Sun Creek Hydromodification Planning
The Sun Creek development is a 1,250 acre proposed development within the City limits of Rancho Cordova.
Mackay & Somps is the civil engineering consultant responsible for the master plan for this proposed community. cbec is employed as sub-consultant to Mackay & Somps, and is currently undertaking hydromodification planning for the Sun Creek Stormwater Master Plan in the Laguna Creek watershed.
The initial stages of cbec’s work on this project included geomorphic reconnaissance of over 5 miles of Sun Creek, the central drainage of the proposed development. The purpose of this reconnaissance was to determine the existing susceptibility of the creek to the future impacts of hydromodification. cbec surveyed cross sections through this reach for modeling purposes, installed water level recorders (pressure transducers) to measure flood stages in the channel, and took sediment samples in the creek bed and banks which were analyzed to provide the erodibility potential (critical shear stress) of the soils in the region . cbec also installed turbidity sampling probes to provide sediment data for modeling purposes. cbec continues to monitor the creek for stage, velocity and sediment transport.
cbec modeling staff undertook long-term continuous hydrologic modeling using HEC-HMS to develop flow duration modeling for existing and proposed conditions. The data provided from the hydrologic modeling was used to supply input boundary conditions for 1Dhydrodynamic modeling using MIKE 11. The results of the hydrodynamic modeling were used to assess the erosion potential under proposed developed conditions, where the erosion potential is the ratio of the work done in the channel after development to the work done in the channel prior to development– an erosion potential greater than one generally will result in channel erosion and degradation, while an erosion potential less than one generally will result in aggradation and sediment build up. In order to assess the requirements for mitigation of hydromodification, the flow duration curves were matched for pre- and post-hydrologic conditions and the erosion potential was matched to around 1.0.
Hydromodification mitigation was theoretically undertaken using LID and flow duration control approaches to match pre- and post-project hydrology. cbec assisted with concept designs for multi-purpose flow duration control-water quality-storm detention basins. Of particular concern, the designs are addressing the infiltration and evapotranspiration of summer irrigation runoff flows.