Clear Creek Solutions Projects

Costco

Client: Costco Wholesale, Issaquah, WA

Costco's development of a new store in south Snohomish County, just north of Woodinville, required innovative strategies and analysis to protect adjacent Little Bear Creek. The Costco underground stormwater storage facilities reduce peak flows in Little Bear Creek.

The Costco store site is located on 14.38 acres between SR 522 and Highway 9. An additional 2.35 acres of Highway 9 improvements was planned along the store's frontage. Drainage from the site crosses SR 522 in WSDOT culverts and enters Little Bear Creek. The WSDOT permit required the Costco stormwater system to meet Department of Ecology flow control standards.

Doug Beyerlein used WWHM to size the two stormwater systems for Costco. On-site stormwater runoff (from the store and parking lot drainage) are routed to an underground storage facility consisting of 5240 linear feet of 96-inch diameter pipe (6.04 ac-ft of storage). The runoff from off-site Highway 9 improvements are directed to a separate underground storage system with 1140 linear feet of 96-inch pipe (1.31 ac-ft of storage). Both systems include 6 inches of dead storage for initial water quality treatment. Additional water quality treatment will be provided by Stormwater Management, Inc.'s Stormfilter units.

The stormwater runoff impact to Little Bear Creek was analyzed using HSPF and the Little Bear Creek watershed model developed by Mr. Beyerlein for King County. The proposed Costco land use conditions were modeled and compared with the existing land use (a warehouse facility and adjacent gravel auto yard). Stormwater runoff is reduced from 23 cfs to less than 1 cfs for the 100-year flood. Little Bear Creek peak flows are reduced by approximately 1%.

Clark County

Client: Clark County Public Works, Vancouver, WA

Clark County contracted with Otak to update the County's stormwater ordinance. As part of this work Clear Creek Solutions was hired to produce HSPF calibrations of two watersheds in the county. The calibrated HSPF parameter values were then used to update the Western Washington Hydrology Model (WWHM) for Clark County.

In order to employ HSPF as the hydrologic stormwater engine for WWHM, it must be calibrated to watersheds that reflect the range of climatic, topographic, soil, and land use conditions within Clark County. In this study, model simulations were performed for the Mill Creek and Gee Creek watersheds. Topographic, soils, and land use/cover information was used to develop the model segmentation and parameter inputs for the watershed models. Both quantitative and qualitative comparisons were performed to support the model performance evaluation effort.

Based on the model results, the HSPF application to the Mill Creek and Gee Creek watersheds provide a sound, calibrated and validated HSPF parameter values for Clark County. The resulting model parameter values are appropriate for use in WWHM, and for impact evaluation of flood control alternatives to meet the Washington State Department of Ecology's requirements. The calibration results, based on the weight-of-evidence approach described herein, demonstrate a good representation of the observed data. This is the outcome of a wide range of graphical comparisons and measures of model performance for flow duration and individual storm event simulations. These comparisons demonstrate conclusively that the models are a good representation of the water balance and hydrology of the watersheds.

New HSPF pervious land segments (PERLNDs) and calibrated parameter values replaced the standard PERLNDs and values used in WWHM for Clark County in support of the County's updated stormwater ordinance.

King County

Client: King County Department of Natural Resources and Parks, Seattle, WA

Joe Brascher and Doug Beyerlein of Clear Creek Solutions provided the King County Department of Natural Resources and Parks, Water and Land Resources Division with HSPF modeling services to develop a water quantity and quality analysis models for two topographic basins - the Green-Duwamish and the Lake Washington-Ship Canal basins. These models support the two major projects: the Green-Duwamish Water Quality Assessment (GDWQA) and the Sammamish-Washington Analysis and Modeling Program (SWAMP). They are integrated components of an overall modeling system of both watersheds and major receiving water processes including hydrodynamics, water quality, and bio-dynamics within the Duwamish River and Lakes Sammamish, Washington, and Union.

The primary purpose of the watershed water quality and quantity models is to support the GDWQA and SWAMP teams by simulating at a tributary level, surface and subsurface flow and associated physical, chemical, and biological loads to major receiving waters -- the Green River and Duwamish Estuary for the GDWQA and the major lakes for the SWAMP under a range of land use and infrastructure scenarios. Additionally these models provide a general tool for watershed analysis, management and educational outreach components of SWAMP and GDWQA, King County's ESA-response, aquatic resource protection, stormwater management programs, and ecological and human health risk assessment.

Wenatchee

Client: City of Wenatchee, WA


The City of Wenatchee SWMM modeling study determined conveyance system capacity and upgrades at various locations throughout the city's urban stormwater drainage network. The SWMM modeling was conducted by Mr. Joseph Brascher. Six different scenarios were modeled including both current and future land use conditions. SWMM was run on a continuous basis using 40 years of hourly rainfall data. Output from SWMM was then used to compute flood frequency information for each culvert in the drainage system network.

A total of over 1000 culverts were identified and modeled as part of the drainage system. Each culvert was evaluated for flood overtopping using both current and future land use information. Culvert sizes were upgraded to provide sufficient conveyance capacity where needed.

Fifteen separate SWMM models were constructed to simulate flood flows in the city's drainage system. For each model 40 years of hourly streamflow data were produced. Log Pearson Type III flood frequency statistics were computed from the SWMM simulated flow data. Simulated flow data were also used to identify how proposed flooding solutions would alter local and downstream flooding. This information was used to determine the benefits and costs of each solution.

Hydrologic Conditions Index Study, Washington Department of Ecology

Six watershed models were calibrated for the purposes of determining High Pulse Count (HPC) Coefficients. The HPC coefficients are used in the computation of the Hydrologic Conditions Index (HCI). The goal of the study is to produce generalized coefficients that can be used to compute existing and potential HCI values for watersheds in Western Washington.