USGS Grant Number: G16AP00196
Year Established: 2016 Start Date: 2016-09-01 End Date: 2019-08-31
Total Federal Funds: $249,625 Total Non-Federal Funds: $250,783
Principal Investigators: Rosemary Carroll, Rina Schumer, Christopher Green
Abstract: The Colorado River is a major water source and economic engine for seven Western U.S. states. The majority of its water originates in snow-dominated headwaters. These headwater basins are considered especially vulnerable to climate change with implications for water resources and environmental management. This study will be the first to apply new methods for developing streamflow time-varying travel time distributions (TTDs) to a snow-dominated watershed and, in particular, at a scale relevant for water management decisions (>100 km2). Proposed work will develop TTDs describing the length of time water and solutes spend in the watershed under various hydrologic conditions using environmental tracers that capture a wide range of travel times. TTDs reflect integrated effects of watershed compartment connectivity and the degree of mixing of water of varying age since entering the watershed. These distributions affect water quality because many weathering processes and biogeochemical reactions are time-dependent. Time indicates catchment memory of past inputs and can be used as a proxy to understand hydrologic sensitivity to land use and climate change. We will address the functional form of storage-dependence in snow-dominated systems by testing both time-invariant and variant functional forms for goodness-of-fit to observed concentrations and power spectral density. We will augment and leverage Lawrence Berkeley National Laboratory Science Focus Area's on-going environmental data collection within the East River located in Gothic, CO; as well as their physically based, fully integrated surface water-groundwater model of the site (ParFlow.CLM). Hydrochemically derived TTDs will be compared to those generated from Lagrangian particle paths derived from highly resolved pressure fields produced by ParFlow.CLM. The numerical model will be used to describe the physical basis of hydrochemically derived TTDs and allow a sensitivity analysis based on ranges in temperature, precipitation and vegetation to investigate thresholds related to travel time moments. Seasonal TTD moments will be correlated to hydrograph characteristics, as well as flux of dissolved solids, carbon, nutrients and metals. While the proposed work focuses on an intensively studied, pristine watershed for proof of concept, we lay out a framework for the generalization of results and transferability to other systems in the region. Additionally, we will work with local and regional water managers in the Upper and Lower Colorado River Basin on methods to incorporate results into adaptive management planning.