SECTION 10
Flows and Storage Report

Introduction

The water released from Wolf Lake that travels down Headquarters Creek into the Tsolum River is used for fisheries enhancement and is removed for agricultural irrigation . Additional losses result from evaporation, deep percolation and ground water seepage into the floodplain. Of these losses, seepage is believed to be more significant (Associated Engineering Services Ltd. (AESL) 1976).  In the summer of 1998, the TRTF installed five index wells for monitoring ground water seepage (Appendix A,  Table and Figure A.1). 

As pink salmon enter the Tsolum River in August or September they are confronted with high temperatures.  Low water levels also expose gravel bars in the lower river that present barriers to adult migration (Table and Figure A.2).  Increasing water flows through controlled releases provides more suitable conditions for adult migration and also benefits coho and trout fry rearing in the system.  The increased flow also provides benefits for the agricultural industry which withdraws water from the Tsolum River for irrigation (Figure A.3) .

Methodology

Wolf Lake Weir and Dam

While lake levels were low in August 1998, logs were removed from the weir by DFO staff.  Steel mesh was placed over the weir to provide increased stability before the concrete cap was poured to cover the mesh. After capping the weir with concrete, void spaces in the weir were filled with a no-shrink grout.

At the Wolf Lake outlet, a 5’ (1.53 m) wide slide gate at the base of a concrete dam allows release of lake water to Headquarters Creek. The dam slide gate is lifted by means of a worm gear.  The length of exposed thread is an indicator of the distance the gate has been lifted.  The gate overlaps the sill; therefore it must be lifted approximately 1 5/8” (4.1 cm) before water flows freely through the opening
(Appendix C Table C.1). 

The water flow through the gate depends on the size of the opening and on the head difference between the upstream (lake) and downstream sides of the dam (Appendix C Figure and Table C.2). At high lake levels water passes over a rock weir to enter the creek via a bypass channel.

Index Wells

The lower Tsolum River index wells, referred to as the Regional District of Comox-Strathcona (RDCS) wells, are located across the river from the WCS hydrometric station 08HB011 (200 m downstream of Rees Bridge).  They are 15.5 m and 25.3 m from the top of the stream bank. These wells were constructed by driving well points approximately 5 m into the ground using a manual post pounder. The well points are 1¼" x 18" sand points with 80 mesh screens.  Approximately 1.5 m of the well pipe is above ground level.  This exposed pipe is painted with fluorescent paint for easy detection.  In between measurements, a threaded cap is securely fastened on the top to prevent tampering (Appendix B, Figure B4). 

The other three index wells, known as the Cubitt wells are located on private property near Tsolum River road between Dove Creek and Headquarters Creek.  These wells are located 6.8 m, 14.1 m and 20.3 m from the riverbank.  Installing these wells entailed drilling with a 6" hand auger, placing the well casing, backfilling the hole and tamping.  These 3 m deep wells have a casing of 4" PVC sewer pipe. There were some difficulties encountered in choosing good sites for the wells and in well point installation.

The benchmark at the lower Tsolum River flow station is 5.51 m above mean sea level. This benchmark is also used for the flow station stage data.  A differential level survey was conducted to measure the elevation of the top of the two wells relative to the benchmark.  The level was proofed for accuracy before taking the measurements.

Well water depth measurements occurred weekly, from mid August to early September.  Stage or depth is measured with a Geotechnical Instruments pocket dip meter, model dm1.1m.  These measured values are related to the surveyed relative elevations. 

Stream Flow Measurement

Records for the WSC flow station in the lower Tsolum River (08HB011) cover the periods 1914-1920, 1955-57, and 1964 on.  This station is located approximately 14 km downstream of the Headquarters Creek hatchery, and is downstream of most pumping stations on the river.  The stream level is recorded hourly. A preliminary stage to flow conversion table for the lower Tsolum River is presented in Appendix C Table and Figure C.3
 The flow station on Headquarters Creek was established in June 1997 by WSC with support from DFO It is located at the Headquarters Creek hatchery approximately 6 km downstream from Wolf Lake. 

Results

Wolf Lake Water Levels and Water Release

On August 14, 1997 at 10:35 the gate at the dam was lifted to give an opening of approximately 2¼”.  At 12:00 this was decreased to an opening of 11/16” (1.1 cm).   It was opened to 2” (5 cm) on August 15 (15:40); 3” (7.6 cm) on August 18 (15:15); 4” on August 19 (15:43) and 5 inches on Sept 8 (11:30).   Appendix C Table C.4,  summarizes flow changes resulting from these releases.   A stepped release pattern is used to avoid abrupt changes in downstream flow that could endanger swimmers.

