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Hydrology & Hydraulic Modeling & Assessment

Steady Flow, Unsteady Flow, Sedimentation, Watersheds, Meteorology, Surface Runoff & GIS

Listed below are many of the projects we’ve completed for our clients over the years. We’ve chosen to focus and expand on several key examples which are highlighted in blue. Clicking on those projects allows you to view in-depth what services NCI provided as well as details on the project itself.

Las Gallinas Creek H & H Coastal Analysis

Marin County, CA

NCI performed and analysis to develop the riverine and coastal floodplain maps for the without project existing (year 0) condition and the without project future (year 50) condition. The performance of the flood control project was also evaluated using the risk and uncertainty method.


The tasks performed for the H&H analysis included: collecting and reviewing the hydrological and hydraulic data, tidal stages, and topographic/bathymetric data; developing a Digital Elevation Model (DEM) by merging the channel cross section survey and the levee profile survey into the County’s DEM; developing a HEC-RAS model for the South Fork of Las Gallinas Creek and adjacent floodplains, with the geometric data being derived using HEC-GeoRAS; conducting riverine hydraulic modeling and floodplain delineation using the HEC-RAS and HEC-GeoRAS models, and developing riverine floodplain maps for eight flood events for both the year 0 and the year 50 conditions; estimating uncertainties in water surface elevations considering the uncertainties in HEC-RAS model parameters; computing the conditional non-exceedance probabilities for the 100-year flood event; and evaluating the project performance based on the freeboard requirements for the 90% or 95% probability of non-exceedance.


The tasks performed for the coastal analysis included: conducting tidal statistic analysis, and deriving tidal frequency curve for the project site; estimating sea level rise based on the historic trend and on the USACE guidance (EC 1165-2-211), and developing the resulting tidal frequency curve in year 50; conducting wave hindcasting and determining return wave conditions in San Pablo Bay; determining wave conditions at the project site by transforming waves from the Bay to the site and by including the local wind waves generated within the marshland; computing wave runup, wave overtopping rate and cumulative water volume for eight coastal storm events considering the difference in levee characteristics; and determining the coastal inundation water levels, and developing the coastal inundation floodplain maps for eight coastal storm events for both the year 0 and the year 50 conditions.



Las Gallinas Creek H & H Coastal Analysis Las Gallinas Creek H & H Coastal Analysis

Guadalupe River Risk & Uncertainty Analysis

Santa Clara County, CA

The purpose of this risk and uncertainty analysis is to evaluate the project performance for the implemented Lower and Downtown Guadalupe River Project and for the proposed Upper Guadalupe River Project. The HEC-RAS and HEC-FDA models were used in this analysis. Both the existing conditions with the Lower and Downtown Guadalupe River Project, and the proposed Upper Guadalupe River Project design plans were investigated.


The three bypass projects in the downtown area of San Jose were incorporated into the existing HEC-RAS models for Guadalupe River. The new models were calibrated using the data from the physical models. The normal (50% probability) water surface profiles along the river were predicted using the new HEC-RAS models. The variation ranges of the water stages were computed by adjusting the model parameters, from which the standard deviations of the stage-discharge uncertainties were determined. Using the computed stage-discharge relation with the standard deviation of error and the discharge probability function with the statistical uncertainty, the HEC-FDA model was used to compute the conditional non-exceedance probabilities for the 100-year flood event. The project performances for the implemented projects and for the proposed project alternatives were evaluated based on the freeboard requirements for the 90% or 95% probability of non-exceedance in the 100-year flood event for the floodwalls, levees and incised channels, respectively.



Guadalupe River Risk & Uncertainty Analysis Guadalupe River Risk & Uncertainty Analysis

San Francisquito Creek Hydraulic Modeling & Floodplain Mapping

San Francisco, CA

The purpose of this study was to produce and/or update the existing floodplain mapping along the San Francisquito Creek from HWY 280 to the San Francisco Bay. An unsteady HEC-RAS model was developed based on the steady model. By applying the flow hydrographs and representing the potential flow breakout locations as lateral structures, this unsteady model was able to predict the flow breakout from the creek during the extreme flood events and would predict the flood conditions along the creek more realistically and more accurately.


The unsteady HEC-RAS model was re-calibrated using three historical flood events. After the coincident frequency analysis (CFA) was performed by the Corps, this model was further revised, with the downstream boundary condition being updated with the water stages determined in the CFA for the index station. The flow condition for the San Francisquito Creek was predicted with the revised unsteady model for eight flood events with the return periods of 2, 5, 10, 25, 50, 100, 250, and 500 years. The breakout flow hydrographs at all the breakout locations along the creek were determined based on the model results, and were input into the FLO-2D model as inflow hydrographs. The floodplain modeling was then conducted using the FLO-2D model, and the floodplain maps were generated in ArcMap.



San Francisquito Creek Hydraulic Modeling & Floodplain Mapping San Francisquito Creek Hydraulic Modeling & Floodplain Mapping

San Joaquin Marsh Enhancement, Phases I and II

Irvine, CA

San Joaquin Marsh is a fresh water marsh that is managed as part of the University of California Natural Reserve System. The purpose of the Phase I Enhancement was to provide a reliable water source to a series of managed ponds to promote native marsh habitat. Noble Consultants was responsible for the planning; permitting; investigation; surveying; design; cost estimation; and preparation of plans, specifications, and contract documents for improving approximately 40 acres of historic wetland. Design services included civil, electrical and mechanical engineering, and landscape architecture. Construction oversight was also provided. The California State Coastal Conservancy funded this work. The project components included removing invasive plant species; grading twelve ponds to provide a setting for a range of native plant species; improving existing internal levees; constructing a pump station and a pipeline system to provide water to all of the ponds; installing water control structures; and planting native species.


Phase 2 of the San Joaquin Marsh Enhancement Project involved recreating the historic hydrology of the marsh by improving the infrastructure for routing and delivering water throughout the area adjacent to the managed ponds that were enhanced in Phase I. Noble Consultants was the prime consultant responsible for the project, under contract with the University of California, Irvine for Phase II while for Phase I work Noble Consultants was under contract to the California State Coastal Conservancy. Work for this phase involved surveying, planning, permitting, design, and preparation of contract documents. The design services included civil, electrical, and mechanical engineering, and wetlands design. Project components included excavation to provide channelization for water distribution; excavation to create a muted fresh water marsh connection to the creek; construction of a pipeline through a flood control levee; construction of a pipeline from an existing well to supplement creek water; and improving existing levees.



San Joaquin Marsh Enhancement, Phases I and II San Joaquin Marsh Enhancement, Phases I and II
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