The first consideration for preventing flooding and erosion from stormwater runoff in this upscale and sustainability-minded com- munity was how to protect the environment, especially the tributaries that provided the project’s name – Five Creeks. The design team at InterCAD Services, Ltd. (Vancouver, B.C.) found a way to maintain low level flows in the creeks. This would maintain the environmental benefits of the creek while diverting only the excess flows that would occur during heavy rain storms, and could have caused damage to the creeks, property and downstream infrastructure. “During the past 100 or 150 years, as the downstream neighbourhoods have developed, people have created various pinch points,” explained Iain Lowe, InterCAD principal and the project manager. “So, there was a realization that there was a need to divert water away from the creeks to protect the downstream lands. We devised a system to take a large volume of water of about 30,000 litres (1,000 cubic feet) a second out of the creeks and divert it directly to the ocean.” Once completed, the new system will serve the Pipe, Westmount, Cave, Godman, and Turner watersheds by directing creek flow that would potentially overflow the banks of the creeks and flood the area into the new pipe. The Five Creeks Stormwater Flood Projection Proj - ect was initiated and substantially funded by developer British Pacific Properties (BPP) in a partnership with West Vancouver as a way to protect the area. In 2013, the District of West Vancouver prepared an Integrated Storm - water Management Plan (ISMP) to address concerns of overland flood - ing within the Five Creeks watershed area. The plan would benefit both existing and future neighborhoods below and above the Upper Levels Highway. It called for a stormwater pipe to run through the Westmount and West Bay neighborhoods from the Upper Levels Highway down to the Burrard Inlet at the foot of 31st Street. Intake structures installed within the creeks would divert stormwater from larger, infrequent rain events into the pipe, while retaining base flows within the creeks. Now, some 2,000 meters (6,500 feet) of the buried stormwater pipe runs under the roads through the Westmount and West Bay neighbor- hoods from north of the Upper Levels Highway down to the Burrard Inlet at the foot of 31st Street. The Main Leg of the storm sewer used 800m of 1,500mm diameter (2,625 feet of 60-inch diameter) ADS SaniTite® HP pipe with fabricated bends, tees and manholes and 400m of 1,800mm diameter (1,300 feet of 72-inch diameter) concrete pipe. PRECISE PIPELINE DESIGN PROVIDES STORMWATER RUNOFF CONTROL TO PROTECT WEST VANCOUVER New Pipeline Fights Flooding and Erosion in a Growing Region
More than 2,000 meters of 1500mm SaniTite HP pipe from ADS was used in the Five Creeks Stormwater Flood Projection Project. Photo: ADS
Being implemented in stages, the second phase, the East Leg, is sched - uled to be completed by early 2022 and will use 1,200m (3,900 ft) of 900mm to 1,500mm (36 to 60 in) diameter SaniTite HP pipe. The final phase, the West Leg, will extend the pipe to the northwest to pick up flows from Turner and Godman Creeks. “While BPP is developing the lands north of the Highway, the ISMP recognizes that the construction of the developments will result in neg- ligible increases in runoff in the post-development condition.” Lowe said. “The way it works is that all the flows up to a two-year event remain in the creeks, so we don’t touch any of that water. Any water flowing above that two-year level is progressively split off so that at the end of the day we essentially end up with a 50/50 split between the creek and the diversion pipe. The pipeline is designed to function up to a 200-year storm. The new stormwater pipe will address concerns related to flooding and erosion by diverting excess stormwater out of the creeks during extreme weather events, safely conveying the flow into the ocean. Photo: ADS
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july 2021
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