«Table of Contents Table of Contents List of Tables List of Figures Appendices 1.0 INTRODUCTION 2.0 GENERAL WATERSHED INFORMATION 2.1 Plan Area 2.2 History ...»
5.2 Domestic Water Demand
Despite the larger number of domestic water licences, the licenced domestic water demand represents only 4.1% of the total average annual demand. Of the 28 domestic water licences on Denman Island 5 are on springs (10,700 gpd - 4.4 dam3 low flow demand), 8 are on Chicadee Lake (8,000 gpd - 3.3 dam3 low flow demand), 6 are on Graham Lake (6,000 gpd - 2.5 dam3 low flow demand), 5 are on creeks and brooks (4,700 gpd - 1.9 dam3 low flow demand) and 2 are on swamps (1,500 gpd - 0.6 dam3 low flow demand).
Of the 25 domestic water licences on Hornby Island 18 are on springs (12,500 gpd - 5.1 dam3 low flow demand), 5 are on creeks and brooks (2,500 gpd - 1.0 dam3 low flow demand) and 2 are on swamps (1,100 gpd - 0.4 dam3 low flow demand). Most of the springs on Hornby Island are situated around the base of Mount Geoffrey.
Except for local competition for water on small streams and springs, domestic demand is not significant.
5.3 Industrial Water Demand The water demand under this category would be better described as commercial or agricultural demands; but under the Water Act Regulations are categorized as subcategories under the industrial water demand category for purposes of water licensing.
One of the two industrial purpose water licences is for 500 gpd (0.2 dam3 low
DENMAN & HORNBY ISLANDS WATER ALLOCATION PLAN
5.4 Irrigation Water Demand Irrigation water demand is the largest demand and will have the most significant impact on low flows. Irrigation water demand occurs only during the low flow period when competition for water is the greatest.
There are 13 irrigation water licences on Denman Island. The largest irrigation water licences is 40 acft (49.3 dam3) from Cicero Slough; a tributary to Graham Lake.
It is supported by a 40 acft (49.3 dam3) storage dugout in the slough. The second largest irrigation licence is 18.0 acft (22.2 dam3) on Lacon Lake which is likewise supported by 18.0 acft (22.2 dam3) of storage in Lacon Lake. The remaining irrigation water licences from Chickadee Lake and swamps, brooks, creeks and sloughs are less significant. Most irrigation demands on Denman Island have supporting storage water licences.
There are 13 irrigation water licences on Hornby Island. The three largest irrigation water demands are 65 acft (80.2 dam3) on Harry Spring, 61.7 acft (50 dam3) on Slade Spring, 30 acft (37.0 dam3) on Rubinoff Spring and 20 acft (24.7 dam3) on Maude Spring. The latter two water licences have supporting storage. Most of the irrigation demand on Hornby Island is not supported by storage.
5.5 Storage Water Demand
There are 27 water licences for storage purpose within the plan area. Storage demand is the second largest licenced water demand and supports municipal waterworks and the irrigation demand noted above. However adequate storage has not been developed to supply and support the licenced irrigation demands during the low flow period.
5.6 Land Improvement Water Demand There is one water licence for land improvement on Denman Island. The licence is for the development, on a small marsh, of a decorative pond and dyke to prevent
DENMAN & HORNBY ISLANDS WATER ALLOCATION PLANflooding of neighbouring lands. These improvements have no significant impact on flows and other licenced demands.
5.7 Conservation Water Demand There is one water licence for conservation purpose on Denman Island. This water licence is held by the Ministry of Environment, Lands and Parks, authorizes the construction of a small dam in McFarlane ditch and the storage of 150.0 acft (185.0 dam3) of water in McFarlane Swamp. The dam, reservoir and other improvements were constructed by Ducks Unlimited to develop and improve a wild foul refuge.
This water licence for conservation purposes does not create a significant consumptive demand and provides storage for a domestic and small irrigation demand.
5.8 Projected Demand There are only 17 water license applications pending as of July 1993. These pending water licence application demands are for 36.4 dam3 (29.5 acft) irrigation purpose, 5.2 dam3 (6,250 gpd) domestic purpose, 0 dam3 industrial (fire protection) purpose and 5.6 dam3 (4.5 acft) storage purpose. The storage purpose is intended to support the 2 small irrigation demands.
Future water demands are anticipated to be similar to existing licenced water demands. Future water demands in the plan area will primarily relate to domestic, irrigation and conservation. These water demands will require that winter high flows be stored for summer low flow demands (supporting storage).
