish passage, cost and construction concerns.

Table 2 : Alternative Comparison

Alternative Fish Passage Cost Construction Oversized culvert with buried bottom

Provides for natural channel bottom.

Acceptable alternative per fish passage guidelines.

Least expensive option. Standard culvert installation. Rapid construction.

Three-sided culvert with footings

Provides for natural channel bottom.

Acceptable alternative per fish passage guidelines.

Slightly more expensive than simple culvert due to footing construction.

Requires formwork, overexcavation for footings and longer duration of construction.

Bridge Structure Provides for natural channel bottom.

Acceptable alternative per fish passage guidelines.

Most expensive. Longest duration of construction.

All of the alternatives are acceptable designs for fish passage. During an onsite meeting with Forest Service biologists it was indicated that a three-sided culvert was desired and ideally this structure would be located on an alignment along the existing channel. This structure would essentially span the stream bottom. Issues associated with this type of structure include local and long term scour susceptibility. In order to reduce local scour, riprap would be installed through the culvert to protect the structure’s foundation. This material would likely fill in with sand and would generally conform to the rock material that presently exists in the channel. Long term maintenance of a three-sided structure could be significant if local scour occurs inside of the structure itself where access is limited.

A fully enclosed structure with a buried bottom eliminates the local scour issue inside of the pipe. Inlet and outlet scour can be handled by riprap at the upstream end and a stilling basin on the downstream end of the structure, which will also protect from long term scour downstream. Both of these options provide natural stream bottoms for the long term.

Constructability

Constructability was a major consideration in a recommended alternative. As previously mentioned a three-sided culvert located on an alignment along the existing channel was the preferred alternative. The construction of such a structure would require a footing extending to a depth of four feet below ground.

Typical excavation for such a foundation would be extensive and would cause significant disturbances in the vicinity of the project area. This foundation would also be relatively expensive. The construction of an oversized, buried-bottom, culvert in an off alignment location will require less disturbance, overexcavation and will be a cheaper cost alternative.

Cost

For comparison purposes it was assumed that the fully enclosed arch and the 3 sided CMP arch would be approximately the same. The only additional costs for the 3-sided structure would be the foundation (concrete) and excavation and backfill costs and riprap through the structure to provide for scour protection. Table 3 presents a preliminary cost analysis for the additional items. It is estimated that a 3-sided structure will increase the cost of the structure by over $55,000.

Table 3 : Foundation Costs

Item

Quantity Unit Unit Cost Total Cost

Concrete (includes steel) 44 cu. m $600/cu. m $26,400 Structural Excavation 245 cu. m $50/cu. m $12,250 Structural Backfill 245 cu. m $50/cu. m $12,250 Riprap 54 cu. m $130/cu. m $7,020 Total $57,920

Recommended Design

Based on a comparison of key issues the recommended design will consist of an oversized culvert which will be partially buried (<40% of the height below the channel grade). This recommendation is primarily based on cost as well as the period of time needed to construct the passage. As was discussed in the field, the replacement structure will be built offline from the stream in order to minimize disturbances during construction. Once the structure is installed, minor realignment of the stream will occur to direct water through the new culvert. The width of the culvert will be based on the bank full depth of the channel in the vicinity of the new crossing using the following equation:

Wculvert bed = 1.2Wch + 2 (in feet)

Where Wch is the width of the channel bed.

A channel with a 1.5m (5 foot) bottom and 2:1 side slopes was estimated based on field observations of the channel. A first estimate for the culvert width based on the above equation would be 2400 mm (8 feet).

In cases where the channel bed is poorly defined the recommended width should correspond to approximately the 2-year recurrence interval flood. The estimated top width for the 2-year flow based on hydraulic calculations is 2.31 mm (8.0 feet). Therefore, the recommended culvert width could be between 2400 mm and 3300 mm.

Hydraulic sizing of a culvert able to adequately pass the 50-year flow without exceeding the maximum headwater indicates a 2130 mm x 1550 mm arch for the crossing. This is slightly smaller in width than the 2400 mm recommended and would not allow for a partial burying of the culvert bottom. To allow for the culvert bottom to be partially buried it is recommended that a 2900 mm x 1960 mm arch culvert be used. Figure 2 shows a section reflecting the channel, the pipe required to pass the 50-year flow per the design criteria and the recommended pipe that provides for fish passage.

Figure 2 : Culvert Cross Section cc: Bert McCauley, FHWA Jennifer Corwin, FHWA

Mark Meng, FHWA Kristin Lang, PBS&J Dean Friesen, PBS&J Richard Trenholme, ERO

Liz Payson, ERO Aleta Powers, ERO Mark Holdeman, HLA