Scott Groce
Pierce County Planning and Public Works
Shuhui Dun
Pierce County Planning and Public Works
Tom Kantz
Pierce County Planning and Public Works
Timothy Hagan
Pierce County Planning and Public Works
Carol Falkenhayn Maloy
Pierce County Planning and Public Works
Since 2017, Pierce County Surface Water Management has been working on intensively monitoring Clover Creek to better understand spatiotemporal dynamics of water quality in the creek.
Clover Creek is in the very permeable glacial recession outwash deposit areas of Pierce County, WA.
Several reaches of the creek are on the WA impaired waterbodies list due to excursions of temperature, dissolved oxygen (DO), pH, and bacteria beyond water quality criteria.
This past summer (2022), a normally summer dry reach (a losing reach) of the creek was flowing due to a construction project discharging groundwater at river mile RM5.77 for dewatering. Along two-mile downstream of this discharge, DO increased from 10.2 mg/L (92% saturation) at RM5.77 to 15.4 mg/L (147% over saturation) at RM4.84, and then decreased to 2.5 mg/L (26% saturation) at RM3.88.
A similar pattern of DO increasing to super-saturation followed by extremely low concentration was observed along the creek in previous years.
Considering the simplified condition with a single water source, an in-depth study was carried out during 8/31/2022-9/6/2022 to illuminate reasons of DO spatial pattern along Clover Creek. Instantaneous stream discharges were measured at five monitoring stations from RM5.77-RM3.88, and water samples were collected from those stations for nutrient (nitrogen and phosphorus) concentration values.
Observed data show algae growth is playing a major role along the DO increasing reach, and wetlands/organic matter decomposition is dominating the DO decreasing reach.
A conceptual model for DO spatial changes is built based on the observed data to aid further data collection and water quality modeling for the upcoming TMDL (Total Maximum Daily Load) alternative projects.