6.0 CONCLUSIONS and RECOMMENDATIONS
Within the plan area the low flow period is the six months from May through October; when the flow is below 20% of the mean annual discharge (MAD). There is no significant flow in any stream during the five months of June through October in some lower than average flow years. The minimum mean monthly flow is 0.0 litres/second in July.
Mean monthly flows higher than 20% MAD occur from November through April (6 months). The mean monthly flow is above 60% MAD for the period of November through March (5 months). Therefore there is considerable flow available for part of the
There is no significant fish resources identified in any of the streams on Denman or Hornby Islands except in Graham Lake and in Chickadee Lake. Both Graham Lake and Chickadee Lake on Denman Island support resident fish populations. There may be some potential fish habitat and marginal fish habitat in other drainages within the plan area, however there is no evidence of significant fish utilization and low flows will limit any potential fish habitat utilization.
It is recommended that Fish screens be required on water intakes in Graham Lake and Chickadee Lake.
The licenced water demand on Denman and Hornby Islands are for irrigation, storage, conservation, municipal waterworks, industrial, domestic and land improvement purposes. The most significant water demands are for irrigation, storage and conservation purposes. As little or no flow occurs during the low flow period of May through October, licenced water demand during this period requires storage to support and ensure water supply. There is not sufficient storage developed or proposed to maintain and support the existing and projected water demands through the low flow period.
It is recommended that no further significant allocation of water be made unless licence application demands (and existing demands where the licensee is expanding the supply) are supported with proposed storage. Where there is no natural storage (ie. lakes, swamps or marshes), or where natural storage is inadequate for water demands, storage reservoirs (dams or dugouts) may be developed to supply water demands.
Potential for development of storage may exist in marshes, swamps, ponds and small lakes such as The Swale, The Maddigan, Morrison Swamp and Pickles Swamp.
Drainage improvements for cultivation have reduced the water supply in several of the large swamps and marshes.
Graham Lake and Chickadee Lake are the only identified sources of water supply on the islands where significant natural storage volumes may still be available.
6.1 Graham Lake Existing licenced supporting storage for municipal waterworks demands is 46.9 dam3 (38.0 acft). The 12,045,000 gallon per year municipal waterworks licenced water demands (27 dam3 - 90 day low flow demand) are adequately supported by the storage
To maintain fish habitat in the lake, no more than an additional 0.6 meters (2 feet) of water from the natural lake control elevation should be withdrawn from Graham Lake. The natural lake control elevation is 0.3 metres (1.0 ft) below the spillway elevation of 33.4 metres GSC.
It is recommended that the surface of Graham Lake should not be drawn down below elevation 32.5 metres GSC. Assuming a 0.3 metre (1.0 ft) evaporation loss from the natural surface of the lake (36.0 dam3), the additional volume of water available in Graham Lake for extractive use during the summer months is
34.0 dam3 (27.6 acft).
6.2 Chickadee Lake To maintain fish habitat in the lake, no more than 0.6 meters (2 feet) of water from the natural lake control elevation should be withdrawn from Chickadee Lake. The natural control elevation of Chickadee Lake is at the invert of a road culvert at elevation
51.06 metres GSC.
It is recommended that the surface of Chickadee Lake should not be drawn down below elevation 50.5 metres GSC. Assuming a 0.3 metre (1.0 ft) evaporation loss from the natural surface of the lake (40.0 dam3), the volume of water available in Chickadee Lake for extractive use during the summer months is 35.0 dam3 (28.4 acft).
6.3 Municipal Waterworks Waterworks purpose in the Water Act is the carriage or supply of water by a municipality, improvement district, regional district or private utility for the purpose of providing water to a residential area.
The local populations of Denman and Hornby Islands have reacted negatively to any significant residential development on the islands. Local zoning by-laws and public concern for the maintenance of a rural lifestyle on the islands may limit any further urban size residential development and thus municipal waterworks demands.
If a residential development is permitted then storage must be developed to support the waterworks demand. The applicant for a waterworks demand shall be require to assess the supply for a ten year projected demand and provide evidence that
DENMAN & HORNBY ISLANDS WATER ALLOCATION PLANthe projected demand is not excessive in comparison with adjoining community demands, water conservation is being promoted (ie. residential meters, pricing practices, education) and adequate system balancing storage (ie. volume difference between maximum hour and maximum day demands) will be constructed or is available for peek hour demands. Water Utilities will also have to provide evidence that the appropriate requirements for a Certificate of Public Convenience and Necessity (CPCN) have been met and a CPCN will be obtained. Licenced allocations will be limited to a 10 year projected demand except where the applicant can provide satisfactory evidence that a longer projection period is required (ie. because the cost of construction of works must be amortised over a longer period).
