Flood and Storm Water Drainage Analysis

Ygnacio Canal Storm Water Flood Study, Walnut Creek, CA Client: CCWD
The Ygnacio Canal is a loop canal in the Contra Costa Canal system that is located in the City of Walnut Creek, CA. The majority of the five mile canal length is a trapezoidal, concrete or asphalt lined channel, with depths ranging from 1.3 to 2.5 feet, and top widths from 5 to 7 feet. Portions of the Ygnacio Canal in Walnut Creek have been impacted by off-site drainage into the canal. Off-site drainage includes runoff from areas outside the canal right-of-way that have been directed into the canal for disposal. Dr. Lewandowski performed field investigations and identified off-site drainage areas that included direct discharge of runoff from major roadways, and sheetflow from an adjacent golf course. Other areas had potential overflow into the canal right-of-way during high rainfall due to lack of conveyance or storage capacity in offsite structures.

Pajaro River Watershed Study, Pajaro River Watershed Flood Prevention Authority, CA
The Pajaro River flooded large areas of Monterey, San Benito, Santa Cruz and Santa Clara Counties during 1995 and 1998, causing extensive and costly damage. The Phase 2 study included analysis of a number of different floodplain and channel improvements, with various levels of flood reduction. The goal was to allow comparison of the costs, impacts and benefits of each improvement, and to group improvements into alternatives that could provide flood protection from 100-year events. Dr. Lewandowski assessed improvements and reviewed the groups of alternatives for reduction of existing and future 100-year flooding areas. A large floodplain area known as Soap Lake was identified as crucial to preventing increases in flood flows. In Phase 3, the Soap Lake floodplain area was modeled in HEC-GeoRAS to verify the floodplain limits that occur in storm events from 2-year to 100-year return periods. Dr. Lewandowski directed the modeling efforts and performed technical review of the modeling results. In Phase 4, he performed technical reviews of the installation of real time data transmission equipment at two proposed stream gage sites in the Upper Pajaro River watershed. He also reviewed the rating curve of the San Benito River at the Highway 156 stream flow gage.

Community Storm Water Drainage Studies, Cities of Cayucos and Nipomo in San Luis Obispo County, CA
Dr. Lewandowski provided review and analysis of existing flooding problems in the Cities of Cayucos and Nipomo, CA. Both communities had no formal drainage master plans, resulting in a number of minor flooding problems within the urban boundaries. In Cayucos, he identified locations where new installation of storm drain pipelines would allow conveyance of excess runoff to the outfall locations near the beach, instead of creating localized flooding of surface runoff. The Olde Town area of Nipomo had a number of flooding areas, caused by landowner encroachment along the creek and constricted crossings at roadway culverts. The roadway crossing culverts were assessed to determine whether County design standards for return period capacity were met. The Mesa area of Nipomo has an undulating surface, preventing development of a regional storm water system. Improvements were identified to reduce flood hazards caused by standing water in the roadways and to reduce the flood impacts to structures and residences.

Stream Management Master Plan, Zone 7 Water Agency, Alameda County, CA
Dr. Lewandowski developed technical memorandums and provided technical assistance in the analysis of flood control problems and needs for the stream management master plan. He reviewed a number of previous studies to identify needs and problem areas which needed further study. He also performed a hydraulic analysis of flooding along Arroyo de la Laguna and Arroyo Mocho using HEC-RAS.

San Juan Basin Surface Drainage Feasibility Planning, San Benito County Water District, CA
Dr. Lewandowski performed a review and analysis of previous hydraulic and flooding studies completed for the San Juan Basin to identify potential for developing a regional drainage system. Drainage options available with the cross-basin Highway 156 reconstruction were identified. The plan identified potential revisions to the Caltrans Highway 156 improvements that could improve drainage of both highway and local runoff. The plan also included potential projects that could be completed in the basin, with or without Highway 156 improvements, to reduce flooding in other areas. Following this preliminary assessment, the results were more widely distributed for comment and discussion. Further discussions with local agencies were performed to develop a more comprehensive understanding of drainage issues within the basin, and the potential need for funding of drainage improvements. From this work with local agencies, an action plan regarding storm water management in the San Juan Basin was developed. During the second phase, detailed field investigations were performed to identify the watershed boundary and potential sites for storm water detention basins.

