Quamichan Lake Outlet Control
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Report No. 9073-1 Quamichan Lake Outlet Control Prepared for: Friends of Quamichan Lake Stewardship Committee Prepared by: D.G.V. Engineering Services Ltd. February 1, 2008 TABLE OF CONTENTS Page 1. OVERVIEW ..................................................................................................1 2. INTRODUCTION ..........................................................................................3 2.1.1 Hydrology: ...............................................................................4 2.1.2 Survey of the Lake Outlet Channel..........................................5 2.1.3 Control Structure Concept: ......................................................5 2.1.4 Management of Beaver Activity: ..............................................7 2.1.5 Management Regime of Lake Level and Creek Discharge......9 2.1.6 Habitat Loss Footprint............................................................10 2.1.7 Channel Maintenance............................................................10 2.1.8 Monitoring..............................................................................10 3. DISCUSSION .............................................................................................10 3.1 Lake Level Data ................................................................................10 3.1.1 New Reference Mark .............................................................11 3.1.2 Water Survey of Canada (WSC) station 08HA020 ................11 3.1.3 Stewart Data (6387 Lakes Road):..........................................11 3.1.4 Dr. David Groves ...................................................................12 3.2 Quamichan Creek Flow.....................................................................12 3.2.1 Water Survey of Canada (WSC) station 08HA021 ................12 3.3 Channel Capacity ..............................................................................12 4. DEVELOPING STORAGE FOR FISH ENHANCEMENT............................13 5. CONCLUSION AND RECOMMENDATIONS .............................................14 6. DISCLAIMER..............................................................................................15 7. CERTIFICATION ........................................................................................16 8. ATTACHMENTS.........................................................................................17 4-Feb-08 D.G.V. Engineering Services Ltd. i 9073-1 Outlet Control Report Final lp.doc Nanaimo, BC Quamichan Lake Outlet Control Quamichan Lake Outlet Control 1. OVERVIEW DGV Engineering Services Ltd. was retained to review the conditions that impact the water level and outflow of Quamichan Lake, near Duncan BC. The terms of reference included the following items: • Limited hydrological assessment • Site survey using land survey techniques • Site materials evaluation and mapping • Fisheries compensation area evaluation • Conceptual weir design(s) and location(s) • Recommendation for a management regime The terms of reference did not include: • Assessment of Fish Habitat • Assessment of factors related to fisheries productivity • Assessment factors around water flow that related to fish migration, spawning or rearing • Assessment of Water Quality • Public education issues related to beaver activity or beaver management This report addresses each of these items in terms of providing some basis for attempting to address the lake management conflicts that exist. The community issue that needs to be addressed is the need for, and nature of, the management of the lake water level. Agricultural interests around the lake are best served by a lower lake level in the spring and early summer, thus allowing access to low lying productive land areas. Generally, higher lake levels best serve fisheries and wildlife habitats by providing some storage that could be used to improve summer stream flows. Under current conditions, an active beaver dam in the outlet stream has eliminated effective creek flows thus defeating both the access to low lying lands by the farms and fish passage. 4-Feb-08 D.G.V. Engineering Services Ltd. 1 9073-1 Outlet Control Report Final lp.doc Nanaimo, BC Quamichan Lake Outlet Control The Friends of Quamichan Lake Stewardship Committee has questioned whether a control structure could be installed to operate such that: ¾ Early spring lake levels would be dropped to facilitate farm land access. The current channel, if clear, has provided adequate access to farm lands. However if free drainage is allowed to continue throughout the spring Quamichan Creek will be dried in the summer. ¾ When the lake level is low enough to allow drainage and access to the farm land, the flow from the lake would be reduced and controlled so that the lake level would achieve limited recovery by holding water from late spring rains. The lake level would thus be controlled to promote the aquatic environment, but still low enough to aid the farmers throughout the summer period. ¾ Some of the retained storage would be available in the late summer to assist in fish migration. ¾ Fish passage would be maintained past the structure for a larger portion of the year. The existing creek channel is an excavated channel that is founded on bedrock. The channel has essentially no slope from the lake outlet near the existing footbridge at Art Mann Park for at least 160 m to the old stream flow station on private property. This excavated flat channel in rock extends an estimated 150 m further downstream before a clearly defined break in slope where the stream begins to lose elevation. The main impediment to lowering of the lake level to recent "normal" water levels is the existing beaver dam and its associated mound of debris and sediment. Removal of this obstruction will immediately lead to lowering of the lake water level and may expose other important flow obstructions upstream. In general, the channel has a considerable amount of woody debris and overhanging material, but despite this the channel has reasonable hydraulic capacity. The channel capacity is primarily limited by the lack of slope. Inspection and hand clearing of specific flow impediments on a regular basis are preferred over the wholesale machine clearing of the creek bed if aesthetic and environmental impacts are to be minimized. There is no easy means by which a significant lowering of the summer lake levels can be achieved. Lowering summer lake levels more than could be achieved through simple clearing of the creek bed would involve deepening the channel in bedrock over approximately 310 m of length since the creek is typically essentially dry in the summer. A simple control structure is suggested that could provide some active manipulation of the lake water level in the summer, presumably with the intent of early lowering of the lake level by unrestricted drainage followed by attempting to restrict discharge in May and June to hold water in the lake to maintain and possibly raise lake levels. 4-Feb-08 D.G.V. Engineering Services Ltd. 2 9073-1 Outlet Control Report Final lp.doc Nanaimo, BC Quamichan Lake Outlet Control Any proposed lake management strategy must consider the compromise between agricultural land access and residential and recreational uses of the lake, water supply for the water license holders and environmental concerns. The operational rules would result from input from these interests and are therefore beyond the scope of this study. 2. INTRODUCTION Quamichan Lake is a relatively large shallow lake located approximately 2 km north east of Duncan. The lake has an area of 288 hectares, a mean depth of approximately 4 m, and a watershed catchment area of about 18.8 km2. The general topography is shown in Figure 21 and the lake bathymetry is illustrated as Figure 32. The lake occupies part of the relatively flat lowland area formed by glacial infilling and surrounded by relatively steep bedrock structures including Mount Tzouhalem to the east, Maple Mountain and Mount Richards to the north and Mount Prevost to the west beyond Somenos Lake and wetlands and the northern portion of Duncan. The area immediately around the lake is fully developed primarily for agricultural and rural residential uses. The watershed boundaries are somewhat indistinct to the west due to imposed road and agricultural drainage structures that likely modify the natural drainage structure as well as possible sub-surface connections with the Somenos Lake and wetlands. The lake appears to be defined by shallow bedrock at the margins, particularly at the outlet where Quamichan Creek drains the lake 1.25 km to the south where it joins the Cowichan River. The lake provides habitat for Brown Catfish, Rainbow and Cutthroat Trout. Quamichan Creek is a migration route for fish between the lake and the Cowichan River, and likely provides rearing habitat. The creek and associated riparian area is habitat for a variety of wildlife. The intent of the study is to correlate the various lake level datasets, define the discharge character of Quamichan Lake and develop a structure concept that may provide some control of the lake levels. High spring lake levels adversely impact agricultural activities, while low to zero flows in the summer are detrimental to fish values. 1 From NTS 1:50 000 map, 92 B/13, Published by Energy Mines and Natural Resources, Canada 2 From Ministry of Environment, BC 4-Feb-08 D.G.V. Engineering Services Ltd. 3 9073-1 Outlet Control Report Final lp.doc Nanaimo, BC Quamichan Lake Outlet Control The study involved land survey of the