Effects of in-stream large wood on shallow aquifer recharge at Indian Creek in central Washington

Restoration of streams and floodplains using large wood is now common practice in Washington. The primary goals are to restore aquatic habitat, and riparian ecosystems and reconnect streams to floodplains. A key factor for the success of these projects is to slow down the surface water so that it can filter into the ground to recharge the surrounding alluvial groundwater aquifer. This project investigates whether large wood piles recently placed in a stream channel have influenced shallow groundwater recharge at Indian Creek, a tributary to the North Fork Teanaway River in central Washington. In-channel large wood restoration began at Indian Creek in 2016. The methods and data necessary to complete this work are groundwater levels, floodplain stratigraphy, aerial imagery, and hydraulic stream modeling. Data loggers installed in monitoring wells across the floodplain have recorded groundwater levels from 2014-2020, before and after the in-channel wood restoration. Aerial imagery and modeling were used to assess differences in stream levels with and without wood at different flow rates. Model results suggest adding wood in stream can increase water on floodplain during the high flow season. The stratigraphy of the floodplain was described along the stream bank and using an auger. The upper 2 meters consists mainly of fine silt and clay. Manual groundwater level measurements show water within a sand and gravel layer beneath the clay layer. The widespread clay layer in the lower Teanaway watershed may impede vertical movement of the groundwater and could limit the recharge capacity of the shallow aquifer