1. DATA COLLECTION. Obtain, review, and confirm data for Infoworks ICM (preferred platform) 2D model development. This includes existing infrastructure data, terrain data, rainfall data, and survey. All data collected will be aggregated into a GIS database for the area of study. a. Collect and Review Existing Infrastructure Data - Collect existing infrastructure data and as-built plans for the storm sewer from the City, Brazos County, and Texas Department of Transportation (TxDOT). Collect any previous models developed by the City for incorporation. Current 2D model is missing significant number of TXDOT storm sewer and culverts as plans were not available from TXDOT and survey not performed. So, some allowance for field surveying to pick up this information should be anticipated. The goal is to create an accurate 2D model that can be utilized to find drainage problems and to develop solutions to those problems. b. Collect and Review Terrain Data - Obtain the latest LiDAR from the City and review for major discrepancies due to recent developments or other inaccuracies in the base data. c. Collect Flood Claim Data - Collect historical flood claims data from the City or other available sources. d. Surveying and Site Visits - conduct site visits throughout the study area to identify and confirm watershed and infrastructure characteristics including supplemental surveying to obtain data. e. Draft Data Collection Technical Memorandum - Summarize data collection in a draft technical memorandum for the study area. The final data collection technical memorandum will be included in the final report. 2. HYDROLOGIC AND HYDRAULIC MODEL DEVELOPMENT. Develop model for the City including the storm sewer, roadside ditches, and channels within the watershed. a. Hydrologic Analysis - Conduct a hydrologic analysis of the study area. Delineate rainfall infiltration zones adhering to the City criteria for infiltration. Conduct rain on mesh hydrology within the city limits using Atlas 14 rainfall. b. Hydraulic Analysis - Conduct a hydraulic analysis of the study area. i. Configure the GIS information for importing into model and incorporating adjustments made during Data Collection task. ii. Input nodes needed for developing hydraulic model including elevations, storage volumes, areas, and ponding type. iii. Ensure continuity between node and link references. iv. Input links needed for developing hydraulic modeling including inverts, lengths, Manning’s n-values, sizes, and shapes. v. Import the refined terrain into model. vi. Develop break lines for the study area based on detail needed for the study. vii. Develop and import structures for the 2D surface. Simplify vertices as necessary for a clean mesh. viii. Assign Manning’s roughness values using land use polygons based on available data. ix. Mesh the 2D zone and review for unnecessarily small cells and inconsistencies. x. Refine 2D model components for model stability and reasonable run times. xi. Roadside Ditch Systems - Model roadside ditches within the 2D mesh. Use HECRAS terrain editing, or another GIS process to “burn” through driveway culverts in the LIDAR. Model culverts that cross roadways, and other significant culverts as 1D links using information from GIS or field verification. xii. Boundary Conditions - incorporate iterated flows with adjacent watersheds as necessary. Simulate model the 2-, 10-, 100-, 500-year Atlas 14 storm events for a preliminary analysis and verification of model stability. Debug model development and results to minimize errors and ensure stability. c. Model Validation - Perform a model validation of the hydrologic and hydraulic model using historical flood locations. d. Final Simulations - Simulate the final validated model for the 2-, 5-, 10-, 25-, 50-, 100-, and 500-year storm events. e. Draft Model Development Technical Memorandum - Draft and submit a technical memorandum summarizing the model development, validation effort, and results to the City for approval. 3. FLOOD RISK IDENTIFICATION. Utilize the hydrologic and hydraulic model to identify areas within Bryan with high flood risk. a. Flood Risk Area Identification - Utilize the results from the model to identify areas of high flood risk within the City. These areas can be areas of significant structural flooding, lowwater crossings, major roadway inundation, single access point neighborhoods, and other areas. b. Preliminary Project Recommendation for High Flood Risk Areas - Provide preliminary project recommendations for any identified flood risk areas. The project recommendations are considered high level and require additional detailed modeling outside of this effort to become finalized project recommendations. c. Draft Flood Risk Technical Memorandum - Summarize the results of the flood risk identification assessment in a technical memorandum to submit to the City for review.
