Riverview Park Master Plan

Kent, Washington

HWA was contracted by J.A. Brennen Associates to provide geotechnical design and stormwater infiltration evaluation for park improvements, including parking, water access and other amenities. Included in the geotechnical evaluations of the proposed development was a mounded landscape and trail feature within the park and adjoining the active channel of the Green River. Stability of the riverbanks was assessed in respect to the design and construction aspects of this feature.

Porous paving for stormwater infiltration was under consideration for two locations; the parking lot and the turnaround. Rain gardens for stormwater treatment and infiltration were also designed adjacent to conventional concrete pavement on the access drive and pedestrian plaza. Soils at the site are predominantly low permeability alluvial deposits consisting of silts and silty sands. HWA evaluated locations proposed for on-site subsurface infiltration facilities.

HWA reviewed previous geotechnical and infiltration studies performed at the site and conducted additional site explorations, including test pits and laboratory soil testing to determine soil grain size distribution. Because of the low permeability soils, infiltration evaluations based on grain-size determination alone did not identify site soils to be suitable for infiltration. However, based on field observations of soil characteristics and our experience with similar soils in the region, HWA recommended conducting in-situ infiltration assessments via two modified pilot infiltration tests (PITs) at the site. Infiltration rates determined by the PITs were significantly higher than those provided by laboratory testing, and on-site infiltration was found to be feasible for the proposed development.