Fawn Creek Culverts Prevent Fish Passage

To-day, July 10, 2000, appeals signed by organizations and individuals resident in the area of the culverts where Beaver Creek Road crosses Fawn Creek, were sent to the Ministry of Highways, DFO (federal Department of Fisheries and Oceans) and Gerard Janssen, Member of the B.C. Legislature, asking for repairs to be done.
After the B.C. Ministry of Highways put in these culverts 35 years ago, the force of the water eroded the pool at the culvert outlets making it impossible for fish to ascend to their traditional spawning and rearing habitats up-stream. 
For over a year, the Hal Creek Watershed Protection Society has been corresponding with DFO and the Ministry of Highways trying to get this situation remedied. DFO agrees that the culverts need to be fixed but Highways says if DFO wants it fixed, they should pay for it.
The organizations who have signed the appeals asking for action before the coho run this fall are: Nuu-chah-nulth Tribal Council, Huupacasath First Nation, Regional Aquatic Management Society, Alberni Environmental Coalition, Council of Canadians, Alberni Valley Enhancement Association, Area/G Troll Fishing Association, Alberni Salmon Enhancement Society, Alberni Sport Fish Advisory Committee and the Alberni District Sportsman’s Association. For more detailed information on the culverts, we are providing the following excerpts from a publication of the Hall Creek and Mt. Hal Watershed Protection Society, A Hydrological Analysis of the Hal Creek Watershed, July 1999, by Northwest Hydraulic Consultants (#2-40 Gostick Place, North Vancouver BC V7M 3G2).

Excerpts from NHC Report:
 
5. THE CULVERTS AT THE BEAVER CREEK ROAD
 
5.1 Site Visit
 
The culverts were visited on June 15, 1999, during the snow-melt freshnet. Depths of fill and culvert dimensions were estimated with a measuring tape when standing on the culverts. There are two culverts at the site: a 800-mm diameter corrugated metal pipe (CMP) that has been placed with its invert about 1.3 m below the top of the road and a 800-mm diameter concrete pipe placed with its invert about 6 m below the top of the road. During the site visit, the water was almost to the top of the concrete pipe, so its exact diameter could not be measured (Photo 13).
 
We observed erosion at both the outlet of the CMP in the road fill (Photo 14), and at the outlet of the concrete culvert where it plunges into compacted till (Photo 15). Rock protection does not appear to have been placed at either outlet; if it was placed, it has been eroded away. There is an extreme drop at the outlet of the lower culvert; however, its exact height could not be measured due to high water levels. Serensia [1999] states that the streambed is about 9 feet (2.7 m) lower than the outlet of the concrete culvert, with a 12-foot setback.
 
Erosion is occurring on the left bank at the culvert outlet. Above the erosion a house is situated 20 feet away [Dickey, 1999, pers comm.] from the 8-9 m (approx.) high slope that is eroding. Because of this situation, there is an urgent need for remedial works at the culvert.
 
We also observed erosion around the intake of the concrete culvert (Photo 13). This may indicate that water is seeping around the concrete culvert.
 
5.2 Hydrology and Hydraulics
 
The current design discharge standard for a permanent crossing of a fisheries stream is the 100-year return period flow, passed with water levels at the top of the culvert. Table 2 summarizes our peak flow estimates at this site with the 100-year instantaneous maximum estimated to be between 13 and 17 m3/s.
 
Our preliminary analysis indicates that the present culverts are not adequate to pass the 2-year instantaneous maximum, let alone the design flow, and that there would be water flowing over the road during the 2-year flood. These results are consistent with the local residents’ observation of the water overtopping the road. 
Velocities of water exiting the culverts during the 2-year peak flow are estimated to range from about 2.5 to 4.5 m/s.
 
