Water Stewardship Information Sources
| ID | 1775 |
|---|---|
| Citation | Tetra Tech EBA. 2014. Lower Mission Creek hydraulic capacity study, Kelowna, BC. Prepared for BC FLNRO |
| Organization | FLNRO |
| URL | http://www.missioncreek.ca/wp-content/uploads/2014/07/Lower-Mission-Creek-Report.pdf |
| Abstract/Description or Keywords | Tetra Tech EBA Inc. (Tetra Tech EBA) was retained by BC Ministry of Forests, Lands and Natural Resource Operations (MFLNRO) to conduct the Lower Mission Creek Hydraulic Capacity study as a result of a proposal submitted on December 17, 2013. The objectives of the study are to determine the 200-year flood profile along the lower reach of Mission Creek in Kelowna, to provide recommendations on adequate dike crest elevations along the existing dike system, to discuss the benefits and practicality of sediment removal, and to determine the impacts of a setback dike on the recommended dike crest elevations. Mission Creek is located in the western portion of the Okanagan Highland and is the largest tributary of Okanagan Lake. The total direct drainage area at the mouth of Mission Creek is approximately 850 km2 . The lowest reaches of Mission Creek flow through the City of Kelowna, and are partially contained on both banks by an existing dike system. There are six bridge crossings located along the study reach: Lakeshore Road Bridge, Gordon Drive Bridge, Casorso Road Bridge, KLO Road Bridge and two pedestrian bridges located about 7 km and 8 km upstream from the creek mouth. The right bank dike system (looking downstream) extends from just upstream of Lakeshore Road Bridge to Ziprick Road, for a total length of 7.5 km. The left bank dike system (looking downstream) starts from about 200 m upstream of Lakeshore Road Bridge to Casorso Road Bridge and starts again from 1.1 km upstream of Casorso Road Bridge to about 1 km upstream of KLO Road Bridge. A total of 84 creek cross sections along Mission Creek from Okanagan Lake to about 500 m upstream of Ziprick Road were surveyed within the study reach. Most of the cross section locations were based on the previous surveys completed by the Province in 1983 and 1992 as part of the Mission Creek floodplain mapping. Surveying of the cross sections that intersect with the proposed setback dike alignment downstream of Casorso Road Bridge were extended to cover the potential floodplain areas. A flood frequency analysis using the available historical peak flow at the Mission Creek near East Kelowna hydrometric station (08NM116) was carried out. The recommended 200-year maximum instantaneous and maximum daily flows for the upstream end of the study reach were determined to be 137 m3 /s and 112 m3 /s, respectively. The recommended 200-year maximum instantaneous and maximum daily flows for the reach downstream of Casorso Road Bridge were determined to be 144 m3 /s and 118 m3 /s, respectively. Such peak flow estimates include a factor of 10% to take into account impacts of climate change on the hydrology of Mission Creek. In view of the 12% increase in peak flows in Mission Creek over the last 10 years, likely due to the combination of climate change, natural variability, and forest cover removal by forest fires, logging activities and beetle infestation, it is also recommended that a sensitivity analysis using a combined factor ranging from 10% to 22% be carried out in future hydraulic analyses such that the incremental difference in water levels can be determined and discussed. A hydraulic model of the Lower Mission Creek was developed based on the survey conducted for the current assignment, and both steady and unsteady flow analyses were performed. Four model scenarios were developed and analyzed, and five lake levels were used as the downstream boundary conditions as suggested in the terms of reference. Based on the resulting water profiles from the hydraulic model, critical dike sections with inadequate freeboard were identified for all scenarios. Critical dike sections were identified along the lower portions of the study reach between Lakeshore Road Bridge and KLO Road Bridge. With the assumption that the proposed Lakeshore Road Bridge will be in place in the near future, the recommended dike crest elevations along the critical dike sections were determined from the unsteady flow analysis results for the model with the proposed Lakeshore Road Bridge in place with the full pool target lake level as the downstream boundary condition. In general, a maximum raise of 0.5 m is required on the right dike at XS-11 upstream of Gordon Drive Bridge and an average raise of 0.2 m is required all the critical sections along the right dike. A maximum raise of 0.4 m is required on the left dike at XS-19 just downstream of Casorso Road Bridge and an average raise of 0.16 m is required for all the critical sections along the left dike. Model results of the sediment removal scenario indicate that sediment removal would significantly reduce water levels by a maximum of 0.5 m and an average of about 0.2 m along the reach between Lakeshore Road Bridge and KLO Road Bridge. A rough comparison of the 1983/1992 channel survey and the 2014 channel survey was also conducted to determine the change of channel bed over the last 20 to 30 years in general. Based on the model results and a comparison of the 1983/1992 and 2014 channel surveys, it is recommended that sediment removal along the study reach be further considered as part of the dike maintenance plan. However, raising the dike in critical sections would still be a viable solution to ensure adequate hydraulic capacity in Lower Mission Creek. Model results of the setback dike scenario show that the proposed setback dike would slightly reduce water level by a maximum of 0.24 m and an average of about 0.05 m along the reach between the downstream end of the proposed setback dike and XS-26, located about 700 m upstream of Casorso Road Bridge. In addition, it should be noted that the resulting flow velocities in the vicinity of the proposed setback dike alignment are considerably reduced. Such reduced flow velocities will likely allow more sediment to settle in this local reach, and it is recommended that during the design of the proposed setback dike, additional freeboard should be considered to account for the long term aggradation, which could be determined by analyzing historical channel cross sections. |
| Information Type | report |
| Regional Watershed | Okanagan |
| Sub-watershed if known | Mission Creek |
| Aquifer # | 461; 463; 464; 467; 473 |
| Comments | |
| Project status | complete |
| Contact Name | Maria Lau |
| Contact Email | [email protected] |