Niwot Ditch

Project Information

Niwot Ditch Diversion Reconstruction and Fish Passage Installation Project

Boulder County Parks and Open Space, Colorado Trout Unlimited
Longmont, Boulder County, CO – 2021

Project Owner

Boulder County

Project Amount


Project Date

February 2021 – January 2022

Project References

Tim Zych
Project Manager

Boulder County Parks and Open Space
5201 St. Vrain Rd
Longmont, CO 80508


Lucas Babbitt, PE
Design Engineer

P.O. Box 1609
Salida, CO 81021


About the Project

After the floods in 2013, a historical push-up diversion dam was constructed on a reach of St. Vrain Creek that is one of the last strongholds for native transition zone fish in Colorado and is one of CPW’s highest priorities for native fish conservation in the state. One of the management goals for conservation of these sensitive native fish populations is to restore upstream-downstream connectivity and allow for natural movements of both native and nonnative sport fish by removing instream barriers to movement. The primary goal of this project was to protect and restore native fish populations while ensuring the efficient delivery of decreed water rights. This project replaced the existing diversion dam with two engineered diversion structures, 532 CY of soil riprap, 36” constructed boulder riffle drops, 48” stacked boulder walls, 560 LF of rootwad revetments, 1120 LF coir wrapped soil lifts, 2000 live willow stakes, and 3800 landscape plantings along 1200 LF of stream length. Using design concepts from natural channel design, the new diversion dam was built as a multi-objective structure built from natural materials that is more resilient to high flows, reduces flood risk, allows passage of native and non-native fish, and facilitates natural stream processes and function. This project required a constructed stream bypass, active dewatering, multiple stream crossings, and management of stormwater flows. The project also involved careful coordination and integration of adjacent landowners, private property owners, multiple ditch companies, and numerous stakeholders.