5.3 Cause of Erosion
 
The erosion downstream of the culvert outlets is caused by the high velocities exiting from the lower culvert and the jet of water plunging from the CMP set high in the road fill. The wide scour hole below the culverts, in the resistant till, suggests that back eddies formed on the margin of the jet have contributed to erosion at the culvert exit (Photo 15).
 
In the absence of sediment supply from upstream, the channel downstream from the culverts will continue to lower its bed until a limiting low slope is reached where material is no longer mobile, or until erosion resistant materials are uncovered. Channel widening downstream of the culverts may continue, even if bed lowering is reduced or stopped, from failure of the over-steepened till sediments.
 
5.4 Required Culvert Sizes
 
Our preliminary investigation shows that the following structures would pass the estimated design flood for Hal Creek at the Beaver Creek Road: 

• A box culvert 3 m by 1.5 m,
• An arch culvert 3.6 m by 2.4 m,
• A circular CMP with 2.8 m diameter, or
• A bridge with similar dimensions. 

In selecting the dimensions of the above structures, we assumed that they are not to surcharge, and that the ratio of headwater depth to culvert diameter (Hw/D) is less than or equal to 1. The culvert or bridge crossing design would also be required to meet the standards in the “Stream Crossing Guidebook for Fish Streams”, which may result in a larger structure than quoted above. 
Detailed survey and design would be required for any replacement structure as the steep drop downstream of the existing culverts will require instream works to ensure fish passage.
 
8. DISCUSSION AND CONCLUSIONS
 
8.1 Erosion on Hal Creek Fan
 
The erosion along Hal Creek, on its fan, began prior to harvesting of the MOF block. It is our view that the harvesting, particularly removal if riparian trees, and subsequent remedial activities have aggravated the erosion and increased the downstream transport of gravel and sand. Deepening Hal Creek, which effectively channelized it, increased its capacity so that most flow stays in the channel, aggravating erosion. Gravel mining below the marine clay canyon did not initiate nor exacerbate the erosion on Hal Creek fan.
 
Check dams were installed to store gravel and maintain the excavated bed profile. These dams have functioned to store sediment and aggrade the bed. However, they have partly failed, likely because a scour apron was not installed, and they now pose a threat of further failure during an extreme flood. Maintenance of the dams is required. They should either be re-built with an apron, or the stored sediment removed, and the channel bed and banks armoured with the coarse rock from the check dams. Detailed engineering design is recommended for either option.
 
8.2 Beaver Creek Road Culverts
 
Our preliminary assessment indicates that the culverts are too small to pass the 2-year instantaneous maximum flow. Note that there is considerable uncertainty about the magnitude of the peak flows in Hal Creek at Beaver Creek Road.
 
The erosion downstream of culvert outlets is caused by high velocity water, containing little or no sediment, discharging from the culverts. Channel deepening may continue until downstream slopes are too low for sediment transport, or until resistant materials are exposed. Channel widening may continue, even if bed lowering is reduced or stopped, from failure of the over-steepened till sediments. As this erosion is occurring beside a private residence, and the house is approximately 20 feet away form the edge of the erosion [Dickey, 1999 pers comm.], continued erosion may affect their house; there is therefore an urgent need for remedial works at the outlet. The culverts do not appear to be passable by upstream migrating salmon or resident fish.
 
A variety of structures could be installed to pass the design flow, such as a box culvert, an arch culvert, a circular CMP or a bridge. Design for these structures should meet the standards in the “Stream Crossing Guidebook for Fish Streams”, prepared under the Forest Practices Code. Note that the deep scour hole and degraded channel downstream of the existing culverts provides a difficult design problem for fish passage. 
 
9. FURTHER STEPS
 
9.2 Hal Creek Culvert
 
The existing culverts do not appear to be passable by upstream migrating salmon or resident fish and are not adequate to pass the design flood. We recommend that the Ministry of Transportation and Highways assess their existing culverts and replace them with suitable structures. The threat of erosion to private property on the left bank at the outlet adds urgency to the need for remedial measures.