Hydrologic Analysis a. The Engineer shall create a hydrologic analysis using HEC-Hydrologic Modeling System (HEC- HMS) if watershed or area of interest is larger than 200 acres. The Engineer shall review and comment on the hydrologic analyses of said analysis and portions of the Project; and
b. The Engineer shall review and comment on the comparison of peak flow rates for the Project with any available data from the National Flood Insurance Program (NFIP) or other studies to determine consistency of results.
Hydrologic Analysis. Developer shall design the drainage system to accommodate the ultimate development of the drainage areas. Flood damage potential for the completed Project shall not exceed pre-Project conditions.
Hydrologic Analysis. This effort includes updating prior planning studies and developing new hydrologic analysis to reflect current conditions in the county. Detailed hydrology will be conducted within 1,380 square miles in Xxxxxxxxxx County supplemented with leverage hydrology totaling 1,110 square miles beyond the county boundary. Xxxxx County will be conducting hydrology on 320 square miles to complete hydrologic analysis on the remainder of the HUC-10 watersheds. Xxxxxxxxxx County hydrologic analysis shall include evaluation of the existing condition 2-, 10-, 25-, 50-, 100-, and 500-year frequency events using the latest version of HEC-HMS. Specific tasks include:
a) Update of Prior Studies – Update prior hydrologic analysis using Atlas 14 rainfall data, current LiDAR, and land use conditions.
i) Revise drainage area boundaries based on new terrain information and sub-divide basins where appropriate for analysis of study streams.
ii) Convert the prior hydrologic models to the latest version of HEC-HMS.
iii) Update hydrologic loss parameters, hydrograph transform, and timing parameters to achieve consistent results with the prior studies.
iv) Update storage tables, routing curves, and compute revised discharges. The Modified-Xxxx storage-discharge relationships will be based off the updated hydraulic models in Task 4.
b) Conduct New Analysis – Consistent with the analysis and updates noted above, conduct new hydrologic analysis using Atlas 14 rainfall data, current LiDAR, and land use conditions.
c) Model Calibration / Validation – Verify modeling results using historical events, gage statistics, prior studies, and/or adjacent watershed studies. Two historical events will be evaluated for comparison of runoff along detailed study reaches with gage information.
Hydrologic Analysis. This effort includes updating prior planning studies and developing new hydrologic analysis to reflect current conditions in the County. Detailed hydrology will be conducted within 1,380 square miles in Williamson County supplemented with leverage hydrology totaling 1,110 square miles beyond the County boundary. Milam County will be conducting hydrology on 320 square miles to complete hydrologic analysison the remainder of the HUC-10 watersheds. Williamson County hydrologic analysis shall include evaluationof the existing condition 2-, 10-, 25-, 50-, 100-, and 500- year frequency events using the latest version of HEC-HMS. Specific tasks include:
a) Update of Prior Studies – Update prior hydrologic analysis using Atlas 14 rainfall data, current LiDAR, and land use conditions.
i) Revise drainage area boundaries based on new terrain information and sub-divide basins whereappropriate for analysis of study streams.
ii) Convert the prior hydrologic models to the latest version of HEC-HMS.
iii) Update hydrologic loss parameters, hydrograph transform, and timing parameters to achieve consistent results with the prior studies.
iv) Update storage tables, routing curves, and compute revised discharges. The Modified- Xxxx storage-discharge relationships will be based off the updated hydraulic models in Task 4.
b) Conduct New Analysis – Consistent with the analysis and updates noted above, conduct new hydrologic analysis using Atlas 14 rainfall data, current LiDAR, and land use conditions.
