Just released by RDOS – a study done by Ecora Engineering of Penticton
Read the complete document for an overall view of Okanagan River to Twin Lakes
Below – One set of recommendations for one section of the system – Hwy 97 (Tomlin to Secrest)
Recommended 2019 flood response actions for Study Area 2 includes:
1. A late winter assessment by Ecora and Dobson Engineering to review MoTI temporary works constructed in 2018 for their potential to increase flooding of adjacent properties. Recommendations will be provided, if necessary, for removal or modification of these temporary works.
2. Installation of 700 lineal meters of 36” tiger dams, prior to the 2019 spring freshet, to protect low-lying private properties on both sides of the creek. Access to dwellings could be maintained by installing road crush berms (or similar well-draining, drivable material) to an equivalent height and alignment to the tiger dam and sloped to allow vehicular traffic.
3. Two temporary accesses were installed on 296 and 322 Sportsmen’s Bowl Road which were designed to fail in a flood event. A swale was designed to allow floodwater to overtop the road fill and make its way back into the creek should flows exceed the culvert capacity. These swales have since been leveled off which poses a risk to downstream properties since floodwaters could develop new flow paths and/or channels through downstream properties instead of flowing through the creek channel. These accesses need to be modified to re-establish the flood swale to allow for a controlled failure prior to the 2019 freshet. If extreme flows should occur in 2019, these driveway culverts should be removed to restore full channel capacity until the freshet passes.
Park Rill Creek 2019 Flood Response Recommendations File No: CP-18-568-RDO | November 2018
Kelowna | Penticton | Prince George | Vancouver | Victoria | Chilliwack 4
4. As an extension of the monitoring at Highway 97, once the trigger point has been reached where the upstream end of the culverts at Highway 97 have been submerged, weekly inspections should be completed by a contractor to monitor water levels and remove private culvert crossings as required to increase flow capacity. Frequency of inspections should be increased to daily once the two 800 mmØ emergency overflow culverts under Highway 97 are in service.
5. Identify an area upstream of the Highway 97 ditch, between Sportsmen’s Bowl Road and the Highway where a sediment catchment area (approximately 500 m2) can be excavated. This area would allow coarse sediment to settle out prior to discharging through the culverts and minimize the accumulation of sediment in areas where access is difficult.
6. Ecora will complete a stability, erosion and debris assessment of the Park Rill Creek channel between the Southern Okanagan Sportsmen’s Association property and Secrest Hill Road to determine if there are any unknown risks in this area that could trigger a debris flow and provide any necessary response recommendations.
7. Secrest Hill Road is a risk to public safety. If the culverts are not replaced by MoTI, it is recommended that this crossing be monitored daily for signs of seepage and piping failure once the culvert inlets are submerged, as the consequence of failure includes the likely loss of life for downstream residents. If the crossing is upgraded, an understanding of the maximum flows that could occur through the upgraded crossing should be quantified to be included in the response plan as part of the late winter assessment identified in the first bullet. The potential for increased peak flows in the lower system has increased due to upgrades to most of the upstream crossings, which has removed the attenuation of peak flows in the system that was present in 2018 due to undersized culverts.
In Spring 2018, the Park Rill Creek watershed experienced extensive flooding with the most heavily impacted areas being the Willowbrook area, Sportsmens Bowl Road area and properties along the stream channel downstream of Highway 97 to the confluence with the Okanagan River. The flooding caused damage to homes, public infrastructure, loss of property and numerous evacuations. The emergency response required an extensive effort to prevent floodwaters from damaging homes and overtopping public roads, most notably Secrest Hill Road nearly overtopped presenting a serious risk to public safety which required the mobilization of two emergency 8” pumps and the installation of an 800mm overflow pipe to prevent future risks of overtopping. As part of the emergency response works, the Ministry of Transportation and Infrastructure (MoTI) installed two 800mmØ culverts across Highway 97 to increase flow capacity downstream and the RDOS Emergency Operations Center (EOC) coordinated the mobilization pumps at the Park Rill Creek outlet to discharge water into the Okanagan River. Flooding in the Park Rill area resulted in considerable expenditure for pumping and temporary flood protection works, implemented by the RDOS EOC and funded by Emergency Management BC (EMBC).
Repeated flooding of infrastructure in the Park Rill Creek watershed has been documented since the 1950’s (Botham 1973).