Ministry of Environment
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Report: Water Use and Management in the Koksilah River Watershed

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This report quantifies present surface water and groundwater demand from different water use sectors, and historical development of water use in the Koksilah River watershed, Vancouver Island. Provincial government actions taken in the summer of 2017, 2018, and 2019, in response to low flow conditions threatening the survival of aquatic life are discussed, including development of a groundwater curtailment model.

Date Published:  Dec 2020

Report ID:  59126

Audience:  Government and Public

The Koksilah River on southeastern Vancouver Island is prone to low flows during the summer dry season, potentially affecting habitat suitability and the survival of aquatic life including salmonid species. Enactment of B.C.s Water Sustainability Act (WSA) in February 2016 provides new tools for integrating surface and groundwater management. Along with licensing of non-domestic groundwater use, the Act enables protection of environmental flow needs, requires consideration of potential hydraulic connection between groundwater and surface water sources, and contains tools to regulate water use during times of scarcity to protect fish and aquatic life, and to protect the rights of senior rights holders. This report examines some of the questions involved in implementation of the Act in the Koksilah watershed including quantification of groundwater demand after years of unregulated groundwater development, and identification of where and how groundwater use may be influencing surface water flows. Although a restriction on issuing surface water licences on the Koksilah River and tributaries was imposed in 1980, total water demand in the watershed increased since that time due to unregulated groundwater development (pre-2016). Groundwater flux to the Koksilah River is understood to be an important influence on environmental flow needs, providing base flow and maintaining instream conditions, such as cooler water temperatures, that benefit aquatic species. In recent years, flows in the Koksilah River have diminished to levels where the healthy condition of aquatic habitats and the survival of fish populations are likely threatened. A groundwater curtailment model was developed to identify groundwater use that, if stopped temporarily, would help improve instream flows should they reach a critical point where significant harm to survival of aquatic species was likely. In August 2019, a Temporary Protection Order (TPO) under WSA section 88 was issued that required specified users to curtail groundwater and surface water use. Monitoring results demonstrated that the TPO likely resulted in an increase in streamflow compared to historical conditions and anticipated seasonal streamflow recession in the absence of rainfall. Recommendations are provided for future monitoring, technical assessment and planning, needed to address equitable water resource distribution and protection of Indigenous water rights, while maintaining minimum streamflow for the protection of aquatic life. This case study will be of interest to the public, researchers and water managers in this region and in other areas of B.C. facing similar water resource challenges.

Report Type
  Biogeoclimatic Zone - CDF Coastal Douglas-fir Zone
  Region - Vancouver Island
  Fish and Fish Habitat - Impact Assessment
  Fish and Fish Habitat - Management
  Watershed Groups - 920 - Vancouver Island (East) Rivers
  Water Information - Groundwater
  Water Information - Hydrometric / Hydrology
  Water Information - Water Management
  Water Information - Watershed Assessment Studies
  Water Information - Water Supply

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