Water Stewardship Information Sources
| Citation | Worley Parsons. 2009. South Cowichan Water Plan Study: A preliminary assessment of water supply & needs with the south Cowichan region. Prepared for Cowichan Valley Regional District. |
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| Organization | Cowichan Valley Regional District |
| URL | http://cvrd.bc.ca/DocumentCenter/Home/View/7952 |
| Abstract/Description or Keywords | WorleyParsons and Westland Resource Group were jointly retained by the Cowichan Valley Regional District (CVRD) to undertake a preliminary water plan study of the South Cowichan region. This water plan study was designed to provide CVRD with the tools necessary to develop a water management framework for the region that will maintain its unique hydrological and ecological values while supporting appropriate kinds and scales of human activities. The region that forms the subject of this report (the Study Area) consists of CVRD’s Electoral Areas A and C in their entirety, and those parts of Electoral Areas B, D, and E that lie within the Shawnigan, Cowichan and Saanich Inlet watersheds. The Study Area covers 20,853 hectares of land, and is centred on latitude 48o 38’N and longitude 123o 36’W (UTM coordinates 5388132N 455163E, Zone 10). The main objectives of this project were as follows: To compile a comprehensive summary of existing technical information relating to the region’s current water resources and needs, including calculation of the area’s existing water balance using available data and evaluation of interactions between its key components; To estimate future population growth, land use patterns, and water supply / demand for the next 30 years using projections based on past trends, with emphasis on the identification of key issues that could potentially result in water shortages within the region; To evaluate the effects of existing government policies and regulations on water use within the region; and To develop a Terms of Reference for CVRD that will facilitate the development of a comprehensive Water Management Plan for the region that will ensure the South Cowichan region’s water supply is capable of meeting projected demand in a sustainable and ecologically sensitive fashion. At the request of CVRD, water resource data collection and evaluation focused on defining the occurrence, distribution, development, and usage of groundwater within the Study Area. The key findings of this study are presented below. Water Uses and Needs The three watersheds in the South Cowichan area each support a diverse range of land uses and ecological habitats; More than 17,000 people currently live in the South Cowichan communities of Cobble Hill, Mill Bay, Malahat, Shawnigan Lake Village, and Cowichan Bay, and are contained within 7,477 housing units. The Shawnigan watershed contains the greatest number of housing units (3,992), followed by the Cowichan watershed (2,680 units), and the Saanich Inlet watershed (805 units). Provincial government estimates suggest that the number of housing units in South Cowichan could grow by 28% to 9,500 by 2036. If residential developments now being planned are built, the number of units could potentially reach 13,700 by 2036. Depending on the extent of future development, the 2036 population could range from 22,000 to 32,000. It is important to recognize that global phenomena, such as climate change and economic fluctuations, increase the uncertainty associated with projections of future growth in the South Cowichan area; A variety of plans, regulations, and guidelines currently affects water and land use in the South Cowichan area. Ten provincial acts and four federal acts are relevant to water and watershed management in the Study Area, and community land use plans have been developed for all of its electoral areas. CVRD authority in water management is presently unclear since local governments’ abilities to implement and enforce water use policies within their jurisdictions are limited by the present water governance structure in British Columbia; Uncontrolled water use for farming, cattle rearing, wineries, and new land development projects in the South Cowichan area will place increasing pressure on its existing water resources. The present estimated water demand for all land uses use within the South Cowichan area is estimated at 26 million m3 /yr. By 2036, these demands may grow to 34 million m3 /yr. With active water conservation measures and urban densification, total water demand in 2036 could remain the same as today’s estimated consumption, as would the distribution of demand among future agricultural, residential, and other urban uses. Without conservation, the residential component could grow from 7 to 10 million m3 /yr, which highlights the importance of future land use decisions as part of a sound water management strategy; Agricultural activities account for a substantial proportion of current water use in the South Cowichan area (15 million m3 for agricultural use, compared to 7 million m3 for residential and 3 million m3 for “other” urban uses). Detailed information is not presently available concerning the amounts of water used by different agricultural activities. Based on the disproportionate use of water by agricultural activities within the Study Area, prudent water management planning should carefully consider the value of conservation measures to ensure that an adequate supply of water is available for the region’s other users, and should identify potential obstacles to attaining water use efficiencies; The South Cowichan area’s five First Nations reserves and major non-governmental water users (primarily educational institutions) constitute a relatively small component of its overall water use, although their demand volumes in the Shawnigan and Cowichan watersheds exceed commercial and industrial consumption. Water use on First Nations reserves is currently fairly limited, but may grow significantly as their respective residential community plans and commercial developments are implemented; The relative proportion of current groundwater to surface water use