The Boxelder Watershed

History of Watershed Improvement
Corrected Chris Mason Farm 1904 flood FCMOD H06526

Larimer Co. flood 1904

Credit: Fort Collins Museum of Discovery H06526


Buckhorn flood 1951

Credit: Fort Collins Museum of Discovery lcdpb20


Boxelder Creek Rd. 1967 flood

Credit: Fort Collins Museum of Discovery c01302


Like many creeks in Colorado, Boxelder Creek and its tributaries have both a history of flooding and a history of Coloradoans doing something to control the flooding.

The semi-arid climate of the basin is characterized by unevenly distributed precipitation. Significant short-duration and longer-duration rain events take place frequently.

Two recent local examples similar to past events are the intense, localized rain that caused the Spring Creek flood in Fort Collins in 1997 and the multi-day intense rain that caused widespread flooding in Larimer County in September 2013.

In the 65 years from 1904 to 1969, according to the Soil Conservation Service, 24 major storms and numerous intense local storms produced damaging floods somewhere in the watershed every one to three years.

The farms, ranches, towns, and cities that developed throughout the Boxelder basin during this same time period experienced repeated damage.

Floodwater, sediment, and erosion damaged agricultural land, crops, irrigation facilities, farm and ranch buildings, residential and public structures, roads and highways, and embankments and bridges.

1971 Work Plan Cover

In 1970, after several years of data collection, analysis, and public discussion, a group of concerned citizens, local government leaders, and state and federal agency staff took a major step toward controlling the repeated flooding. They completed the Boxelder Creek Watershed Project Plan.

The project objective was to “reduce damages to agricultural land and crops, irrigation facilities, farmsteads, highways, embankments, and bridges from 10-year frequency storms or larger and to the town of Wellington from the 100-year frequency storms.”

Watershed improvements described in the project plan included land treatment measures, to be carried out by land owners and operators of private and state land, and structural measures. The structural measures to be installed included five single-purpose floodwater detention dams, known today as dams B-2, B-3, B-4, B-5, and B-6.

The project sponsors, providing leadership for the completion of the plan, were the Fort Collins Soil Conservation District and West Greeley Soil Conservation District in Colorado; the Frontier Soil and Water Conservation District and Laramie Rivers Soil and Water Conservation District in Wyoming; the Larimer County Board of Commissioners; the North Poudre Irrigation Company (NPIC); and the Colorado State Soil Conservation Board.

The USDA Soil Conservation Service (now known as the Natural Resources Conservation Service, NRCS) and other state and federal agencies, provided technical assistance for the plan.


Between 1977 and 1982, the five Boxelder dams were constructed, using funds provided by the NRCS under the authority of the 1953 Watershed Protection and Flood Prevention Act.

NPIC, as an original sponsor of the Boxelder Creek Watershed Project, assisted with acquisition of land rights and water rights clearances in preparation for building the dams. Under an agreement with NRCS, the company has operated and maintained the dams since their completion.

Boxelder Creek 100-Year Floodplain

Boundaries, channels, inundation

In 2006, the Federal Emergency Management Agency (FEMA) adopted a revised 100-year floodplain map for the lower Boxelder Basin. In response, regional entities came together to jointly plan flood mitigation improvements.

In 2008, the Boxelder Creek Regional Stormwater Authority was formed by an intergovernmental agreement between the City of Fort Collins, the Town of Wellington, and Larimer County.

In 2009, NPIC received approval for partial NRCS funding to investigate the rehabilitation of dams B-2, B-3, and B-4, with support from the original Boxelder Watershed project sponsors.

NRCS completed updated dam breach evaluations in March 2009 (for dam B-2) and in January 2011 (for dam B-3). In August 2010, NRCS completed Probable Maximum Flood evaluations for dams B-2 and B-3.

Using this and other data, NRCS reviewed the hazard classification of the Boxelder Watershed dams in January 2011. (These reviews take place about every five years for watershed project dams in the U.S.)

The review recommended that the hazard class of dams B-2 and B-3 should be increased from significant to high.

Project sponsors met in March 2011 and expressed support for NPIC’s application for funding to investigate the rehabilitation of dams B-2, B-3, and B-4.

In July 2013, the State of Colorado Division of Water Resources officially changed the hazard classifications of dams B-2 and B-3 from significant to high.

In 2014, NRCS and NPIC agreed on funding for dam rehabilitation planning studies.

In May 2015, the Boxelder Watershed planning study began. The first document produced is the May 2015 Purpose and Need Statement.