Appendix 4.3C
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REGIONAL CUMULATIVE EFFECTS ASSESSMENT – PHASE II PHYSICAL ENVIRONMENT – WATER REGIME – APPENDIX 4.3C APPENDIX 4.3C: AN ASSESSMENT OF THE HYDRAULIC IMPACTS OF THE CHURCHILL RIVER DIVERSION ON THE RAT AND BURNTWOOD RIVERS ____ ANASSESSMENT OF THE HYDRAULIC IMPACTS Of THE CHURCHILL RIVER DIVERSION ON THE RA TAND BURNTWOOD RIVERS WaterResources EngineerIng PowerPlanning DivisIon PREPARED BY J. CRAwFORD, RENG. \Ak(Rk---’ CHECKED BY J. MALENCHAK, PH.D. P.ENG. J. WEsTMAc0TT, M.Sc. P. CHANEL, M.Sc. PENG. / P. RASMUSSEN, PH.D. P.ENG. ? CONSULTANT APPRovED BY E,TEKLEMARIAM, M.Sc. RENG. NOTED BY T.MILES, M.Sc. RENG. — i)iC DATE: NOVEMBER 6,2015 REPORT: PPD-1 5/10 1kManitoba Hydro 2 EXECUTIVE SUMMARY 1. The following is a report on simulated water levels and river flows for the Rat and Burntwood Rivers without the Churchill River Diversion. Simulated water levels and river flows are required to estimate the hydraulic impacts of the Churchill River Diversion for Regional Cumulative Effects Assessment and for other purposes including for operations and resource planning. 2. A hydraulic model was developed to simulate hydraulic conditions on the Rat and Burntwood River systems without the Churchill River Diversion. Model results were then compared against actual measured values to quantify the impacts of the Churchill River Diversion and verify the model was working correctly. Overall model performance results were good which confirmed the model is representative of conditions without the Churchill River Diversion. The following conclusion can be made from the model results: The Churchill River Diversion has impacted the Rat and Burntwood River systems. The average flow on the Rat River at the site of the Notigi Control Structure has increased from 23 cms without the Churchill River Diversion to 790 cms with the Churchill River Diversion for the period from January 1, 1978 to December 31, 2014. Prior to the Churchill River Diversion river flows followed a typical seasonal pattern with generally higher flows in the summer and lower in the winter. The Churchill River Diversion has changed the water regime of the Rat River by changing the quantity of flow, the seasonal timing of flow and the magnitude of flow fluctuations as outflows from Notigi are now set to meet the power requirements of the Manitoba Hydro system. 3 The first impacts of the Churchill River Diversion on the Rat and Burntwood River Systems occurred on May 8, 1974 when the Rat River at Notigi was closed by cofferdam to allow for the construction of Notigi Control Structure. All river flows upstream of the cofferdam were closed off for a period of approximately 19 months which resulted in near zero flow and extremely low water levels downstream. The first diversion water began flowing from the Churchill River basin to the Rat River basin on June 2, 1976 when the rock plug at South Bay Channel was removed. Operation of Notigi Control Structure first began on September 1, 1976 when the flow was increased from near 0 cms to 200 cms over a 3 day period. The initial operation of Notigi was limited during the first winter of 1976/77 to 311 cms so as to not exceed maximum state of nature water levels downstream. Notigi outflows were subsequently increased to the Licence maximum of 850 cms in a series of steps beginning on May 13, 1977 and ending on August 20, 1977. The Churchill River Diversion has had an impact on water levels along the Burntwood River. The average water levels of Wapisu, Threepoint/Footprint, Wuskwatim, Opegano and Birchtree Lakes for the period from January 1, 1978 to December 31, 2014 have risen by 5.7 metres, 4.8 metres, 3.1 metres, 2.3 metres and 5.6 metres respectively due to the diversion of water from the Churchill River Basin. The Churchill River Diversion has also changed the seasonal timing of water levels and increased the magnitude of water level fluctuations. 4 TABLE OF CONTENTS EXECUTIVE SUMMARY……………………………………………………… 3 TABLE OF CONTENTS ………………………………………………………... 5 INTRODUCTION …………………………………….............…………………. 7 HYDROLOGY ………………………………………………………………….. 8 STUDY METHOD …………………………………………………….……….. 9 MODEL VERIFICATION ……………………….........……………….……….. 13 RESULTS……………………….........……………….………............................. 15 CONCLUSIONS……………………….........……………............….……….. 24 REFERENCES………………...............……….........……………….……….. 27 APPENDICES APPENDIX A –MAPS ……………………………………………………. ......... 29 APPENDIX B – RESULTS ………………………….....……………..…….…… 31 APPENDIX C – RATING CURVES……….......................................................... 37 APPENDIX D – MODEL VERIFICATION ...................……………………...... 