The necessities to improve water recreation on the Mill Creek in Walla Walla

Abstract

In Walla Walla, Washington the Mill Creek flows through an outdated concrete spillway that needs renovation. The city council of Walla Walla saw this as an opportunity to further develop this channel. Their desires include conservation of the fish ladder, enabling to sail by boat and to prettify the spillway. A Sobek 1D model was built to give a proper insight of the current situation. To verify the model calibration was done by using USGS data and GIS maps of the Walla Walla council. Also various design alternatives were specified to see which form of recreation is most feasible. The results from the model in the current situation showed that the water depth was too low while its velocity was too high for the different vessels. To solve this issue, an upgrade for the concrete spillway was proposed. By roughening the riverbed and placing groynes into the creek, the water depth increased and the water velocity dropped, according to the improved model. However, the design is a rough sketch that forms the base for a more detailed study. It is recommended to continue improving the model to verify the results which are presented in this report to be sure the proposed upgraded design will contribute to the desires.