Upper Penitencia Creek Floodplain Study, Santa Clara Valley Water District, CA
Dr. Lewandowski performed hydraulic analyses of a number of alternative bridge crossings and channel configurations for the King Road bridge crossing on Upper Penitencia Creek. The proposed bridge size was increased or paralleled with a box culvert to pass the 100-year flow. Downstream flow conditions included a potential widened overbank riparian area to convey the 100-year flow without flooding.

Calera Creek Floodplain Study, Santa Clara Valley Water District, CA
For Calera Creek, Dr. Lewandowski reviewed the expected water surface elevations under a number of different flow conditions to determine the channel capacity in each reach of the creek. The capacity was compared with the 100-year flow rate to determine where flooding would occur. Capacity limitations were observed near culvert crossings and at an energy dissipation drop structure.Green Valley Creek and Jameson Canyon Creek Hydrologic Studies– Cordelia, CA:Dr. Lewandowski led the hydrologic and hydraulic analysis of both creeks to determine peak flow rates expected near the Cordelia Junction along Interstate 80. He also trained staff on HEC-HMS program operation. Creek flows were calculated from a HEC-HMS model for each watershed to determine peak flow hydrographs. Rainfall patterns were based on the assumed maximum intensity rainfall rate at the middle of the storm, with stepped intensities on each side of the peak, which was different than previous hyetograph assumptions. Peak flow rates expected at the freeway crossings were compared with previous design values and actual capacity of existing culvert crossing structures.

Suisun Creek Floodplain Study near Interstate 80 – Fairfield, CA
As project manager, Dr. Lewandowski led the hydraulic analysis of the flooding that caused overtopping of Interstate 80, and developed options to prevent its reoccurrence. Peak flooding in this area is a result of local runoff and overbank flow from Suisun Creek. Creek overflows were combined with runoff developed from a HEC-HMS model for watershed to determine peak flow hydrographs. A HEC-RAS model was developed for flow overtopping the freeway, and results were integrated into the HEC-HMS model to determine upstream flooding and flood flow attenuation in the area. Modeled alternatives including a potential upstream detention area created by a proposed roadway crossing, and a grade elevation increase of I-80 to prevent overtopping.

San Pablo and Wildcat Creeks Floodplain Assessment, San Pablo, CA
FEMA had proposed revisions to the City of San Pablo’s Flood Insurance Rate Map (FIRM) that included significantly greater flooding areas compared with previous mapping. The revised boundaries included a total of 340 acres in the floodplain, with an additional 1,200 homes included in the floodplain area. As project manager, Dr. Lewandowski reviewed the Preliminary FIRM boundaries and results of the HEC-2 and HEC-RAS models for both San Pablo Creek and Wildcat Creek prepared by FEMA. He also revised the models to include reductions in Manning’s n values, recent channel improvements and bridge modifications, and an updated topographic map with 2-foot contours. After the adjustments, the floodplain developed from the revised model included only 140 acres, a reduction of 60 percent from the preliminary FIRM values. He assisted the City with their appeal of the FEMA preliminary FIRM. The revisions have been accepted by FEMA and will be included in the future map.

West Branch Alamo Creek Floodplain Study, Alameda County, CA
A floodplain study of the West Branch of Alamo Creek was performed for the Gale Ranch Development. The West Branch of Alamo Creek is a fairly small and narrow channel on a wide floodplain. The channel has emergent vegetation that has higher Manning’s n value than the drier adjacent overbank areas. The HEC-RAS computer model was used to model 2-year, 10-year, and 100-year flood flows. Comparison of existing condition flows and post-development flows were made to determine the impacts of the development on flooding and to identify potential locations for detention basins.

Collier Canyon Creek CLOMR, Livermore, CA
A storm water bypass consisting of parallel 72 inch diameter and 78 inch diameter pipelines was constructed for the Collier Canyon Creek in North Livermore. Dr. Lewandowski developed models for both the creek and the bypass pipelines for use in development of a CLOMR for the project. Channel flows were reduced by the bypass, causing the 100-year floodplain boundary to lie within the channel banks. The pipelines flows were modeled using PCSWMM, which allowed for partially full pipeline flow in the steeper sections of the parallel pipes. The natural creek channel was modeled using HEC-RAS, with flow boundary conditions developed on an iterative basis, depending on the flow rates in the bypass pipeline. Dr. Lewandowski worked directly with FEMA staff to finalize the modeling issues and resolve the CLOMR application issues.

