Dutchess Co, NY, Detailed Hydraulics

Resource lineage description

source

source description  Source Contribution: Spatial file that describes the downstream point where a riverine model starts.Source Type digitized

source citation

Title Reference location along the stream line

publication  Date   2006-01-01

cited responsible party - originator

organisation Name  Dewberry and Davis LLC

source

source description  Source Contribution: A spatial data set showing the centerlines of the stream network.Source Type digitized

source citation

Title Hydrologic Connectivity Network

publication  Date   2006-01-01

cited responsible party - originator

organisation Name  Dewberry and Davis LLC

source

source description  Source Contribution: A linear spatial file of cross sections.Source Type digitized

source citation

Title Cross Sections

publication  Date   2006-01-01

cited responsible party - originator

organisation Name  Dewberry and Davis LLC

source

source description  Source Contribution: A linear spatial file containing draft 100-year flood boundaries.Source Type digitized

source citation

Title Draft 100-year flood boundaries

publication  Date   2006-01-01

cited responsible party - originator

organisation Name  Dewberry and Davis LLC

AbsoluteExternalPositionalAccuracy

name Of Measure Horizontal Positional Accuracy Report

evaluation Method Description  Floodplain boundaries are derived from the hydraulic models developed for this Flood Insurance Study by automatically intersecting the 1-percent-annual-chance water surface elevations from the hydraulic models at cross section locations with the input ground elevation (i.e., the DCS Terrain data). The horizontal accuracy of the resulting floodplain boundaries reflects the horizontal accuracy of the source terrain data. As with any engineering analysis of this type, variation from the estimated flood heights and floodplain boundaries is possible. Details of FEMA requirements for the FISs and flood mapping process that produces these data are available in the Guidelines and Specifications for Flood Hazard Mapping Partners. Horizontal accuracy was tested by manual comparison of source terrain data and floodplain boundaries using hardcopy plots and a symbolized display on an interactive computer display.

AbsoluteExternalPositionalAccuracy

name Of Measure Vertical Positional Accuracy Report

evaluation Method Description  Analyses of the characteristics of flooding from the sources studied were carried out to provide estimates of the flood elevations for selected recurrence intervals. Flood elevations are developed at cross sections and interpolated between cross sections. The vertical accuracy of the computed flood elevations reflects the vertical accuracy of the source data. As with any engineering analysis of this type, variation from the estimated flood heights and floodplain boundaries is possible. Details of FEMA requirements for the FISs and flood mapping process that produces these data are available in the Guidelines and Specifications for Flood Hazard Mapping Partners. Vertical accuracy was tested by manual comparison of source terrain data and floodplain elevations using hardcopy plots and a symbolized display on an interactive computer display.

Completeness Commission

evaluation Method Description  Hydraulic analysis provides water surface elevations at different locations along the stream and for different flooding events. Hydraulic submittal includes key physical data used in the process, model parameters and model output. Data developed in surveying and hydrologic analysis are incorporated in hydraulic analysis. Results of hydraulic analysis are used to map Special Flood Hazard Area (SFHA) boundaries. Selection of model parameters (e.g. roughness coefficients, expansion and contraction coefficients, etc) is supported by additional information (e.g. landuse, aerial photo, etc). Model boundary conditions are carefully selected and justified. Modeled velocities are checked for potential erosion.

Completeness Omission

evaluation Method Description  Hydraulic analysis provides water surface elevations at different locations along the stream and for different flooding events. Hydraulic submittal includes key physical data used in the process, model parameters and model output. Data developed in surveying and hydrologic analysis are incorporated in hydraulic analysis. Results of hydraulic analysis are used to map Special Flood Hazard Area (SFHA) boundaries. Selection of model parameters (e.g. roughness coefficients, expansion and contraction coefficients, etc) is supported by additional information (e.g. landuse, aerial photo, etc). Model boundary conditions are carefully selected and justified. Modeled velocities are checked for potential erosion.

ConceptualConsistency

measure Description  Hydraulic analysis uses all valid existing flood elevation, survey, hydraulic analysis results and other pertinent information for the study area. FEMA approved models are used to compute water surface elevations for required flood events. Computed water surface elevations and topographic data are used to delineate flood hazard boundaries. Roughness coefficients are carefully selected to represent the conditions along stream beds and banks. Base Flood Elevations (BFEs) on the FIRMs and in floodway data tables agree with the flood profiles in the FIS.