As part of an On Call Services contract, Matrix Design Group, Inc. provided preliminary and final engineering design services to the Town of Castle Rock for the stabilization of the Tract “F” drainage way tributary to East Plum Creek and the Omni Channel.

Due to increases in urban runoff over the last several decades, this ephemeral creek had become vertically and horizontally unstable, causing the erosion of thousands of cubic feet of sandy material during flood events and leaving the channels with nearly vertical cut banks. Erosion had reached the point where catastrophic landslides, property loss, mature tree destruction, and public safety hazards were imminent risks.

Matrix completed the initial assessment, alternatives analyses, and conducted public information process to involve neighbors and stakeholders in the selection of the preferred alternative. Hydrological modeling and hydraulic analyses were completed to properly design stabilization measures that would perform under a wide range of flows. Designs incorporated balanced grading plans, retaining walls, sloping grouted boulder drops, riprap revetment, and vegetation establishment. Matrix prepared the construction drawings, completed construction administration, and obtained floodplain development permits and erosion control permits for the projects.

The final solution involved the importation and re-grading of the majority of the lower reaches of the channel, the construction of several boulder drop structures, and armoring of the channel bottom and portions of the side slopes with grouted rip-rap. New connections to existing storm drain lines with energy dissipation and drop structures were also provided.