Agua Fria Creek Relocation Analysis for Warren Avenue Grade Separation, Fremont, CA
Dr. Lewandowski was project manager for the hydraulic analysis of two large supercritical flow channels that were relocated to allow construction of a roadway undercrossing of a railroad right of way. Preliminary hydraulic calculations were performed to determine approximate slopes, channel widths, and superelevation at channel curves to prevent flooding at the 100-year flow rate. The channels were a combination of rectangular open channel and culvert flow. Transitions between the rectangular and existing trapezoidal channel and the junction of the two supercritical flows were designed to prevent formation of hydraulic jumps. A HEC-RAS model was developed to verify channel flow conditions and water surface profiles.

Mission Bay Development Flooding and Storm Drain Analysis, San Francisco, CA
Dr. Lewandowski was the project manager for hydraulic modeling of 100-year runoff and overland flows for portions of the Mission Bay project. He developed drainage scenarios and supervised the development of HEC-RAS models for sections of the development. Many of these models involved shallow flow depths in streets and limited discharge locations. Based on model results, the street designs and grades were modified to prevent water surface elevations from flooding the building footprint boundaries.

Agua Caliente Creek Floodplain Model, Fremont, CA
Dr. Lewandowski was project manager for this creek modeling study. A project site adjacent to Aqua Caliente Creek was planned for development, and the 100-year FEMA floodplain boundary was identified along the edge of the site. Dr. Lewandowski performed a hydraulic analysis of the existing creek using HEC-RAS to determine the approximate 100-year water surface for comparison to the finished elevations of the site. Preliminary drainage calculations for the project site were also completed to identify building pad elevations and approximate sizes of storm drains.

Home Depot EIR Hydraulics Review, Watsonville, CA
In development of the EIR for this project, Dr. Lewandowski performed review of the hydraulic calculations for drainage and water quality. He also developed a memorandum for the City recommending the value of the runoff coefficients that should be used in the project. He also wrote sections of the draft EIR and responded to public comments.

Southfront Road Trunk Storm Drain Analysis, Livermore, CA
Dr. Lewandowski was the project engineer for the analysis of a new trunk storm drain to replace the existing discharge into the Caltrans I-580 ditch and right-of-way. As-built drawings were reviewed and a SWMM model was constructed for the trunk drain to determine the required size and slope of each section of the storm drain.

Crystal Springs Reservoir Sedimentation Basin Predesign, San Francisco, CA
Dr. Lewandowski served as project engineer for the Upper Crystal Springs Reservoir sedimentation basin conceptual design. In this project, the Habitat Improvement Plan identified the previous sedimentation basin as future habitat for two endangered species. A new basin was relocated in a grassland area, and designed to collect sediments from the creeks discharging into the existing basin.

Drainage and Water Quality Studies, Los Angeles International Airport, Los Angeles, CA
These studies were completed as part of the CEQA/NEPA effort to determine impacts of the planned airport expansion. The potential for flooding created by the planned expansion was compared with the existing flooding at the airport. Dr. Lewandowski was project engineer for the drainage and water quality analyses.

San Elijo Lagoon Tidal Hydrodynamic Model, San Diego County, CA
Dr. Lewandowski has developed a hydrodynamic model for the San Elijo Lagoon, a 500-acre tidal wetland in Northern San Diego County, California. Model simulations included tidal flow movements under restoration scenarios selected to maintain natural tidal action in the lagoon. The software ESTFLO was used, and the code was reviewed and modified for model formulation. The project included delineation of wetland slough channels and heavily vegetated overbank flow areas. Vegetation resistance formulations utilized in the model were based on dissertation research. Existing field data was reviewed and implemented in the model calibration.

Storm Drain Modeling and Master Planning, Sacramento, CA
As project engineer, Dr. Lewandowski used the SWMM model to simulate storm water runoff for a 150-acre watershed comprising both open channel and conduit flows. He also char¬acterized and modeled alternatives to meet city standards for flood elevations in the street during the 10- and 100-year rainfall events.
Dr. Jeff Lewandowski, P.E., C 52503

Advanced Hydro Engineering

3082 Cafeto Drive, Walnut Creek , CA 94598

(925) 639-7053

E-mail Jeff Lewandowski : http://www.ahydroeng.com/

Dr. Lewandowski is a registered professional engineer in the State of California, and has 30 years of professional experience in water related systems analysis and modeling, including:

Drinking Water Systems
Wastewater Systems
Storm Drain Systems
Subsurface Drainage

His clients appreciate his strategic and practical solutions, his easy to understand explanations of project results and his attention to maintaining the project schedule and budget.