United States Air Force Academy Stream Channel Restoration
Urbanization of areas adjacent to the U.S. Air Force Academy’s eastern boundary has disrupted the function and stability of the stream channels and floodplains contributing to Monument Creek from the east. Increased surface runoff from developed landscapes is producing higher stormwater flow in all of the historically ephemeral streams. These recent hydrologic changes—in combination with highly erodible soils and previously altered stream profiles—have caused serious erosion impacts to the streams and the associated riparian areas, including the habitat of the threatened Preble’s meadow jumping mouse.
Matrix staff previously completed the design for Black Forest Creek, Monument Branch, Middle Tributary, and Elkhorn Creek and is currently in the design process for Kettle Creek, Middle Tributary (east of the Santa Fe Trail), Black Squirrel Creek, and Lehman Run. Design goals consist of providing constructible and stable natural channel designs to restore and sustain the habitat and riparian values of each stream channel on the academy.
Objectives include protecting and enhancing the upland and riparian habitats of the threatened Preble’s meadow jumping mouse; preventing further erosion of the stream channel and the migration of existing headcuts; restoring the stream channel to convey the base flow; and effectively transporting the sediment load. Design components consist of loose and grouted boulder drop structure design in combination with significant earthwork and grading techniques. This methodology focuses on restoring a functional connection between the stream channel and floodplain to help minimize erosive forces from increased stormwater runoff.
Matrix also designed a USBR stepped drop structure to prevent the migration of the existing headcut on Elkhorn Creek, east of I-25, and to transition flood flows released by the upstream detention pond to the restored downstream channel. This drop structure was designed to transition a spectrum of flood flows ranging from the bankfull flood to the 100-yr flood in order to preserve the stability of the downstream channel. The structure was designed to release flood flows (up to the bankfull flood) directly into the bankfull channel while spreading out all larger flood flows onto the adjacent floodplain.
Matrix staff was responsible for providing construction inspection and quality control services for the academy’s implementation of the design plans and specifications for the stream restoration of Elkhorn Creek, Middle Tributary, and Monument Branch. Matrix conducted daily field inspections of construction to confirm that the work was being executed in compliance with the approved contract documents. Weekly written quality control reports and digital photographs of each site inspection were provided to the academy’s project manager, construction inspector, and to the construction contractor. The inspection reports included all observations of construction deficiencies with installed equipment, materials, and workmanship.
- Hydraulic Modeling and Analysis
- Channel Stability Analysis
- River Restoration and Channel Design
- Construction Documents
- Cost Estimating