The licensee shall be required to meter or measure and record the water diverted from the source stream.
The licensee shall be required to treat the water supply in accordance with Ministry of Health requirements.
Adequate system balancing storage shall be required to ensure that the rate of withdrawal from the source during short term or maximum hour demand does not exceed the maximum daily demand. Good conservation techniques must be practised at all times and no increase in the amount of water in existing community waterworks licences shall be allowed unless meters and other conservation measures have been used.
A domestic water licence shall be 2,273 litres per day (500 gallons per day) maximum daily demand for each rural dwelling as indicated on the plan attached to the water license application. This amount will allow for the maintaining of 0.10 hectares (0.25 acres) of garden associated with the dwelling. Domestic water licences shall not be issued solely to maintain green lawns and gardens where groundwater and other sources of water supply provide the primary domestic household needs.
Domestic water licence shall not be issued to provide evidence of an "adequate potable water supply" to subdivision approval authorities for subdivision development.
Large subdivision of land for residential development (more than 10 residential lots) shall be encouraged to develop and use a municipal waterworks (community) water system.
To ensure an adequate domestic water supply for household uses, from a
DENMAN & HORNBY ISLANDS WATER ALLOCATION PLANsurface water source, applicants shall be required to develop storage or use the water naturally stored in marshes, swamps, ponds or lakes. The quantity of storage required is the average daily demand of 1,136 litres per day (250 gpd) for a five month period (150 days), say 170 m3 (6,000 ft3) or 0.2 dam3 (0.1 acft). This requires a reservoir or dugout approximately 6 metres (20 ft) wide by 9 metres (30 ft) long, with an average depth of 3.5 metres (11 ft); allowing approximately 0.3 metres (1 ft) for evaporation loss.
A water licence for domestic use shall not be issued to a residence within a community water supply area unless written leave to do so is obtained from the community water supply agency.
6.5 Industrial Industrial water licenses on Denman and Hornby Islands are uses typically associated with small household commercial and agricultural enterprises. Also water demands for small resort or bed and breakfast and stock watering enterprises may be anticipated.
Industrial demands related to commercial and resort development should be handled similar to multiple domestic demands with the same requirements. Livestock requiring more than 450 l/day (100 Igpd) are to be considered an Industrial (agricultural) demand. Cattle or livestock requiring 450 l/day (100 Igpd) or less will be considered a
Domestic (livestock) demand. Estimated livestock demands are:
Different crops and their rooting depth and water availability coefficient were classified into shallow (0.5 metre) and deep (1.0 metre) effective rooting depths. The available water storage capacity (AWSC) was estimated for shallow and deep root zone depth for classes of similar soil associations identified on the maps in the publication Soils of Southern Vancouver Island (J.R. Jungen, P.Ag., Ministry of Environment, August 1985).
Where composites of two or three soil associations are intermixed or occupy such small areas that they cannot be separated at the scale of the mapping, only the predominant soil association was considered. The following table was made using the climatic information for Parksville and the AWSC for different crop effective rooting depth classes and soil classes. A colour map of irrigation requirements is provided in Figure 7.
If the applicant for a water licence can provide more specific soil assessment information for a given area, that soil assessment may be used to assess irrigation demands.
It should be noted that these annual irrigation water requirements are for sprinkler irrigation systems only.
Irrigation gun or flood irrigation systems require greater irrigation quantities and should be discouraged. If irrigation gun and flood irrigation practices are to be used then suitable meters shall be installed and water withdrawals limited to the equivalent annual irrigation requirements for sprinkler systems. As the equivalent annual irrigation water requirements for sprinkler systems may not be adequate to sustain crops using these less efficient methods of irrigation, the applicant may be required to reduce crops, limit the acreage irrigated or convert to a more efficient sprinkler irrigation system.
Trickle irrigation can reduce water requirements by 35% and should be encouraged where practical.
The maximum irrigation system flow rate shall not exceed 19.1 l/sec (4.2 imperial gals. per minute) per 0.4 hectare (1 acre), and users must be encouraged to employ good agricultural practices (field size, system selection and farm management) to conserve water.
The authorized period of use for irrigation shall be from April 1 to September 30.
All irrigation water demands must be supported by storage development. Storage required to support irrigation demands is the total required amount as per crop and soils, plus an additional allowance for evaporation and other losses from the storage reservoir.