Project: Hazel's Creek Drainage and Conservation Facility

Where: Spokane, WA

Overview

The South Hill region of the City of Spokane is a growing suburb that has experienced significant increases in stormwater runoff due to increased development. The area lacks a comprehensive stormwater collection, conveyance and management network, and the region’s geology limits opportunities for stormwater infiltration. However, in the northeast portion of South Hill at the Hazel’s Creek Drainage and Conservation Facility (HC Facility) a shallow stream called Hazel’s Creek disappears into the ground, indicating that the site has the potential to absorb additional stormwater. The City selected GeoEngineers to evaluate the site and assess whether the aquifer could help manage the area's stormwater.

Approach

GeoEngineers sought to determine where Hazel’s Creek goes when it disappears underground and if adding more stormwater to the aquifer would result in flooding or other concerns. To accomplish this goal, the project team needed to fully determine the size and shape of the aquifer underlying the site, which extends more than a mile from the HC Facility. The project team used a range of engineering and earth science tools and techniques to develop a detailed understanding of HC Facility and its short- and long-term infiltration potential. These tools and techniques included:

• Air rotary drilling
• Geophysical seismic refraction survey
• Hydrologic (surface water) instrumentation
• Geographic Information System (GIS) analysis
• Groundwater flow modeling

Using the collected data, the team developed a computerized groundwater flow model that:

• Defined the capacity of the site and aquifer to infiltrate and transport stormwater
• Analyzed where the additional groundwater would flow and how it would affect down-channel landowners
• Simulated the feasibility of proposed infiltration sites elsewhere in the area
• Identified potential flooding areas

Results

• GeoEngineers discovered a previously unknown drainage way under the site that has the potential to help manage the area’s stormwater runoff
• The project team developed an animated 3-D model of the aquifer, which helped the City communicate the project’s findings to City staff and stakeholders
• Techniques used in this study can be adapted for future feasibility evaluations of a wide range of sites in the Inland Northwest with similar geologic conditions

Facts

• This evaluation is the only stormwater infiltration project of its complexity completed in the Inland Northwest
• Bronze Award, 2010 ACEC Washington Engineering Excellence Awards
• Lead GeoEngineers office: Spokane, WA