within the Study Area is not currently known with precision, since regional groundwater extraction rates are not monitored with the same accuracy as surface water diversion rates; The hydrology and patterns of water use in the South Cowichan area could change substantially by the conversion of existing forest land to urban uses. More information on the likelihood of these conversions will be needed as the water planning process proceeds. Specific estimates water supply demand to service new forest-urban land conversion developments should be undertaken, as well as projections regarding the extent of potential modifications to the surface water and groundwater hydrological regimes on the subject developments and their cumulative effects on downstream land parcels; and Many opportunities exist in the South Cowichan area for water conservation and demand reduction, although very little area-specific information on these topics is currently available. Future regional water planning should include the identification and implementation of such measures, which could be used to forecast future water use more accurately and determine the potential effects of urban growth on the area’s groundwater and surface water resources. Groundwater Government mapping has delineated 13 groundwater aquifers within the South Cowichan area. Surficial aquifers are mainly hosted by unconsolidated glaciofluvial and morainal sand and gravel deposits of the Vashon Drift and Capilano Sediments. Bedrock aquifers are hosted in discrete fracture zones within a wide range of consolidated bedrock lithologies and ages; There are very few regional-scale geologic cross-sections currently available for the South Cowichan area that demonstrate its aquifers’ hydrostratigraphic settings or connectivity. Groundwater flow directions have been inferred from the presence of prospective recharge zone (upland locations) and discharge zones (rivers, streams, lakes and marine environment). Groundwater flow directions in surficial aquifers are expected to be largely topography driven, while flow in bedrock aquifers may also be subject to site-specific geologic controls (location and interconnectivity of fracture zones); Surficial aquifers within the Study Area appear to be generally more productive than bedrock aquifers, but are highly variable from one aquifer to the next due to significant localized differences in media conductivity and stratigraphy; Government mapping suggests that bedrock aquifer productivities generally increase eastward within the Study Area, although this assertion appears to have been based on airlifted yields recorded at the time of well completion as opposed to evaluations of the region’s hydrostratigraphic settings and structural geologic regimes. Given the comparatively large surface extent of the area’s mapped bedrock aquifers and the currently inadequate level of understanding of their geological settings, significant opportunities may exist for increasing bedrock groundwater use. However, identifying productive bedrock groundwater zones (fractures) may prove to be technically challenging and costly; Total annual groundwater inflows from natural recharge within the South Cowichan area may range between 25 million m3 and 110 million m3 , with a best estimate of about 45 million m3 . Based on this best estimate recharge value and assuming that roughly 50% of total water usage within the Study Area originates from groundwater sources, it is estimated that about 30% of annual groundwater inflows may be currently allocated for water use, with the remainder (70%) being available for discharge to streams, lakes, wetlands and the marine environment. A portion of irrigation and domestic water use is also expected to end up as groundwater return flow (artificial recharge). Taking uncertainty of recharge into account, the confidence in these estimated percentages is relatively low; Areas where surficial aquifers are unconfined and may permit relatively high groundwater recharge rates, or areas where bedrock aquifers outcrop at the land surface or are overlain by a thin soil veneer, are expected to be characterized by relatively high groundwater vulnerability to surface contamination. A collaborative vulnerability mapping project for the area is currently being completed by others (the “Vancouver Island Water Resources Vulnerability Mapping Project”), the findings from which should form an integral part of the future South Cowichan area water plan; Groundwater recharge may potentially increase due to climate change, leading to a possible positive impact on water supplies. The degree to which this will occur is dependent on local geological constraints (for example, low permeability tills or massive bedrock might locally limit groundwater infiltration). Climate change may negatively affect groundwater resources through increased evaporation in areas where shallow water table conditions exist; Long-term trends in water levels measured for MOE observation wells in the Cherry Point aquifer were correlated against precipitation records. Water levels in this aquifer have declined in recent years, which have been attributed to increased groundwater use. This study suggests that water level declines may be due to a combination of groundwater withdrawals and natural fluctuations, given that the 2000 to 2005 period was characterized by below-average annual precipitation. Shallow domestic wells in particular appear to be very sensitive to either natural or anthropogenically-induced declines in water table elevation, as evidenced by the need for deepening of some domestic wells in the Cherry Point aquifer. The analysis of well hydrographs for the Cherry Point aquifer seem to confirm that surficial groundwater systems within the South Cowichan area may be highly sensitive to climate variability; and This study revealed the hydrostratigraphic complexity of the region’s groundwater aquifers, the current lack of quantitative information regarding these aquifers’ development and usage, and the general sparseness of reliable data. Consequently, the understanding of the Study Area’s groundwater