On August 14, 1998 at approximately 09:30 the gate was opened to approximately 1” (2.5 cm).  The gate was opened to 2” (5 cm) on August 17 (10:37); and 3” (7.6 cm) on August 19. A record of 1998 gate operation dates and the resultant flow in Headquarters Creek and the Tsolum River are presented in Appendix C, 

Flows

Stream water losses are determined using the hourly recorded flow data.  This assumes negligible inputs from other Tsolum River tributaries. It is further assumed that the watershed water balance remains stable over several hours. 

In 1997, there were minimal water losses.   The negative loss values may be attributed to measurement error.  During the 1997 Wolf Lake water releases, less than 20% of the water was lost.  Expected losses due to evaporation, seepage and water withdrawals did not materialize.  This may be due to rainfall in June and July, and the short dry period in August (Figure C4).  This precipitation would result in a higher water table and lower summer irrigation requirements.

Calculated water losses for 1998 are as high as 64%. Comox airport summer precipitation data for 1998 reveals a dry summer, compared with 1997.  Seepage losses are expected with the resulting lower water table.  During hot dry weather, irrigation demands and evaporative water losses are higher. If the seepage losses from the river could be accurately measured and predicted, the timing and amount of the water release from Wolf Lake could be optimized for fish survival.

After the lake water is released, there is a time lag before the increased stream flow reaches the measurement stations at Headquarters Creek Hatchery (6 km downstream), and the lower Tsolum station (20 km downstream).  Response time varies between three and six hours for the water to reach the hatchery, and between 11 and 31 hours for water to reach the lower Tsolum station.  The time lag is shorter as water moves faster at higher flows.

There is no simple relationship between the flow released from Wolf Lake and water temperature in the lower Tsolum River.  Although Wolf Lake was the warmest site monitored in this study, water released from the lake does not raise water temperatures downstream because the temperature of water released from the lake is modified as the water flowing downstream makes contact with the atmosphere.  The decrease in mean daily water temperature of 4oC (Figure C.4) in the lower Tsolum River in mid August coincided with lake releases, but was actually due to a cooling trend in the weather.  Mean daily air temperature at the Comox Airport dropped 9oC between August 13 and 16.  This cooling trend preceded a few days of light rain and caused a drop in water temperature throughout the watershed.

Index Wells

Recommendations

1. The lake is shallow (2 to 2.5 m) near the outlet into Headquarters Creek.  If water were to be piped to the dam from the north end of the lake it would be possible to access cooler water from the deeper areas of the lake (39 m maximum depth).  A temperature and depth study should be completed in 1999 to provide data on the lake’s thermal profile.

1. Debris jamming at the Wolf Lake dam occurred in September 1998. To avoid re-occurrence, a boom and debris catcher should be placed at the lake outlet. 

1. The climatic data referred to in this report is for the Comox airport weather station. It would be beneficial to continuously monitor rainfall within the Tsolum River watershed.  A data logger monitored rainfall gauge is proposed.

1. Flow stations should be calibrated before water releases.  This should take place in the first two weeks of August. 

1. Consideration should be given to increasing downstream flows in the future.  During the dry months of August and September 1998, there was no problem releasing enough water to maintain a 15 cfs flow rate.

1. The upstream Cubit wells are correlated with a stream flow station.  A flow station should be installed near the well location.

1. More frequent measurement at additional points in the flood plain, are necessary to correlate lag time between river flows and ground water levels to predict seepage losses.   Continuous monitoring of well water levels could be carried out with the use of electronic data loggers.

References

• Associated Engineering Services Limited (AESL) Wolf Lake Study  1976.  Report prepared for the Department of the Environment  Fisheries and Marine Service

• BC Environment 1992.  Allocation Policy of Regional Water Management Branch, Vancouver Island Region.  BC Ministry of Environment, Lands and Parks, Province of BC 1992.

• Busto, Vince. 1998. Business letter to: Kathy Campbell, Tsolum River Task Force Project Coordinator, Merville, BC; from Vince Busto, Department of Fisheries and Oceans, Habitat and Enhancement Branch, Vancouver, BC.  June 4, 1998.

• McLean, William. 1999. Operational Support Biologist, Quinsam Hatchery, Department of Fisheries and Oceans Canada, Campbell River, BC. Personal Communication, March 9, 1999.

• Walsh, M.G. 1997.  Untitled bathometric survey map of Wolf Lake. British Columbia Fish and Wildlife Branch.   May 14, 1977.

• Table A.2 Low Flow Obstructions, Tsolum River
•  Figure A.2 Map of Tsolum River Low Flow Obstruction Sites
•  Figure A2 Map of Tsolum River Withdrawal Pipes

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