The scope of this Project includes completing a FHAD for the Weir Gulch watershed, which includes the 1st Avenue Tributary, to be consistent with current UDFCD and local criteria. The MDP consists of three phases, culminating in a final major drainageway Conceptual Design Report.
The Weir Gulch watershed was one of the first watersheds to be master planned after the formation of the UDFCD in 1969. The original MDP for the Weir Gulch watershed is titled Major Drainageway Planning, Sanderson Gulch/Weir Gulch (Frasier & Gingery, August 1972) (1972 MDP). A FHAD was not completed for Weir Gulch after the original MDP was completed. However, the peak flows that are published in the 1972 MDP were used to develop the original Flood Insurance Rate Map (FIRM) and have been used for planning and design purposes.
The 1972 MDP was completed at a time when UDFCD was still modifying rainfall criteria and the Colorado Urban Hydrograph Procedure (CUHP) had not been developed. UDFCD has since established different rainfall criterion that supersedes what was used in the 1972 MDP and uses the CUHP as the model that best represents the rainfall/runoff relationship in the Denver metro area. Additionally, better impervious data is now available, than what was available at the time of the 1972 MDP, that more accurately quantifies the imperviousness associated with different land use conditions. All of these factors will likely result in increased peak flows throughout the watershed when evaluated with current hydrologic modeling software. As a result, an update to the FHAD for the Weir Gulch Watershed is warranted.