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HCFCD Review Process - Harris County Flood Control District
HCFCD Review Process Impact Analysis Local Review LOMR Delegation Local Review This presentation will include: Why is this step important? Process Review Checklist Common Comments 2 Local Review Why is this step important? Per MAS 14, Local Review is required so that HCFCD is the custodian of the models (M3) To provide technical support to Floodplain Administrators (FPA’s) To maintain current models and GIS shapefiles consistent with applicable standards Make sure all information is included for LOMR Delegation review Protect the community Investment 3 HCFCD Review Process Impact Analysis Local Review Detailed or Cursory Review LOMR Delegation Data Required for Cursory Review For jurisdictions other than Harris County Unincorporated: Design or As-Built Plans M3 Models and effective Topographic Work Map GIS Data Used Modeling and GIS Data standards followed Certified Survey Annotated FIRM Annotated FIS Profile Annotated FIS Tables Data Required for Detailed Review Impact Analysis Approval Letter Request for LOMR/CLOMR with a no adverse impact statement HEC-HMS models Annotated FIRM Design or As-Built Plans Certified Survey Annotated FIS Profile HEC-RAS models Annotated FIS Tables Topographic Workmap GIS Data Model Version Requirements Version needs to match effective model Effective models can be download from http://www.hcfcd.org/m3/ The effective model version is indicated in the ReadMe document included in the download Modeling Naming and Definitions Duplicate Effective Represents a copy of the effective model Reproduces the same results as the effective model Corrected Effective Per FEMA guidelines, is the model that corrects any errors that occur in the Effective Model Adds any additional cross sections to the Effective Model Must be non project related Adds additional, more detailed topographic information Not required unless technical errors are being corrected Modeling Naming and Definitions Pre-Project Represents an existing condition prior to construction of the proposed project Reflects changed conditions in the watershed or stream since the date of the effective model Required to support conclusions about the actual impacts of the projects Modeling Naming and Definitions Post-Project/Proposed Represents a view of the watershed, stream, or detention facility after the project is complete Pre-Project Model or Corrected Effective Model modified to produce the Post-Project/Proposed Model Results are compared to the Pre-Project or Corrected Effective Model results to determine if there are any impacts of the project HEC-RAS: Cross sections cannot be added/ removed in the Post-Project/Proposed Model Modeling Naming and Definitions Required HEC-RAS Steady Flow Profile Names 10PCT_10yr 2PCT_50yr 1PCT_100yr 0.2PCT_500yr 1PCTFloodway_100yrFW HEC-HMS Model Checks It is recommended to not revise effective flow if the change is less than 10% Only include necessary plans Rainfall Follow rainfall procedures outlined in Section II.2 of the H&H Guidance Manual Subbasin Boundary Modifications Any proposed changes in the boundaries or further subdivision require prior approval by HCFCD Only subbasin boundary changes that will results in a revision of the FEMA effective model require prior approval Loss Rates Green and Ampt Infiltration Methodology described in Section II.2 and II.3 of the H&H Guidance Manual HEC-HMS Model Checks Unit Hydrograph Clark’s Unit Hydrograph Methodology described in Section II.3 of the H&H Guidance Manual Hydrologic Routing Modified Puls routing for all routing reaches for which an effective model is available Methodology described in Section II.4 of the H&H Guidance Manual Detention Facilities Refer to Section 6 of HCFCD’s PCPM and Section II.7 of the H&H Guidance Manual Off-Line Detention Baseflow – Do not use HEC-RAS Model Checks Only necessary plans included Flows and flow change locations match effective model Cross Sections Must not be interpolated Surveyed within channel banks, LiDAR or survey in overbanks Aligned normal to direction of flow Centerline stationed at 5000 GIS Cut Line Ratio = 1.0 Geometry matches survey/plans For fill, elevations of the topo should be adjusted (blocked obstructions should not be used) Storage within detention ponds should be represented with blocked obstructions to avoid double-counting storage Correct contraction/expansion coefficients used Manning’s n value consistent with surrounding cross sections (quick check) Ineffective flow areas used correctly and at right location HEC-RAS Model Checks Boundary Condition Match effective condition unless prior approval from HCFCD is obtained Bridges Geometry matches provided plans Method Deck low and high chord elevations (NAVD 88, 2001 Adjustment) Pier size and location Bridge span lengths Most bridges in Harris County are modeled with the Energy Equation for low flow and high flow conditions Appropriately placed cross sections Ineffective flow areas at correct locations HEC-RAS Model Checks Culverts Geometry matches provided plans Size, flowline, number of culverts (NAVD 88, 2001 adjustment) Roughness coefficient matches material Appropriately placed cross sections Ineffective flow areas at correct locations Are Proposed/Post-Project water surface elevations are higher than Effective or Corrected Effective/Pre-Project conditions model? Floodway If no floodway revisions, encroachments at added cross sections are stationed at the location of the existing floodway location Surcharges cannot be greater than 1.0 foot or less than 0.0 feet. Topographic Workmap Certified by a registered professional engineer Scale and North Arrow Project Boundary Boundary delineations of the effective and revised conditions base (1%-annualchance) floodplain, 0.2%-annual-chance-floodplain, and regulatory floodway Logical tie-ins between the revised and effective flood hazard boundary delineations Topographic contour information used for the boundary delineations Locations and alignments of all cross sections used in the hydraulic model Stream centerline used in the hydraulic model Reference datum, NAVD 88, 2001 Adjustment Annotated FIRM Must be based on effective panel Match scale of the effective FIRM Shows the revised boundary of the base (1%-annual- chance) floodplain, 0.2%-annual-chance-floodplain, and regulatory floodway All affected FIRM panels included Annotated FIS Profiles Matches format of the effective profile Paper and digital (.mdb and .dxf) files provided Annotated FIS profile should be created using RASPLOT Available for download at https://www.fema.gov/national- flood-insurance-program-flood-hazard-mapping/rasplotversion-30-beta Revision box includes all revised water surface elevations Should match the S_LOMR boundary in the topographic workmap Annotated FIS Tables Floodway Data Table Matches format of the effective table Paper and digital (.xls) files are provided Revision box consistent with topographic workmap and FIS profile Summary of Discharges Matches format of the effective table Paper and digital (.doc or vector .pdf) files are provided Revision box consistent with topographic workmap and FIS profile Local Review: Common Comments Please provide all the required GIS shapefiles layers according to FEMA standards, which demonstrate the added cross sections, the revised floodplain, the revised base flood elevation, and any other information that is applicable for this submittal. Our review reveals an increase in water surface elevation between the preproject and the post-project. Please revise the model to show no impacts. To ensure that you are aware of changes to the effective models, please submit an online request for FEMA effective models through the M3 System www.hcfcd.org/M3. Upon completion of your M3 request, you will receive an M3 Tracking Number. Future submissions of this report and FEMA submittals for this project will be required to reference the M3 Tracking Number. 21 BREAK (15 Minutes) 22