resources at this time remains conceptual and largely qualitative in nature, which indicates the need for the development of an area-specific groundwater assessment to address current knowledge gaps. The development of a groundwater model for the region is recommended. This model could be used to distinguish between natural and anthropogenic pressures on groundwater flows, determine groundwater budgets on an aquifer-by-aquifer basis, support aquifer recharge zone and well-specific vulnerability assessments and protection strategies, and facilitate long-term water supply planning. Steps required to complete this new groundwater model development are outlined within this report. Surface Water The British Columbia Ministry of Environment’s (MOE’s) climate models predict that the availability of water within South Cowichan by the year 2050 may be influenced by increases to the average air temperature by 2 to 3°C and annual precipitation by 20%, that summers will be hotter and drier while the winters will be wetter, and that the frequency of 24-hr precipitation events greater than 80mm will increase; Monthly water balance models were developed as part of this project to estimate the current and future volume of surface water within the South Cowichan region. These models were based on unitarea runoff estimates, precipitation, lake evaporation, surface water abstractions, and climate change scenarios. The results of this modelling for all scenarios (current and future) suggest that an overall net annual surplus of surface water can be expected, with a significant excess of surface water during the winter months (December through March) and a slight deficit during the late summer months and early fall (note that monthly surface water balance deficits do not necessarily indicate that creeks and rivers are dry during the summer months, but that dry weather flows are maintained by release of water stored in lakes and groundwater base flows). The present calculated water balance for the South Cowichan area shows an annual net surplus of approximately 135 million m3 , increasing to 160 million m3 by 2036 as the result of drier summers, warmer temperatures, and increase demand. The 33% water efficiency goals set by British Columbia’s ‘Living Water Smart’ water plan only have a slight impact on the overall water balance, increasing the 2036 annual net surplus by 4%, with the summer/early fall months still in deficit; and Summer low flows in Lower Shawnigan Creek are detrimental to aquatic system health and are due in part to having insufficient lake storage to support both domestic use and downstream needs in summer. Low flow issues are also apparent in many creeks and streams within the South Cowichan area, including Garnett Creek, Johns Creek, and Spectacle Creek. These issues may be linked to excessive surface water diversion, decreased groundwater base flow, and/or climate variability. Knowledge Gaps and Issues Requiring Further Study It is recommended that a phased approach be adopted to develop a Water Management Plan for the South Cowichan area, with major existing knowledge gaps being addressed as stand-alone studies prior to development of the Plan. Recommended studies to be conducted prior to development of the Water Management Plan include the following: The acquisition of more detailed current surface water and groundwater withdrawal data is necessary to allow a better understanding of potential demand versus supply issues. This will require co-operation from major water users (improvement districts, etc.) and involvement from CVRD; A comprehensive, area-specific groundwater resource evaluation should be completed, which will culminate in the development of a numerical model that will establish detailed water budgets on an aquifer-by-aquifer basis. The groundwater resource evaluation and model development should take into account findings from MOE’s aquifer vulnerability mapping project currently being completed, and use the model to refine understanding of local aquifer vulnerabilities; A comprehensive, baseline surface water quality monitoring program should be undertaken. This program should include, at a minimum, the collection of surface water samples on a quarterly basis from the area’s key streams, lakes and reservoirs over a 1 to 2 year period. Prospective sampling locations should be identified through consultation with regional directors to identify potential areas of concern. Those locations for which the baseline program indicates possible water quality concerns could be incorporated in a longer-term monitoring program; and The potential effects of regional, national, and global pressures on population trend projections for the CVRD should be considered. Climate change could alter migration of people from areas experiencing water supply shortages or sea level increases. Economic upheavals and demographic shifts in Canadian society might also change housing choice and settlement patterns. The effects of such phenomena are difficult to anticipate and may increase the uncertainty in population trend projections for the CVRD. Water Management Plan Once the supplemental investigations and monitoring programs outlined above have been undertaken, a comprehensive Water Management Plan for the South Cowichan area can be developed to address issues raised by this preliminary study. Terms of Reference for the creation of this Water Management Plan are presented in this report. Completion of this Water Management Plan should result in the following tangible benefits: Enhanced understanding of local water issues; A workable management structure for each of Study Area’s three watersheds over a 30-year planning horizon that represents the interests of all stakeholders; and A sense of balance between the future water needs of agriculture, a growing population, and the ecosystems of the South Cowichan area. |
| Information Type | report |
| Regional Watershed | Vancouver Island South |
| Sub-watershed if known | Cowichan |
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| Project status | complete |
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