Boxelder Basin Regional Stormwater Authority

The Boxelder Creek Watershed is a vast, relatively undeveloped area in northeast Larimer County. The drainage basins in this watershed cover approximately 260 square miles and extend from extreme southeast Wyoming into southeast Fort Collins with flooding continuing to extend past Timnath toward the southeast. The Lower Boxelder Valley is irrigated, and it contains some of the best agricultural land in the county.

The Lower Boxelder Basin, close to I-25, has developed into an agribusiness and agriresearch corridor, which includes a major brewery; the Colorado State University Horticultural Research Center; and the Colorado State University Agricultural Research, Development, and Educational Center.

The entire Town of Wellington and a sizeable portion of the City of Fort Collins are included in the Lower Boxelder Basin. The lower, southern portion of the Basin is more urbanized and is impacted by many existing man-made structures, such as streets and buildings.

Historic Flooding

Boxelder Creek and its tributaries have a long history of flooding. A Soil Conservation Service report documents that in a 65-year period from 1904 to 1969, there was a damaging flood every one to three years, on average, somewhere in the watershed. In addition to the 24 major storm events documented within this timeframe, there were numerous localized storms occurring over the irrigated land causing flooding and sediment and erosion damages as well.

In 1947, the Coloradoan newspaper headline read, “Violent Rainstorm Floods Large Area; Crop Losses Heavy.” In this storm, as much as five inches of rain fell northwest of Wellington, damaging nearly 1,000 acres of grain, alfalfa, and corn as well as washing out bridges.

Index

In 1967, heavy rains again flooded the area, causing Boxelder Creek to overtop roads, which resulted in the death of a mother and her three daughters on a county road southeast of Wellington. Seven times that summer, county bridges in the Watershed were destroyed by flooding.

Need for Improvements to Mitigate Flood Hazards

Since 1976, the Boxelder Creek Watershed, along with other parts of Larimer County, has been included in the National Flood Insurance Program. As part of that program, Larimer County, the Town of Wellington, and the City of Fort Collins are required to regulate land uses that exist within the designated floodplains of each respective community. More than 5,000 acres of land in the Lower Boxelder Creek Watershed are designated as floodplains by FEMA.

Owners of buildings within flood hazard areas are required to purchase flood insurance. For individuals, this means that if their house is in a FEMA-designated floodplain, they must purchase flood insurance, which has become quite expensive in recent years. With approximately 5,000 acres of this watershed now identified by FEMA as floodplain, this is a significant issue for many residents.

Potential Flood Damages

Flooding affects everyone, not just the residents directly located in a floodplain. In the event of a flood on Boxelder Creek, or its tributaries, the following may occur:

1. Roadway overtopping.

2. Flood damage to stream crossings.

3. Water supply contamination.

4. Sanitary sewer system disruption by overloading.

5. Disruption of emergency services due to impassable roads.

6. Damages to schools, homes, and businesses.

7. Loss of use of schools, homes, and businesses.

8. Disruption of traffic.

In addition to the hundreds of homes located within the floodplain are two schools, two gas stations, a liquid propane storage facility, numerous business and commercial facilities, sanitary sewers, electrical lines, water transmission lines and other critical infrastructure that could be impacted or damaged by flooding from Boxelder Creek and its tributaries. Access to an electrical substation could be cut off in a major storm, and four major irrigation canals and 30 roads will overtop and be damaged during a 100-year flood.

Often, in times of emergencies, schools are used as an emergency shelter and gathering point. With this issue in mind, two of the three schools in Wellington are in locations subject to flooding.

FEMA-Adopted Study of Boxelder Creek and Its Tributaries

In late 2006, the Federal Emergency Management Agency (FEMA) adopted a revised floodplain map for the Lower Boxelder Basin. The revised floodplain maps were based on a hydrologic study of the Boxelder Watershed produced by Anderson Consulting Engineers in 2001. The revised study takes into account the existence of the SCS Flood Control Dams that were constructed in the late 60s and early 70s as part of the Boxelder Watershed Project. The revised hydrologic study of the Watershed was based on rainfall standards for the area that were prepared and adopted by Larimer County, the Town of Wellington, and the City of Fort Collins.

Addressing the Need

Early in 2005, stormwater planners in northern Larimer County took a holistic approach to addressing flood hazard and stormwater drainage problems in the Boxelder Creek watershed. This watershed, or basin, encompasses over 265 square miles and extends from just north of the Wyoming border to the Poudre River on the south to just below the existing NRCS dams to the north as shown on the entire FEMA Mapped Boxelder Creek Floodplain. Because the Boxelder Creek Floodplain affects many property owners and several local governments, intensive efforts were made to develop a regional flood hazard mitigation plan. It should be noted that Coal Creek and Indian Creek both feed into Boxelder Creek near the Town of Wellington. The communities of Fort Collins, Wellington, Timnath, and Windsor and Larimer County all shared a common goal in mitigating the flood hazard posed by Boxelder Creek. The Alliance was formed in early 2005 with the goal of developing “regional” solutions that would be more efficient and cost-effective than the entities could develop independently.

