Water Stewardship Information Sources
| Citation | Kerr Wood Leidal Associates Limited. 2012. Englishman River Water Balance - Preliminary Hydrologic Assessment. Technical Memorandum produced for BC Conservation Foundation. |
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| Organization | BCCF |
| URL | http://www.fraserbasin.bc.ca/_Library/CCAQ_BCRAC/bcrac_englishman_river_water_balance_2d.pdf |
| Abstract/Description or Keywords | The Englishman River is an important salmon-producing stream on the east coast of Vancouver Island. The watershed has all species of salmon, including steelhead and is designated as a sensitive stream by the BC government under the Fish Protection Act. However, the fish stocks on the river have generally been in-decline since the mid-1980s. A Recovery Plan for the river was prepared by LGL Ltd. in 2001. This study outlined the existing (2001) baseline conditions of stream habitat and fish health, identified the key factors influencing recovery of the stream and developed a goals and objectives for recovery. The LGL study identified that one of the factors influencing recovery is low river discharges during the dry summer months. It is necessary to provide short term maintenance flow of 1.44 m3 /s or 10% of mean annual discharge (MAD) in order to sustain healthy stream habitat during the dry summer period. Currently, the provisional operational rule for the Arrowsmith Lake Dam, operated by the Arrowsmith Water Service (AWS) requires that sufficient flow be released from the dam to maintain 1.6 m3 /s in the river. This flow is slightly higher than the minimum short-term maintenance flow in order to account for municipal water demand at the point of diversion, downstream of Highway 19a. However, during the past seven years the minimum 1.6 m3 /s has not been sustained for the entire summer low-flow period. For the period of available records during operation of the AWS reservoir (2000 to 2006), the flow in the river fell below the 1.6 m3 /s threshold for 47 days on average and below the 1.44 m3 /s threshold 33 days on average (see Table 1). The lowest recorded flow during the period is 0.67 m3 /s in 2000. These shortfalls may be due to constraints of the existing rule curve, which require outflow from the reservoir to equal inflows up to the beginning of June. However, other factors such as changes in land-use, increased water demand and changes in climate may also be influencing the water available during the low-flow season. A hydrological assessment of the Englishman River was carried out as part of the Englishman River Water Intake Study for the Arrowsmith Water Service (AWS) in 2010 (KWL & AE, 2010). This assessment reviewed the storage capcity of Arrowsmith Lake to support both current and future water supply demand and conservation flows. The assessment reviewed if minmum conservation flows could be maintained at current levels along the full length of the river with consideration that the proposed municipal water supply intake was moved upstream of the current location. The AWS study concluded that: 1. the existing Arrowsmith Lake Dam has sufficient storage capacity and adequate minimum discharge outlet capacity to maintain a minimum flow of 1.2 m3 /s downstream of the proposed water supply intake location under current 1:10-year drought conditions and municipal water demand conditions; 2. Arrowsmith Lake has sufficient storage to maintain minimum flow of 1.2 m3 /s under future 2050s climate and municipal water demand conditions but that the outlet structure does not have sufficient capacity to maintain this flow when water levels in the reservoir drop below El. 881.5 m, which is equivalent to about 27% of full storage in the reservoir; 3. that both the storage and outlet capacity at Arrowsmith Lake are not be sufficient to maintain current minimum flows of 1.6 m3/s recommended in the provisional operating rules under both current and future climate and demand conditions; 3. that increasing storage at the Arrowsmith Lake Reservoir would not increase the due to the limited inflow to the reservoir from the relatively small watershed area above the lake of 5 km2 or 1.5% of the total Englishman River watershed area. |
| Information Type | Report |
| Regional Watershed | Vancouver Island South |
| Sub-watershed if known | |
| Aquifer # | |
| Comments | |
| Project status | complete |
| Contact Name | Craig Sutherland |
| Contact Email |