USDA Forest Service-Prince William Sound Zone

Goose Meadows Culvert Replacement Monitoring Report

Report Date: November 7, 2017 Author: Luca Adelfio1

1 Luca Adelfio is an Interdisciplinary Hydrologist/Fish Biologist, U.S. Department of Agriculture, Forest Service, Chugach National Forest, Prince William Sound Zone, P.O. Box 280 Cordova, Alaska 99574. He can be reached by e-mail- ladelfio@fs.fed.us.

Photo caption: USFS Fisheries Technician R. Ertz measures velocity at the original culvert outlet with an Acoustic Doppler Current Profiler. Photo by L. Adelfio

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Introduction

Replacing culverts with “fish-friendly” designs developed with stream simulation techniques improves passage for aquatic and riparian organisms and increases conveyance of flood flows and debris, restoring ecological conditions and stream channel function, preventing road damage during floods, and reducing highway maintenance costs.

Although stream simulation techniques have been broadly applied throughout North America and the ecological benefits of fish-friendly culverts are well-documented, monitoring project sites before and after a new installation is valuable to: (1) ensure function, (2) improve implementation methods, and (3) document use by anadromous fish.

Monitoring is particularly important at high latitudes, where unique hydrologic and climatic conditions may complicate project design and implementation.

We monitored channel conditions and anadromous fish use before and after a fish-friendly culvert replacement project at Goose Meadows Creek, milepost 20 Copper River Highway on the Copper River Delta near Cordova, Alaska. Goose Meadows Creek provides high-quality spawning and rearing habitat for Coastal Cutthroat Trout (Oncorhynchus clarki) and Coho Salmon (O. kisutch). A velocity barrier through the original culvert blocked upstream passage of juvenile trout and salmon at moderate flows and adult trout and salmon at high flows. This report describes our assessment of the effectiveness of replacing the culvert with a fish-friendly design.

Materials and Methods

We measured channel profile and discharge and documented presence of spawning Coastal Cutthroat Trout and Coho Salmon in 2015, 2016, and 2017.

Pre-project surveying was performed by hydraulic engineering staff at Alaska Department of Transportation with a total station on May 5, 2015. The culvert was replaced in December, 2016. Post-project surveying was completed by USDA Forest Service personnel with a laser level and surveying tape on September 6, 2017. The survey data were applied in a steady flow model to compare maximum flow velocities at the downstream end of the original and the fish-friendly culverts using HEC-RAS v.5.0.3 software. Two discharges were selected for this analysis based on field measurements.

Discharge was measured by USDA Forest Service personnel using a handheld current meter at wade-able stages and an Acoustic Doppler Current Profiler at high water stages. Adult cutthroat trout migrate upstream to spawn in the spring, typically early May, so we modeled maximum velocity based on a discharge measurement taken on May 7, 2015. Adult Coho Salmon migrate upstream to spawn in the autumn, typically late August into September, so the second discharge selected was measured on August 26, 2016 during a high water event. The maximum flow velocity at the culvert outlet was measured at the same time discharge was quantified.

The presence of spawning Coastal Cutthroat Trout and Coho Salmon was assessed by walking along known spawning reaches upstream from the culvert location and looking for fish in the spring and in the fall.

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Results

Maximum Velocity Modeling We measured a discharge of 5 cubic feet per second and a maximum culvert flow velocity of 1 feet per second on May 7, 2015 and a discharge of 99 cubic feet per second and a maximum culvert flow velocity of 9.0 feet per second on August 26, 2016. The maximum velocities modeled by a steady flow model at these discharges were within 0.3 feet per second of the observed values. Our model indicated the fish-friendly culvert reduced maximum velocities by 71% when discharge was 99 cubic feet per second and by 80% when discharge was 5 cubic feet per second (Table 1).

Table 1. Maximum velocity of water flow at the outlet of the original culvert and the fish-friendly replacement culvert modeled at two discharges under steady-state flow assumptions.

Anadromous Fish Presence We observed Coastal Cutthroat Trout and Coho Salmon spawning upstream from the culvert before and after replacement, indicating that improving fish passage through this culvert will benefit juvenile salmonids by improving habitat connectivity.

Discussion

Flood flows through the original culvert were a barrier to adult Coho Salmon and Coastal Cutthroat Trout. Moderate water stages, a common occurrence in the coastal rain forest, were a barrier to juvenile salmonids and other aquatic organisms.

The new fish-friendly arch culvert has substrate in the bottom, adding roughness that will better enable juvenile salmonids, sculpin, and aquatic insects to travel through the culvert. The greater width of the new culvert will increase the volume of low velocity water along the walls of the structure, increasing the availability of quiet flow areas where aquatic organisms can travel and rest. Additionally, the maximum water velocities in the center of the fish-friendly culvert are considerably lower, greatly facilitating passage at high water stages.

The orientation of the fish-friendly culvert is skewed relative to the thalweg, a necessary engineering compromise since a longer culvert would have had increased long-term costs associated with bridge inspections. Due to the orientation, the fish-friendly culvert may continue to erode the downstream river left bank, erosion started by the original culvert. We will continue to monitor bank stability downstream from the culvert and we will restore this bank if natural revegetation does not occur. Additionally, we will periodically assess changes in channel profile

Modeled Measured Modeled Reduction99 8.7 9.0 2.5 71%5 1.2 1.0 0.2 80%

Discharge (ft3 s-1)

Original CulvertMax Velocity (ft s-1)

Fish-Friendly Culvert

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and particle size over time in and near the fish-friendly culvert, particularly after large storm events.

A new beaver dam downstream from the fish-friendly culvert is backwatering the culvert, facilitating aquatic organism passage. We did not consider this backwater in our modeling, so actual maximum velocities are likely even lower than our modeling suggests. Due to increased conveyance through the fish-friendly culvert, beaver activity in this reach can continue to occur without increasing maintenance costs. Beaver ponds are important habitat features for rearing Coho Salmon on the Copper River Delta.

Photo caption: The upstream end of the original culvert was fully submerged during high waters events, backing up water upstream from the road, impeding fish passage, and creating this "whirlpool" at the culvert inlet.