The Alliance members included:

Colorado Department of Transportation (CDOT)

Larimer County

City of Fort Collins

Town of Wellington

Town of Timnath

Town of Windsor

North Poudre Irrigation Company

Boxelder Sanitation District

New Cache la Poudre Irrigation Company

A Private Property Owners’ Group

Colorado Water Conservation Board (CWCB)

Representatives of these entities met over a period of two years to consider ways to mitigate flood hazards within the area that is tributary to Boxelder Creek from County Road 70 north of Wellington south to where Boxelder Creek floodwaters join Cache la Poudre River. It was determined the best approach to basinwide flood hazard mitigation would be to prepare a common plan for flood mitigation improvements within the basin. Members of the Alliance pooled funding to prepare a storm water Master Plan for the Boxelder Basin. The resulting Boxelder Creek Regional Stormwater Master Plan (Master Plan) was completed in October 2006. This Master Plan formed the basis for the formation of the Boxelder Basin Regional Stormwater Authority (Authority). The components and intent of this Master Plan are explained further under the Project and Agreements section of this website.

The Authority was formed by an Intergovernmental Agreement (IGA) in August of 2008 by its Member Entities—the City of Fort Collins, the Town of Wellington, and Larimer County. This IGA also established the Boxelder Authority Boundary. Residences and businesses within this boundary are assessed a drainage fee based on an average or calculated impervious surface area within their property. These fees are then used to develop and construct the regional drainage improvement projects and manage the Authority. The central purpose of the Authority, identified in the IGA, was to develop and construct Regional Drainage Projects. The three projects preliminarily identified in the 2006 Master Plan are as follows:

The Coal Creek Flood Mitigation Project.

Edson Reservoir.

The Middle Basin Improvements.

Implementation

The first of these regional improvement projects, the Coal Creek Flood Mitigation Project, has recently been completed by the Authority in cooperation with Larimer County. The purpose of the project was to protect close to 200 homes, dozens of businesses, and two schools that were within the Coal Creek floodplain in the Town of Wellington. This $5.1M project diverts stormwater flows from Coal Creek (which is tributary to Boxelder Creek) into the Clark Reservoir Inlet Canal and ultimately into Clark Reservoir. North Poudre Irrigation Company (NPIC) owns these facilities, which are north of the Town of Wellington. The Inlet Canal was enlarged to accommodate the 1,700cfs from Coal Creek, Clark Reservoir was dredged, and the emergency spillway was raised to accommodate the decreed storage of NPIC along with the diverted Coal Creek flows. During construction, 186,000 cubic yards of sediment was removed from Clark Reservoir. The dredging, combined with raising the emergency spillway, provided the 540 acre-feet of flood storage along with the 871 acre-feet of decreed storage for NPIC. Funding for this project came from a FEMA Pre-Disaster Mitigation Grant (PDM), matching funds, and Authority Service Fees.

The second regional improvement project identified in the Master Plan was originally called Edson Reservoir. This dry stormwater detention reservoir was only preliminarily sized (660 to 990 acre-feet) and cited in the Master Plan. When design efforts became more focused and detailed, subsequent to the Master Plan, this original site for this facility proved to be unfeasible. This was due to the limited storage capacity at this site and the fact that reservoir ponding would inundate seven existing home sites. As a result of this determination, a detailed Siting Study was completed by Ayres Associates in May 2010 to determine the most advantageous site to relocate the Edson project, taking into account flood reduction, cost, and constructability issues. This Siting Study evaluated over seven different sites for this facility. As a result of this study, additional discussions were held with Colorado State University Research Foundation (CSURF) about the ARDEC site (North of CR56) and with the City of Thornton regarding their site (south of CR56). When these discussions led to no feasible solutions, the Authority moved forward in evaluating the site immediately adjacent to the Gray Lakes Reservoirs, owned by the Lake Canal Reservoir Company. Eventually this site was deemed to be the most cost-effective solution and became the East Side Detention Facility (ESDF). After discussions with the State Engineer and the completion of a fatal flaw analysis, the Authority moved forward with final design and secured a loan with the Colorado Water Conservation Board.

The third project, the Middle Basin Improvements, went through a metamorphosis as well. Originally identified in the Master Plan as principally two storm drainage channels between County Road 54 and County Road 52 and a siphon structure at the crossing of Boxelder Creek and the Larimer and Weld Canal, the improvements were reduced in scope and refined in design. Most of this change in the scope of the improvements had to do with the eventual size and location of the East Side Detention Facility (ESDF), which will greatly reduce the Boxelder 100-year flows where they cross the Larimer and Weld Canal. As a result, these improvements have now been reduced to a single side-flow spillway structure known as the Larimer and Weld Canal Crossing Structure (LWCCS) at the crossing of Boxelder Creek and the Larimer and Weld Canal.