Comox Lake and Puntledge River Temperature Modelling Study
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Fisheries and Oceans Canada COMOX LAKE AND PUNTLEDGE RIVER TEMPERATURE MODELLING STUDY FISH.073 July 2004 HAY & COMPANY CONSULTANTS INC. One West 7th Avenue Vancouver, BC V5Y 1L4 www.hayco.com Comox Lake and Puntledge River Temperature Modelling Study July 2004 EXECUTIVE SUMMARY The Puntledge River flows from Comox Lake to Comox Harbour on the east coast of Vancouver Island, BC, and provides important spawning and rearing habitat for salmon. A storage dam at the outlet of the lake and a diversion dam on the river are used to control lake levels and river flows. Fisheries and Oceans Canada (DFO) is considering cold lake water withdrawal from Comox Lake as an option to reduce water temperature in the Puntledge River in the summer months, since high temperatures experienced in the river are a negative stressor for fish. This report presents a modelling study of lake and river temperatures. A prediction system, consisting of three numerical models, has been developed for the simulations of water level, velocity and temperature in both Comox Lake and the Puntledge River. Circulation within Comox Lake was simulated using Hay & Company’s proprietary three-dimensional hydrodynamic model H3D. The model is able to capture the important processes of the development of thermal stratification over the course of the year as it evolves from the uniform conditions of winter, through the stratified conditions of summer, to the turnover during fall. The model is driven by heat exchange at the lake surface, wind forcing and river inflows. The outflow from the lake was modelled in two ways. For the existing condition, outflow was through shallow submerged gates in the Comox Dam; the deep-water withdrawal was modelled as an extraction from a depth of 35 m. Withdrawing the colder deep water results in a warming of the lake water down to about 40 m depth over the summer and fall, with a maximum temperature difference of over 5 degrees compared to the surface withdrawal simulation. The outflow from the lake model for the two runs was used to create two series of inflow temperatures for the Puntledge River model. The river temperature model is an implementation of H3D, which simulates changes in river temperatures due to meteorological forcing and mixing of tributary waters. A major modification for the Puntledge River implementation was the provision for heat flux into and out of the rock bed of the river. Another major change was ‘flattening’ the river. If the entire 125 m elevation drop over the river’s length were to be modelled, the grid would be computationally expensive. Instead, the one-dimensional model MIKE 11 was used to generate the mean geodetic water surface elevation, which was then used to calculate the gravity force in the three-dimensional model. This accounts for the true surface slope while conducting calculations on a flattened grid with no elevation drop. The river bathymetry was generated from a topographic survey of the Puntledge River conducted in 2002. Water levels from the same survey were used to calibrate the river model. Water temperatures have been collected at seven sites on the Puntledge River since 1999. The temperatures were used as input temperatures for the river model as well as to validate the river model. Two simulations were performed, one with the existing surface water supply, and the second with the deep lake withdrawal, to evaluate the impact of the cold water withdrawal on river temperatures. Supplying water from the deep withdrawal in the lake results in much cooler river temperatures. The FISH.073 i Comox Lake and Puntledge River Temperature Modelling Study July 2004 average temperatures along the river, based on a reach-by-reach comparison, decreased by as much as 5.5 degrees in the hottest month of August, compared to the surface supply. The maximum river water temperature in August was about 16 degrees with the deep withdrawal, compared to a maximum of over 20 degrees with the current surface withdrawal. These cooler temperatures would be beneficial for fish migrating up the Puntledge River during the warm months. FISH.073 ii Comox Lake and Puntledge River Temperature Modelling Study July 2004 TABLE OF CONTENTS 1 INTRODUCTION ................................................................................................................................ 1 1.1 Background................................................................................................................................... 1 1.2 Context.......................................................................................................................................... 2 1.3 Technical overview....................................................................................................................... 