50 5 6 INTRODUCTION The following is a report on simulated water levels and river flows for the Rat and Burntwood River systems without the Churchill River Diversion. Simulated water levels and river flows are required to estimate the hydraulic impacts of the Churchill River Diversion for Regional Cumulative Effects Assessment and for other purposes including for operations and resource planning. The Churchill River Diversion has changed the river flow and water level regimes for Rat and Burntwood Rivers. Construction of the Churchill River Diversion began in 1972 and was completed in 1976. The project included the construction of control structures at Missi and Notigi and the excavation of a diversion channel from the South Bay of Southern Indian Lake to Isset Lake and the diversion of water into the Nelson River system via the Rat and Burntwood Rivers. The operation of the Churchill River Diversion influences the water regime of Southern Indian Lake, the Lower Churchill River, the Rat and Burntwood Rivers and the Nelson River. However for the purposes of this report, only the Rat and Burntwood Rivers has been analyzed. Similar analysis for the Churchill and Nelson Rivers is available in separate reports entitled “An Assessment of the Hydraulic Impacts of the Churchill River Diversion on the Upper and Lower Churchill Rivers” 1, and “An Assessment of the Hydraulic Impacts of the Lake Winnipeg Regulation and the Churchill River Diversion on the Nelson River” 2. In this study, a lake routing and water balance spreadsheet model was developed to simulate conditions without the Churchill River Diversion. The simulated results from this model were then compared against historic observations for select periods to assess the hydraulic impacts of the Churchill River Diversion on the Rat and Burntwood Rivers. 7 A study period from 1956 to 2014 was selected because of data availability and the relatively long time period permits maximum flexibility of data usage for Regional Cumulative Effects Assessment and other purposes. Prior to 1956, there is virtually no hydrometric data available for the Rat and Burntwood Rivers. Model results can be used to assess trends and patterns and overall hydraulic characteristics but caution should be exercised when comparing precise day to day results because the model does not explicitly capture localized events such as heavy rain or wind nor does it simulate day to day variations in winter ice conditions that occur. HYDROLOGY The Churchill River originates in northern Alberta and ends at the Hudson Bay near the town of Churchill. The Churchill River has a drainage area of approximately 300,000 square kilometers. The largest lake in the basin, Reindeer Lake, is regulated by Saskpower for power production at Island Falls Generating Station. Prior to the Churchill River Diversion, river flows exited Southern Indian Lake at Missi Falls through two natural outlets at the east end of the lake and flowed down the Lower Churchill River into the Hudson Bay. With the Churchill River Diversion in place approximately 83% of the potential outflow at Missi Falls is diverted down the Rat and Burntwood Rivers for power production purposes on the Lower Nelson River. See map Figures A1 and A2 in Appendix A. Typically, diversion outflows at Notigi Control Structure are set to maximize hydro electric power production from the Kettle, Long Spruce and Limestone Generating Stations. Missi outflows are minimized except when the Churchill and/or Nelson River are in flood and there is water surplus to the needs of the power system. 8 STUDY METHOD In this study, a lake routing and water balance spreadsheet model was developed to simulate hydraulic conditions on the Burntwood River without the Churchill River Diversion. Key features of the model are: it is Excel spreadsheet based; it uses a daily time step and it covers a timeframe from June 25, 1956 to December 31, 2014. This start date was chosen because it coincides with the in service date of the Water Survey of Canada streamflow station on the Burntwood River at Thompson (06TG001) which is the major flow measurement location on the Burntwood River. A hydraulic schematic of the model is shown in Figure 1 below. The model simulates the hydraulic conditions on the Rat and Burntwood Rivers between the site of the Notigi Control Structure and Split Lake. Natural river flows without the Churchill River Diversion are routed past the site of the Notigi Control Structure through Wapisu, Threepoint, Wuskwatim, Opegano, and Birchtree Lakes then past the City of Thompson and to the confluence where the Burntwood River meets Split Lake. Local tributary flow was added along the way to preserve the water balance and maintain hydraulic integrity. Note that this model uses a lake level routing procedure which does not consider channel routing effects or the hydraulic routing of flood waves. A further improvement to