New Pipeline Fights Flooding and Erosion in a Growing Region
The first consideration for preventing flooding and erosion from stormwater runoff in this upscale and sustainability-minded community 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 Project 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 Stormwater Management Plan (ISMP) to address concerns of overland flooding 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 neighborhoods 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. Being implemented in stages, the second phase, the East Leg, is scheduled 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 negligible 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.
“We obviously didn’t want to dry out these creeks, and it was important to maintain the environmental benefits of those creeks. Essentially, we removed the large rain events from the creek, which provides protection to the downstream properties and an area of around 500 acres containing numerous homes.”
Maximizing the hydraulic efficiency of the pipe conveying the diverted water was a key in selecting the type of pipe that would be used. Lowe’s plan called for pipe in diameters from 1500mm to 1800mm (60 to 72 in) to accommodate the volume of runoff. He first considered using all reinforced concrete pipe (RCP). In order to meet the hydraulic design consideration, however, there was a desire for it to be would lined, in order to provide protection against abrasion which would add to the cost.
“As we designed the alignment and calculated the hydraulic need for conveying gravity flow runoff down the steep grade from the base of Cypress Mountain all the way to the Pacific, that led us to thinking about thermoplastic types of pipe,” he explained. “SaniTite only goes up to 1500mm diameter. At some points we needed 1800mm diameter pipe. So, we couldn’t use it for all the run, but we reached a compromise. The reason we went with it was because the pipe provides excellent hydraulics, being so smooth on the inside, plus it’s also very durable as well, so it is resistant to operational damage from any sediment that enters the pipe. Our materials selection was acceptable to the District of West Vancouver.”
Previous to the Five Creeks project, ADS submitted its SaniTite HP polypropylene pipe to the Master Municipal Construction Documents Association, Civil Committee, which unanimously approved it and material and added the pipe to the Master Municipal Construction Documents (MMCD) list of approved products for use in highway, culvert and other infrastructure projects in British Columbia. The listings for polypropylene pipe can be found in MMCD Section 33 40 01: Storm Sewers, Mainline Profile and in Section 33 42 13: Pipe Culverts, Open Profile.
ADS SaniTite HP polypropylene pipe is certified to meet CSA Standard B182.13 by Intertek, a third-party certification body authorized by the Standards Council of Canada (SCC) to certify products. Additionally, the structural performance of SaniTite HP has been evaluated in accordance with American Association of State Highway and Transportation Officials (AASHTO) Load Resistance Factor Design (LRFD) Bridge Design Specifications. SaniTite HP is accepted by the British Columbia and Ontario Ministries of Transportation (BCMOT and MTO), the Ontario Provincial Standards (OPS) and meets ASTM F2764 with 100 kPa (15psi) joints tested in accordance with ASTM D3212 for water tightness.
Installation of the new pipeline was done by Complete Utility Contractors Ltd. (Pitt Meadows, B.C.) with a crew of four to seven. “To get through the bedrock, we had two excavators with large hoe ram attachments, but we did have to blast in some areas,” said Adam Matheos, project manager for Complete Utility Contractors. “We laid in the pipe sections concurrently. We excavated and didn’t get too far ahead so the pipe would line up. And because the ADS pipe is lighter than the concrete and comes in longer sections, it definitely made for a quicker installation. There were fewer joints and it was easier to put into the ground and push together. This made it much easier going through residential areas at a pretty significant grade and we were anywhere from three to four meters deep. Naturally, the bedrock was more challenging but even though this was our first time using the ADS pipe in such large diameters, it was easy to work with and very durable.”
The pipe came from the ADS plant with special five-degree mitres for some sections. “Those five-degree bends were needed for constructing the pipe around within the existing roads, and for running between existing underground utilities and services,” stated Lowe. “We tried to create smooth circular radius curves or bends which we achieved using the SaniTite.” Specific sections of the pipe were fabricated at the ADS plant to include a riser with a ladder inside to act as a manhole.
In addition to the new stormwater management system, the project will also include the relocation of water mains, complete reconstruction of roads and resurfacing and the addition of sidewalks.
When completed, the project will increase the level of flood protection for homes below the Upper Levels Highway. Rerouting the excess stormwater will also reduce erosion, help to safeguard residents and property while accomplishing its original goal of protecting the watershed health of the Five Creek drainage areas.
Additional information about ADS can be found at: www.adspipe.com.