2 2 LAKE MODEL..................................................................................................................................... 3 2.1 Model description ......................................................................................................................... 3 2.2 Input data ...................................................................................................................................... 4 2.3 Calibration..................................................................................................................................... 5 2.4 Comparison of surface and deep water withdrawal ...................................................................... 6 3 RIVER MODEL ................................................................................................................................... 7 3.1 Field Survey.................................................................................................................................. 7 3.2 1-D Hydrodynamic River Model .................................................................................................. 9 3.3 3-D River Temperature Model.................................................................................................... 10 3.3.1 Description.......................................................................................................................... 10 3.3.2 Water level calibration........................................................................................................ 11 3.3.3 Temperature calibration ...................................................................................................... 12 3.3.4 Deep water withdrawal simulation...................................................................................... 13 4 CONCLUSIONS AND RECOMMENDATIONS ............................................................................. 15 5 REFERENCES ................................................................................................................................... 16 FISH.073 iii Comox Lake and Puntledge River Temperature Modelling Study July 2004 LIST OF FIGURES Fig. 1.1 Map of Comox Lake and Puntledge River, with 1999 average annual flows Fig. 2.1 Lake-headpond model 100-m grid Fig. 2.2 Measured and modelled lake temperature profiles Fig. 2.3 Comox Lake temperatures: spring, summer, fall 1998 Fig. 2.4 Lake-headpond model vs. measured water temperature, 1999 Fig. 2.5 Drawdown of warm water with surface withdrawal Fig. 2.6 Lake profiles, deep vs. surface withdrawal Fig. 2.7 Difference in lake temperature (May, June, July 1999) Fig. 2.8 Difference in lake temperature (August, September, October 1999) Fig. 2.9 Heat in lake-headpond model, deep vs. surface withdrawal Fig. 2.10 Change in sluicegate temperature, deep vs. surface withdrawal Fig. 3.1 River survey key plan Fig. 3.2 River survey longitudinal profile Fig. 3.3 Headpond contours Fig. 3.4 Headpond cross-sections Fig. 3.5 Surveyed cross-sections 1, 2, and 3 Fig. 3.6 Surveyed cross-sections 4, 5, and 6 Fig. 3.7 Surveyed cross-sections 7, 8, and 9 Fig. 3.8 Surveyed cross-sections 10, 11, and 12 Fig. 3.9 Surveyed cross-sections 13, 14, and 15 Fig. 3.10 Surveyed cross-sections 16, 17, and 18 Fig. 3.11 Surveyed cross-sections 19, 20, and 21 Fig. 3.12 Surveyed cross-sections 22, 23, and 24 Fig. 3.14 Surveyed cross-sections 25, 26, and 27 Fig. 3.15 Surveyed cross-sections 28, 29, and 30 Fig. 3.16 Surveyed cross-sections 31, 32, and 33 Fig. 3.17 Surveyed cross-sections 37 and 38 Fig. 3.18 Surveyed cross-sections 27a and 28a Fig. 3.19 Surveyed cross-sections 29a and 30a Fig. 3.20 Puntledge River MIKE 11 implementation Fig. 3.21 Surveyed and modelled water levels along Puntledge River FISH.073 iv Comox Lake and Puntledge River Temperature Modelling Study July 2004 Fig. 3.22 Modelled and surveyed water levels and bathymetry in Puntledge River (chain 16465 to 15066) Fig. 3.23 Modelled and surveyed water levels and bathymetry in Puntledge River (chain 14401 to 12870) Fig. 3.24 Modelled and surveyed water levels and bathymetry in Puntledge River (chain 12128 to 10034) Fig. 3.25 Modelled and surveyed water levels and bathymetry in Puntledge River (chain 9439 to 8535) Fig. 3.26 Modelled and surveyed water levels and bathymetry in Puntledge River (chain 8043 to 6618) Fig. 3.27 Modelled and surveyed water levels and bathymetry in Puntledge River (chain 6414 to 4246) Fig. 3.28 Predicted tide, surveyed levels and modelled water level at mouth Fig. 3.29 Temperature sensor locations Fig. 3.30 Puntledge River modelled and measured water temperature, 1999 Fig. 3.31 August river temperature, surface vs. deep input Fig. 3.32 Division of Puntledge River model into reaches Fig. 3.33 River