ABSTRACT:

In the western US, major landscape modifications for flood conveyance and conversion of floodplains to crops have reduced the natural pathways of recharge and groundwater discharge. Combined with direct flow diversions for irrigation, these modifications result in depleted streamflows during the critical summer low flow period. Depleted streams are much more susceptible to extreme spatial and temporal temperature variability, which is inextricably linked to aquatic habitat suitability. However, in depleted streams, even small amounts of colder water (e.g., cool lateral inflows) can moderate temperatures and provide critical thermal refugia. While irrigation diversions reduce the amount of water instream, seepage from nearby irrigated areas and canal networks can enhance baseflows and moderate stream temperatures downstream of diversions. Some rivers now depend on these human-mediated return flows to maintain suitable flow and temperature conditions for river ecosystems over the dry season, making them sensitive to changes in land and water management. To improve our understanding of the role of irrigation diversions and shallow return flows on stream temperature patterns, we collected flow and temperature measurements along a diversion-depleted reach of the Blacksmith Fork River in northern Utah over three summers. We determined the significance of site-specific properties (shading, weather), channel morphology, and lateral inflows on spatial and temporal stream temperature patterns. We found that lateral inflows, most likely sourced from unlined canals, were a critical component for maintaining suitable river temperatures. This study informs local and regional water management efforts during low flow periods and highlights potential unintended consequences of irrigation efficiency projects that reduce seepage.

ABSTRACT:

This project used Budyko-based methods to determine the elasticity and sensitivity of 29 subbasins in the Colorado River Basin. Elasticity and sensitivity are metrics used to determine the relative expected changes in runoff given changes in precipitation and temperature, respectively. We used publicly available data to determine long term averages for temperature, precipitation, and runoff for principal Colorado River subbasins. Given those data, we used Budyko-based methods to estimate the elasticity and sensitivity of each subbasin to changes in temperature and precipitation. We determined the aridity index of each subbasin and Budyko parameter (w), which aggregates watershed storage characteristics. Subcatchments located in the Upper Basin, driven mostly by snowmelt, have a lower aridity index and higher w value than those in the Lower Basin, driven by monsoonal storm events. The Paria and the Little Colorado River subbasins are particularly sensitive to changes in precipitation and temperature. To identify the initialization of direct human impacts, we used a double mass curve break point analysis on a single subcatchment. Two breakpoints were identified, 1963 and 1988, corresponding to human impact and climate change, respectively.

This data resource includes a document and power point reporting the key findings of this work. We include the code, input, and output files used to perform analyses, all of which are described in the readme.

ABSTRACT:

Since the closing of Glen Canyon Dam, the clear waters of the Colorado River have stripped sediment from beaches and sandbars in the Grand Canyon. In an attempt to distribute sand to rebuild beaches, high flow experiments (HFE) have been conducted wherein large releases from Glen Canyon Dam are made over several days. The HFE events are timed to follow the summer/fall monsoon season when sand delivery from the Paria River is typically high given that the Paria is the primary source of sand to the Colorado River in Marble Canyon. Unrelated reservoir operating rules coordinate annual releases from Lake Powell so that the storage contents of Lakes Powell and Mead are equalized. If these “equalization flows” are released when there is relatively little sand supplied from the Paria River, they are likely to erode downstream sandbars, including those created by HFEs. Currently, there is no connection between the operations for reservoir equalization and for implementation of HFEs. Our analysis examines potential changes to the equalization protocols to explore whether equalization flows can be delayed to avoid releases that cause sandbar depletion. Results indicate that delaying equalization in favor of sediment supply results in some inequity for Lakes Powell and Mead, but the imbalance is less than anticipated and less than with no equalization present. Jointly considering sediment supply and equalization could help retain sediment within the Grand Canyon, however, even in years of sand load that meets the threshold for HFE experiments, the sediment supply may not be sufficient to balance out the volumes of equalization flows.

This data resource consists of the files used to support this work. The word document and the power point presentation present the results of this work. The folder CRSS contains two other folders. One folder, 'model' contains a saved version of the Colorado River Simulation System - a model that may be implemented in Riverware. This saved model includes slots corresponding to estimated sediment and slots generated by the implemented ruleset to govern equalization (Sediment Equalization Trigger, Years Without Sediment, 1-yr, 2-yr, 3-yr Equalization Delay). The 'ruleset' folder contains rulesets used in this analysis. There are four rulesets - each corresponding to scenarios run. The folder Data contains R code for running statistical analysis on input sediment data and flow data. The raw input files to run the code are included that correspond to natural flow inputs(obtained from the Bureau of Reclamation) and sand load from the Paria River (obtained from the Grand Canyon Monitoring and Research Center). The Results folder includes 1. a table of Estimated Summer Sandload and 2. a spreadsheet of CRSS results for the various scenarios run along with plots for comparing between them.