In September 2013, the Front Range of Colorado experienced a historic and devastating 100‐year flood that resulted in damage to numerous roads and state highways. During that event and the 2015 heavy rain event, the Monument Branch culverts (under Interstate 25), foundations, and wingwalls were damaged. Within Monument Branch, flood and heavy rain events scoured the bed and banks of the waterway, resulting in large deposits of sand, gravel, rock, and concrete debris and loss of natural vegetation. The Monument Branch Project area is located in El Paso County, and the US Air Force owns the entire property in this area, with I-25 located within an easement. To permanently improve channel stability and repair the existing I-25 culverts, the project team completed the following improvements:
- To slow velocity of water, and therefore sediment load, entering Monument Creek, five drop structures and drop basins with boulder sills were installed in the Monument Branch channel.
- To mitigate for the significant erosion and additional sediment load that occurred as a result of two scour channels present in the median, the main flows of the drainages were piped and regraded to create swales for surface flows.
- Culvert stabilization consisted of backfilling the headcutting present onsite, adding a concrete apron to prevent any additional headcutting, and reattaching wingwalls.