Continued Field Measurement of Riparian ET, Lower Colorado River Basin
Project ID: 3484
Principal Investigator: Ian Ferguson
Research Topic: Water Resource Data Analysis
Funded Fiscal Years: 2013
Keywords: evapotranspiration, riparian, invasive species, long-term monitoring
Evapotranspiration (ET) from riparian and phreatophytic vegetation is an important component of reach, sub-basin and basin-scale water budgets in the Southwest, accounting for a significant fraction of non-agricultural ET in the region. Riparian vegetation also provides critical habitat for diverse communities of animal and bird species, including threatened and endangered bird species. Recent research has improved our understanding of riparian systems, including our ability to measure riparian ET via ground-based and remote sensing (RS) methods. However, the complex interaction between hydrologic, meteorological, and ecological dynamics of riparian systems remains a challenge to water, land, and wildlife managers in the Southwest.
Since 2005, Reclamation has conducted continuous field measurement of ET and groundwater levels at three riparian sites adjacent to the Colorado River at Cibola NWR. Measurements have been used to quantify water use by Tamarisk, a riaprian invasive species; to evaluate and compare various RS ET algorithms; and to verify RS-based estimates of riparian ET from the Lower Colorado River Accounting System (LCRAS).
This project will continue measurement of ET and groundwater levels in support of ongoing and future research efforts, including:
- continued ground-based quantification of riparian ET
- continued verification and improvement of RS-based riparian ET estimates
- evaluation of variability in riparian ET with respect to climate, hydrology, and vegetation conditions, including burn and regrowth.
- evaluation of biases in hydrologic models due to lack of groundwater and phreatophyte representation
- use of ET observations in hydrologic model calibration, in lieu of or addition to streamflow and groundwater observations
Maintaining these sites as a long-term monitoring stations will also provide a valuable resource for assessing climate and land use change impacts on riparian consumptive use.
Need and Benefit
Estimates of ET from riparian vegetation are an important input to environmental resources assessment and management, particularly in semi-arid and arid basins in the Southwest where riparian ET is a significant component of the water budget on reach, sub-basin, and basin scales. Throughout the region, accurate estimates of "the disposition of water once it is released from [a reservoir]"--including the amount of water loss from the river and shallow aquifer via riparian ET--is a critical in order to effectively manage river systems. In the Lower Colorado River Basin, for example, the Lower Colorado River Accounting System (LCRAS) is used to track and manage releases from Hoover Dam. In other basins such as the Mojave, Reclamation has used ET estimates to quantify the potential water savings from removal of riparian invasive species such as Tamarisk and Russian Olive.
Field-based measurement of ET is critical for developing, calibrating, and verifying remote-sensing and numerical methods used to calculate riparian ET estimates needed by water and environmental resources managers. In addition to use in planning and operations support, maintaining a long-term field site for monitoring of riparian ET will provide the observational data necessary to support a wide range of research activities. Key research topics include quantifying the impact of riparian vegetation on reach, sub-basin, and basin-scale water budgets; evaluating the impact of riparian ET on surface water-groundwater interactions; evaluating correlations between climate, hydrology, and riparian ET, including evaluating climate change impacts on riparian ET; and evaluating relationships between riparian vegetation density, riparian ET, and riparian habitat quality for habitat and wildlife management.
This project will support continued field-based measurement of riparian ET and groundwater levels at the USBR field site at Cibola NWR. Project methods and available data will be documented in Reclamation technical reports, and quality controlled data will be made publicly available and shared with the academic community. Project team will conduct outreach with regional and area office staff and university partners to identify research efforts and decision contexts that could directly benefit from project data. This project also supports scoping of future research effort to evaluate biases in hydrologic models due to their lack of representation of riparian and phreatophyte ET.