Overview
The City of Raleigh Storm Drainage Assistance Program is funded for improvements on private property within the City limits. Timmons Group staff has helped the City with engineering evaluations and designs of over 90 projects to address infrastructure inadequacies and severe erosion. Designs focused on the relief of structural flooding through the improvement of drainage system capacity, evaluation of watershed detention opportunities, and the stabilization of natural stream corridors. Watershed analysis was completed using hydrologic models such as HEC-HMS or PCSWMM to predict peak discharges at points of interest and/or to evaluate potential opportunities to improve upstream storage within the system. To evaluate the system hydraulics and determine flood inundation limits, HEC-RAS, HY-8 and PCSWMM models were used for analysis and design.
Infrastructure improvement designs included recommendations for full pipe replacement to improve system capacity as well as in-situ repairs where applicable such as pipe lining, reconstruction of CMP inverts, and the use of expandable materials to seal joints where system degradation was the primary concern. Stream stabilization/restoration project design were completed to repair severely eroded banks, oftentimes endangering nearby existing infrastructure. Solutions were designed with natural channel techniques as well as reinforced structures as applicable. Base topographic surveys as well as a morphological assessments of the stream were completed to quantify existing stream dimension, profile, and bankfull conditions. Processing of this data included hydrologic and hydraulic analysis of the stream. Design goals included long term stability and improved stream function through reconnection to the floodplain, provision of bankfull benches, toe stabilization through the use of rock toe or other structural measures, use of natural materials such as log vanes, rock vanes, soil lifts, brush matts, replanting with native woody species and constructed riffles. The projects were developed for public bid including construction plans, project manuals, engineering opinions of probable cost and easement exhibits. Permits were obtained through the State of NC Land Quality, City of Raleigh, USA Corps of Engineers for 404, and NCDWR for 401 and buffer authorization permits. Assistance was provided to the City for project bidding, contract award, and construction administration assistance for design document compliance.
