Additional services provided by PHI and not described on separate pages include the following:
- Local agency review of new development and redevelopment
- Drainage master plan analysis
- Detention studies
- Local drainage design standards and drainage manuals
- Precipitation analysis
- Construction period flood and erosion risk analysis
- Reservoir operations models
- Riverine temperature models
- Stream flow measurement
Example Projects
Greater Houston Wastewater Program.
The Greater Houston Wastewater Program (GHWP) was formed by the City of Houston to meet a legislative requirement that major metropolitan areas reduce Combined Sewer Overflows (CSOs). Sewer overflows in the GHWP service area are primarily due to infiltration and inflow (I&I) to the sewer system during and shortly after storm events. Most large metropolitan areas chose to address the new requirements of reducing CSOs by designing facilities to accommodate flows resulting from two consecutive 5-year or 10-year design storm events. This approach was known to be very conservative and fails to recognize opportunities to reduce CSOs by transferring wastewater from overwhelmed collection systems within the service area to collection systems operating under capacity. The GHWP chose to investigate the possibility of using continuous simulation modeling of the collection systems for identification of potential options to minimize CSOs.
Prior to the development of more recent continuous simulation dynamic storm drainage models, PHI was retained to modify the USEPA “Extran” dynamic transport module of the EPA Storm Water Management Model (SWMM) for operation as a continuous simulation model between periods of low runoff. PHI was also retained to assist with development of a preprocessor program to convert precipitation into a hydrograph representing I&I, a precursor to InfoSWMM, and to develop a post processor program for summarizing the reams of model output. Using the continuous simulation model with pre and post processor programs it was possible to identify and evaluate how the present sewer collection system would have performed when exposed to the prior 50-years of storm events. The model was further used to evaluate approaches to minimize CSOs. The model was proven and was relied upon by GHWP for design of measures to meet the legislative requirements. Use of the model contributed to considerable savings in facility costs over the design storm methodology and allowed the City of Houston to become the first major metropolitan area to meet the legislative requirements.
Yolo County Development Review
When faced with a number of proposed residential developments tributary to and encroaching within wide, shallow floodplains and with a number of habitat conservation bank projects affecting topography and vegetation within established flood bypass channels, staff at Yolo County required assistance evaluating studies addressing potential project flood risk impacts. Under an existing on-call contract, PHI has been retained to assist Yolo County by conducting independent reviews of drainage analyses and reports for sufficiency to meet appropriate requirements defined by the Yolo County Improvement Standards, the Yolo County Zoning Ordinance, the State of California Central Valley Flood Protection Board (CVFPB), FEMA, common law, and the local professional standard of care. Developments are reviewed to make sure there are no unacceptable or unmitigated increases in runoff, to make sure that floodplain encroachments do not increase the risk of damage to structures and properties during the Base Flood (most probable 100-year flood), and to minimize potential project related risks to channel instability. The reviews are paid for by the applicants.