STREAM DYNAMICS IN A COUPLED HUMAN-CLIMATE-POSTGLACIAL WATERSHED

A river’s flow regime is defined by patterns of discharge over time. These patterns are governed by in-channel hydraulic routing conditions and runoff process controlled by the geologic, biologic, and climatic characteristics of the contributing watershed. Modifications to these conditions and consequent shifts in flow regime present a major challenge to the sustainability of water supply, water quality, and habitat diversity. Understanding the relations between climate, land cover, hydrology, stream channel conditions, and flow regime is the first step in the sustainable management of a system.

This research examines flow regime characteristics and sensitivity to watershed modifications in a major tributary to Sebago Lake in southern Maine, the Northwest River. Sebago Lake is the primary source of drinking water for ~15% of Maine’s population and, along with its contributing stream networks, is prized for aesthetics, aquatic habitat, and recreation. Despite extensive human interventions in the watershed’s post-glacial landscape over the past three centuries, the region remains predominantly rural and forested. However, this is projected to change to more extensive development in the area immediately surrounding the lake in future decades.

We examine the interactions between watershed conditions, surface flows, and stream channel conditions in the Northwest River system using a distributed watershed model. This model is used to evaluate scenarios defined by predicted land cover changes, hydraulic controls in the drainage network, and drainage network expansion. These scenarios represent a range of watershed and drainage network modifications observed to be predictably associated with human development. Model calibration and validation is performed using four years of discharge data recorded near Northwest River’s outlet to the lake, and the total water balance is used as an indicator. All scenarios result in alternations to flow conditions and the sub-basin’s total water budget. Future work will use these results along with detailed channel measurements to evaluate stream bed dynamics in response to human activities in the landscape.