Drainage Investigation for Storm Water Runoff and Tidal Flooding, San Pablo Bay, CA
The drainage investigation identified potential causes of flooding at a development bordering the San Pablo Bay waterfront. The concurrent high tide condition with heavy rainfall was found to cause backflow from the storm drainage system into the development. Ground subsidence at the site has also contributed to increased flooding conditions. Dr. Lewandowski performed SWMM modeling to simulate the unsteady flow caused by peak rainfall runoff and varying tidal levels. The modeling confirmed upwelling of offsite flows into the development at peak tide levels at spring tide. He then developed an innovative approach using a combination of landscaping walls for offsite flooding protection and a single pump station for internal system runoff. This approach, combined with modifications to the existing City storm drain system, provided the lowest cost flood flow management solution for protecting the development from offsite overland flows. Dr. Lewandowski also assisted with preliminary environmental review of permitting requirements and costs associated with Army Corps of Engineers permits and for BCDC permitting. Permitting requirements were incorporated into the alternative analysis.
Low Water Pressure Investigation, Sacramento, CA
A 260 unit development in Sacramento, CA had numerous reports of low water pressure throughout the development. Dr. Lewandowski developed and implemented a pressure monitoring strategy to identify possible causes of the low pressure conditions. Average daily demands and peak daily water demands were determined for the development. Measurement, review and analysis of metering station equipment pressure loss were also performed. The water system network was analyzed to determine whether pipe sizes were adequate to convey peak demands without significant pressure reductions.
Storm Drain Pipe Failure Investigation, Marin County, CA
A school experienced significant flooding after a modernization project was completed. The project included revisions in the storm drain piping network and changes in surface drainage routes. Dr. Lewandowski reviewed hydraulic conditions prior to the project construction for comparison with hydraulic conditions during the flooding event. The flooding contribution of the failure of a pipe liner installed in the storm drain that crossed the campus was also reviewed during the analysis.
Water Supply, Treatment and Storage Investigation, Central Valley Foothills, CA
A residential development of estate homes in the foothills of the Central Valley experienced water system operation issues. These issues included water shortages and low operating pressures during peak demand periods, as well as inadequate fire flow rates from hydrants at the site. In addition, water quality issues existed related to iron and manganese concentrations that exceed secondary maximum contaminant levels (MCLs) and State of California Department of Health Standards. Dr. Lewandowski performed an initial investigation of the water supply, treatment, storage and distribution issues at the development. A water balance summary of the water supply, demands and storage requirements for the development was completed. The available water supply was developed from long term well capacity previously identified. Demands were based on County and State standards, and from water production records from recent years. Dr. Lewandowski developed water storage requirements based on County and State standards.
Subsurface Drainage Investigation, Marin County Homeowners Association, Marin County, CA
Excessive moisture was observed in building crawlspaces in a development in Marin County. The moisture was attributed to high groundwater conditions. Dr. Lewandowski performed an investigation to assess the subsurface drainage conditions at the development and reviewed previous reports regarding subsurface drainage issues. High groundwater conditions appeared to be impacting condominiums and other structures that were keyed into the hillside. The subsurface drainage facilities (subsurface drains and sump pumps) originally installed for the lower units at the lowest elevations appeared to be inadequate to maintain an appropriate groundwater level to prevent ground surface moisture conditions below the units. Also, the groundwater sump pumps installed under the units did not meet current plumbing code requirements. Retrofit with new subsurface drainage facilities was proposed, including new tile drains below the unit and measures to intercept and convey groundwater to the tile drains. Due to the continuous flowing nature of these drains, connection to the existing storm drain was recommended.