Hydrologic and Hydraulic Analysis. Conduct required H&H analyses to assess existing and proposed conditions. Analyses should be performed for the 2-year (50% annual exceedance probability (AEP)), 10-year (10% AEP), 100-year (1% AEP), and 500-year (0.2% AEP) storm events. The existing condition modeling will be based on the Xxxx-Xxxxxx Big Creek model completed in 2020 for Fort Bend County. This model includes updated rainfall per recent revisions to Atlas
Hydrologic and Hydraulic Analysis. The existing and proposed condition XPSWMM models within the City’s Storm Drain Master Plan will be reviewed and adjusted to facilitate the final design of the preferred alternative storm drain alignment. It is anticipated that the proposed condition models will include identifying a new storm drain alignment that will route flows to the North Truckee Drain. As part of this realignment, an inlet analysis will be performed. If the proposed storm drain cannot be constructed or design criteria cannot be met to meet City standards due to utility location or other constraints, coordination with the City will be conducted to determine the optimal design condition. It is assumed that: • Drop inlet locations will not change in the proposed condition and that an analysis will not be required as no known problems exist in this area. • Drainage basins will not be modified from the master plan basins. • Tailwater conditions on the North Truckee Drain will be evaluated for the design and agreed upon with the City. • While the City’s Storm Drain Master Plan was modeled with XPSWMM, the City may want the final design completed with InfoSWMM. The post-project hydraulic analysis results will be summarized in Task 5 to identify the additional storm drain capacity that will be achieved with the construction of this project. In addition, the final report will show that there will be no adverse impacts associated with the preferred design.
Hydrologic and Hydraulic Analysis. This project is located in the Floodway of the West Fork Trinity River and within the Trinity Corridor Development Certificate (CDC) floodplain boundary. The preliminary alignment of the trail crosses the Unnamed Tributary to the West Fork Trinity River as well as the Unnamed Tributary to Walnut Creek 2. The trail is also located within the FEMA SFHA floodway of the West Fork Trinity River. Due to the location of the project, permitting applications are required through the City, TXDOT and the CDC. The project is not anticipated to cause changes to the FEMA floodplain or floodway, so a CLOMR/LOMR is not included in the scope of this project. The items below describe our understanding regarding drainage for the scope of this project.
Hydrologic and Hydraulic Analysis a. Rapid 2D Assessment
Hydrologic and Hydraulic Analysis. 4.1. Perform a hydrologic analysis of the Sheridan Drain and unnamed tributary (UNT) to the Upper Trier regulated drain watersheds. The analysis will separate the watershed into a maximum of six subareas. Existing and proposed condition flow rates will be determined for the 10%, 2%, and 1% exceedance probability storm events. The proposed watersheds will include as much of the Sunnymede Subdivision that is able to be discharged to the selected outfalls. The calculation methodology will be determined based on the watershed characteristics and the Allen County Stormwater Technical Standards Manual.
Hydrologic and Hydraulic Analysis. The horizontal screen design process must include an analysis to verify that sufficient hydrologic and hydraulic conditions exist in the stream so as not to exacerbate a passage impediment in the stream channel (see Section 4.1), or in the off- stream conveyance, including the screen and bypass. This analysis must conclude that all criteria listed below can be achieved for the entire juvenile outmigration season, as defined by section 3. If the criteria listed below cannot be maintained per this design analysis, a horizontal screen design must not be used at the site. If this analysis concludes that removal of the bypass flow required for a horizontal screen from the stream channel results in inadequate passage conditions or unacceptable loss of riparian habitat, other screen design styles must be considered for the site and installed at the site if adverse effects are appreciably reduced.
Hydrologic and Hydraulic Analysis. Since Task 3 includes development and evaluation of alternatives, to some extent, it must occur concurrently with Task 5, Preliminary Design. After the initial review of flooding issues and potential treatment facilities with the City, we propose that the design team and the City conduct a series of meetings to develop alternatives and specific information needs to confirm that each alternative is indeed technically feasible. Many objectives, such as stabilizing road shoulders and replacement of undersized storm drains, will be straightforward and will not require such an approach. However, development of alternative treatments related to the location and function of treatment basins, possible stormwater diversions, and floodplain restoration measures will be most effectively done using a team approach to identify information needs and to also provide an initial assessment of cost feasibility where easements or land acquisitions may be required. In essence, we propose an alternative development and feasibility screening process as an additional Task 3 subtask. We believe this will reduce costs associated with surveying, geotechnical, and NEPA/CEQA analysis as the design progresses. The stormwater treatment facilities designed as part of the alternatives analysis shall at a minimum capture, treat, and infiltrate storm water runoff from the 550-acre contributing drainage area (watershed) and infiltrate 72 acre-feet of stormwater. We propose to undertake Task 3.2 as shown in the RFP prior to initiation of Task 3.1 since it provides the information prerequisite to the design process.
Hydrologic and Hydraulic Analysis. Hydrologic and hydraulic analysis will continue building off of the efforts completed during Phase 1 in order to investigate new alternatives introduced during the later stages of 30% design and support design development as it moves through 60% and 90% detail levels.
Hydrologic and Hydraulic Analysis. Data Collection for Hydrology/Hydraulic Tasks: Data collection and model inventory tasks will generally include gathering, organizing, and reviewing of all data provided, both hard copy and digital format. Data shall be provided by the County, as well as from other sources such as Hidalgo County Drainage District No. 1, Texas Department of Transportation, Franchise Utility Companies, FEMA, the U.S. Army Corps of Engineers (USACE), and other consultants, if necessary. Data review tasks will generally include comprehensive analysis of all models, studies, reports, record drawings, and GIS information to determine the accuracy and validity of each. Halff will also review the current drainage criteria and work with the County to recommend any potential changes or clarifications that may be needed. Hydrology and Hydraulic Modeling Halff will study the contributing watershed and utilize existing H&H models developed for the County as the basis for building a combined 1D hydrologic and hydraulic model using InfoWorks ICM. Halff will modify basins as needed for proposed facilities, develop improvements that will help facilitate the storage and conveyance of storm water runoff. Halff will perform other updates that may include modification of development levels, updated terrain information, etc. Proposed hydrologic and hydraulic facilities will be designed per the current County development guidelines and criteria. The results of the H&H modeling will be used to develop the construction documents. Modifications to the drainage design arising from the detailed design process will be documented in the overall model to reflect the completed design conditions and delivered to the County with the construction documents submittal.
