| Abstract/Description or Keywords |
The Hydrology Technical Data Report presents background information, methods, and results of baseline hydrological studies conducted for the proposed Prince Rupert Gas Transmission (PRGT) Project. The hydrological technical studies include a review of existing information and data sources and an evaluation of hydrologic conditions pertinent to describe the approximately 1,200 watercourses crossed by the Project. The information and analyses presented in the Technical Data Report are used for Environmental Assessment purposes and more specifically to support the aquatics discipline in the evaluation of watercourse crossing characteristics. The main product of this baseline study is therefore the estimation of flow statistics for the approximately 1,200 ungauged watercourse crossings along the proposed project alignment. Derived flow statistics for each proposed watercourse crossing include mean monthly flows, the mean of maximum daily mean flows by month, and the 2 year, 5 year, and 10 year return period maximum daily mean flows. Flow records are not available for any of the proposed watercourse crossings. As a result, a regional analysis was conducted to derive these flow statistics. Hydrologic zones are areas of generally homogenous hydrologic characteristics. Existing literature regarding hydrologic zones was used to support the understanding of baseline flow characteristics along the pipeline route. Four hydrologic zones were used for this study and include; from east to west, Southern Rocky Mountain Foothills, Nechako Plateau, Northern, and Coastal. For each of hydrologic zone, the regional analysis further required the development of relationships between watershed area and calculated Water Survey of Canada (WSC) flow statistics. Within 150 km of the project and within the project hydrologic zones, 39 WSC hydrometric stations were selected for this purpose. Ungauged proposed project watercourse crossing locations were identified using Terrain Resource Information Management (TRIM) topographical information. The watershed areas associated with these stream crossings were then delineated and measured using the TRIM and CanVec topographical information, using a combination of automated (Green Kenue software) and manual techniques. By applying watershed areas for the ungauged crossings to the relationships developed for representative hydrologic zones, estimates of flow statistics for the ungauged locations were derived. Four of the streams with proposed watercourse crossings are gauged by the WSC either upstream or downstream of proposed project crossings. This information and a watershed scaling method were used to estimate flow statistics at the project crossing, where specific conditions were satisfied. Flow statistics at four proposed project watercourse crossings were generated using this method. Estimated hydrological conditions are variable along the project route. Annual runoff rates range from lows of 200 mm in the Southern Rocky Mountain Foothills and Nechako Plateau to highs of 1,400 mm and 4,000 mm in the Northern and Coastal hydrologic zones. Annual high flows along the project route typically occur during spring freshet. However, as an exception, relatively small watercourses in the Coastal hydrologic zone typically exhibit annual high flows in November due to autumn rain events. Historic ice cover records at the representative WSC hydrometric stations were examined for the earliest and latest freeze-up and break-up dates on record to provide an indication of historic ice coverage that may be anticipated at project watercourse crossings. Surface water licenses in the vicinity of the Project are identified based on information gathered from the British Columbia Ministry of Forests, Lands, and Natural Resources Operations. |
