by F. Yates Oppermann, Environmental Planner, Colorado Department of Transportation

Photo 1:
East Plum Creek as it existed prior to the Conservation Bank Project. Note the exposed sewage pipes.
Photo 2:
Today, the downcutting has been reversed, the water table has risen, and the sewage pipes have been reburied.

In 2001, the Colorado Department of Transportation (CDOT) began planning improvements at bridges over East Plum Creek in Douglas County that would impact habitat for the Preble’s Meadow Jumping Mouse (Zapus hudsonius preblei). In addition to the bridge improvements, several other projects in Douglas County were in their early planning stages and had identified potential impacts on the mouse that would require mitigation. East Plum Creek has seen significant downcutting because of increased development within the drainage. Because of the increase in paved surfaces in the drainage, water from storms that historically seeped into the groundwater now funnel directly into the creek. As a result, the creek was cutting through the sandy soil. As the channel cut deeper, the groundwater table dropped and riparian habitat was dying off. CDOT recognized an opportunity to improve more habitat along the creek than would be necessary to mitigate for impacts from the bridge projects, and began negotiations with the U.S. Fish and Wildlife Service (FWS) and the Federal Highway Administration (FHWA) about creating Colorado’s first conservation bank. A conservation bank is based on a similar premise to a wetland bank: large, connected areas can provide better resource conservation than isolated small areas. Mitigation credit in a conservation bank can be tied to factors relevant to the target species and can be used to offset unavoidable impacts to species within the geographic area.
CDOT proposed an innovative mitigation program to the FWS. By placing a series of check dams along East Plum Creek, CDOT hoped to eliminate the impact of stormwater flow within an area of the creek. To minimize the disturbance of the riparian habitat, the check dams would be vibrated through the sandy soil to the bedrock below, avoiding the need for extensive excavation within the habitat. The check dams would cause the water to slow down, and raise the water table in the adjacent riparian areas. This would allow the riparian habitat to recover and protect vanishing Preble’s mouse habitat. Mitigation credits were tied to success criteria, including vegetation levels and reestablishment of a higher water table. Time was of the essence. In order to minimize impacts to the mouse, construction on the bridges had to be completed during the mouse’s hibernation cycle, roughly November through May. The construction work had to be started soon or work could not be completed before the end of the hibernation cycle. By working closely with the FWS, CDOT and the FHWA were able to reach a handshake agreement on the general conservation bank proposal that allowed the bridge projects to move forward before the agreement was formalized. Success criteria for the bank were tied to several factors, including elevating the water table, and the recovery of the riparian vegetation that provides habitat for the mouse. CDOT’s Executive Director, Tom Norton, signed the final banking agreement before the Transportation Committee on April 17, 2003.
After only a year, significant changes could already be seen within the conservation bank. Instead of further down-cutting, sizable deposition is occurring within the stream channel, the groundwater table throughout the floodplain has risen, and riparian plant life is flourishing. Even during the height of the drought, the water table was elevated to the point where the riparian vegetation began to recover. Even more amazing, mouse populations showed increases within the banking area while populations just outside the bank declined. More recently, biological evaluations have found Iowa darter (Etheostoma exile) within the bank. The Iowa darter is listed by the State of Colorado as a species of concern.
The East Plum Creek conservation bank has exceeded the expectations of all of parties involved. The riparian vegetation has recovered faster than expected, and the biodiversity within the conservation bank has increased as well. People walking along the bike path through the conservation area may see raptors, beaver, kingfisher, and renewed vigor of the riparian vegetation. What visitors won’t see is a sewage line that crossed the creek. Before the check dams were installed, downcutting of the creek had exposed the sewage line to the point that it was actually elevated above the creek instead of buried. The exposed pipe was in danger of rupturing and contaminating the creek. With the installation of the check dams, passive deposition has elevated to streambed back to the point where the sewage line is completely buried and is no longer in danger of collapse.
By working cooperatively, CDOT, FHWA, and the FWS were able to design a conservation bank that not only meets the needs of the various agencies involved, but provides the community with a valuable resource, and the state with an example of how environmental stewardship benefits everyone.
The Colorado Department of Transportation (CDOT) and the Federal Highway Administration (FHWA) take seriously their responsibilities under the Endangered Species Act (ESA) and other environmental laws and regulations. In fulfilling their duties to provide a safe and efficient transportation system, CDOT and FHWA recognize the need to avoid and minimize impacts to environmental resources to the extent possible. Both gencies have also established environmental ethics that promote activities and programs that do more than simply comply with environmental laws and regulations, but support active stewardship of the environment by identifying opportunities to preserve and enhance the environment where possible. Unfortunately, some impacts are unavoidable. CDOT and the Colorado Division of the FHWA recognize that the most environmentally effective way to complete mitigation for unavoidable impacts is through proactive programs that complete mitigation before impacts ever occur. Additionally, proactive environmental programs are more cost effective than traditional project-by-project mitigation.
Proactive environmental programs provide the opportunity to redirect resources to environmental enhancement and restoration instead of administrative paperwork needed to negotiate mitigation requirements for individual transportation projects. Money saved by avoiding costs associated with project delays can be used on projects as opposed to paperwork without sacrificing environmental quality. Proactive environmental programs ensure that mitigation is established before impact, thereby eliminating the environmental degradation gap between when impacts occur and mitigation is successfully completed.

Colorado Riparian Association