Hydrologic Analysis. For example, a calibrated, continuous-simulation model must be used to estimate runoff in western Washington for flow control best management practices (BMPs). In the case of infiltration facilities, the output from this runoff analysis is combined with estimates of infiltration rates to select the size and geometry of the infiltration facilities. This is described on page 141 of Volume III (included in Appendix A of this report): "The analysis must demonstrate that the BMP will completely infiltrate the design storm within 24 hours (or 48 hours for the 100-year event). If this is not the case, the surface area of the BMP will have to be increased." The recommended approach for sizing infiltration facilities is summarized in Section 2.3.8, pages 140-142 in Volume III of the Washington Department of Ecology draft manual (WDOE, 1999a). The approach is based on using Xxxxx'x law for saturated ground flow, assuming constant hydraulic conductivity and constant gradient. Although the manual points out that "Xxxxx'x Law is difficult to apply to unsaturated flow conditions," it does not suggest other approaches or analytical tools for estimating infiltration rates. In most cases, the uncertainties in estimates of infiltration rates will be significant. It would not be uncommon for the actual, long-term infiltration rate to differ from the estimated infiltration rate by factors of 2 to 10. These differences are primarily due to uncertainties in hydraulic conductivity and hydraulic gradients and because of errors in using the saturated flow equations presented on page 140 to describe infiltration. In the case of infiltration facilities, it not clear that the resources and efforts that are required to estimate surface runoff are justified, given uncertainties inherent in infiltration rate estimates. Or, from another viewpoint, it is not clear that the simplified approach recommended for sizing infiltration systems is justified given the requirements for estimating runoff. It may be appropriate in at least some cases to shift the emphasis to developing better estimates of infiltration rates. This could be accomplished with more sophisticated analytical tools for describing the infiltration process (including computer models) and with more reliable estimates of site characteristics. For example, analytical approaches for estimating infiltration rates from impoundments are presented by XxXxxxxxx and Xxxxxx (1979). The Green-Ampt approximation to Xxxxxxx's equation may a...
Hydrologic Analysis. ▪ Develop the design flows using StreamStats. ▪ Verify StreamStats basin delineation utilizing available Lidar. ▪ Check StreamStats flows against any nearby gage data and a ratio of the drainage basins. ▪ Calculation of peak discharges for the 2-year through 500-year floods as well as any flows necessary for meeting fish passage requirements.
Hydrologic Analysis. 1. Prepare Drainage Area Maps and determine sub-drainage areas.
2. FEMA effective modeling and discharges, or other previous study discharges, will be used to establish design discharges for Long Branch and Stream 2E3/2E4 confluence.
Hydrologic Analysis. The Engineer shall use data from as-built plans and field surveys to locate drainage outfall(s) and to determine existing storm sewer and culvert sizes, design flows, and water surface elevations for use in the design of roadway geometry. The Engineer shall conduct a Preliminary Drainage Study to determine and evaluate the adequacy of the ROW needed to accommodate the proposed roadway and drainage system. The drainage study shall identify the impacts to abutting properties and the 100-year floodplain due to proposed highway improvements, identify the water surface elevations for the design frequency and 100 year storm events, identify and locate outfalls, drainage outfall descriptions, provide overall drainage area map, sub-drainage area map, storm water detention facilities, and provide a drainage study report identifying the results of the study. The Engineer shall not evaluate the adequacy of the existing drainage structures, unless directed by the State.
Hydrologic Analysis. Sufficient base line data shall be established prior to conducting any surface disturbing activity which shall be determined necessary by the AO. In order to accomplish this, the lessee shall submit for review and approval by the AO a plan to analyze ground and surface water interactions as part of any operations or exploration on the leases. The plan shall be submitted prior to or concurrent with a Mining or Exploration plan under 43 CFR 3592.1. The plan shall include, but not be limited to the following items, and shall describe how the lessee proposes to; (1) develop sufficient baseline groundwater information to document existing hydrogeology associated with Xxxxxx Lake basin fill and underlying carbonates, encompassing a reasonable area of potential resources, springs, and the alluvial and bedrock aquifers. This shall include items such as the location, size, and depth of any hole that will encounter water and/or brine as well as any information that will be collected on each hole.
Hydrologic Analysis. Hydraulic Analysis with Flood Reduction & Fish Passage Assessments (Water surface profile modeling run with storm flows, median monthly flows, and 5th and 95th percentiles of the flow range associated with the fish passage migration period, and assessment of flood impacts/attenuation)
