Stormwater Pipeline Design

The City of Cheyenne had a stormwater system that was too small to handle heavy rain, which often led to flooding, especially along Pershing Boulevard and nearby intersections. To fix this, Trihydro designed a new stormwater pipeline that connected an upgraded drainage system to an existing pipe.

Trihydro designed a new 850-foot-long stormwater pipeline along Snyder Avenue that connects an upgraded drainage system on Pershing Boulevard to an existing pipe near the intersection of Snyder and Randall Avenue.

Connecting Old and New Pipes

One of the biggest challenges was that the new 48-inch pipe had to connect to an older, smaller 36-inch pipe that drains into Crow Creek. Since the older pipe couldn’t handle the increased water flow yet, and a full upgrade wasn’t scheduled until a future project, Trihydro designed special restrictor plates. These restrictor plates were installed in manholes along the new pipe to slow down the water and temporarily store it, preventing flooding. Once the older pipe is upgraded, the restrictor plates can be removed to allow full water flow.

Rerouting Water and Sewer Lines

Another challenge was fitting the large pipe into a narrow, two-lane street already crowded with other utilities. The team had to carefully reroute or work around existing water and sewer lines. In one tricky section, the stormwater pipe had to pass under a 30-inch water main and a 12-inch sewer main. To do this, engineers designed special vaults that temporarily split the large pipe into four smaller ones before reconnecting it.

In areas where there wasn’t enough space to keep the stormwater pipe far enough from drinking water lines, the team proposed using a new type of pipe, Steel Reinforced Polyethylene (SRPE), with pressure-rated joints. This was the first time SRPE was used in Cheyenne, and it worked so well that the City has since used it in other projects.