Maki Endowment

Project researcher: Erick Bandala

Project Summary:

The presence of per- and polyfluoroalkyl substances (PFAS) in water has become a significant public concern. Among PFAS, perfluorooctanoic acid (PFOA), a bioaccumulative contaminant, has been gaining attention because of its potential environmental and human health risks. PFOA was reported in a recent study by DRI in the Las Vegas Wash (LVW) with consequent health implications for 30 million residents in southern Nevada and the lower Colorado River Basin, which provides water supply to the southwestern United States. A variety of technologies showing promise for the removal of aqueous PFOA have been reported—including membrane systems, adsorption, and phytoremediation—with different results and technology readiness. Of these, adsorption is the most promising and practical due to its low cost and simple operation. Out of the different types of adsorbents tested (i.e., granulated activated carbon [GAC], ion-exchange resins, and clays), GAC has shown significant performance for PFAS removal from water. However, GAC has drawbacks (e.g., poor regeneration efficiency, slow kinetics, and a limited adsorption capacity for PFOA), creating a need for cost-effective materials with potential for full-scale application. This project proposes assessing the capability of calcium hydroxyapatite (CHM), an alternative adsorbent material that has shown potential for PFOA adsorption. This project centers on understanding the adsorbent characteristics and effects of water quality parameters on PFOA adsorption by CHM.

Project Researcher: Rishi Parashar

Project Summary:

Understanding the reach scale and seasonal behavior of water quality parameters in the Las Vegas Wash, including those related to indicator pathogen organisms such as E. coli and coliform bacteria, are crucial to ensuring the health and safety of people who rely on the Wash to augment the community’s Colorado River allotment from Lake Mead. At present, the Southern Nevada Water Authority (SNWA) have ongoing projects to assess the health risk posed by discharge of Wash water to Lake Mead, but they lack a predictive tool to determine the retention and transport characteristics of pathogens in the Wash. This is a problem worthy of investigation because the Wash is known to have several major zones of hyporheic downwelling and upwelling, and several weirs along the length influencing reach-scale hydrodynamics. Microorganisms continuously immobilize and resuspend during downstream transport because of various processes, including gravitational settling, attachment to in-stream structures, and hyporheic exchange and filtration within the underlying sediments. The complex flow dynamics occurring at the hyporheic interface invariably affect transfer of nutrients and contaminants from groundwater to the stream and back. We propose to apply a stochastic model with a memory function accounting for advective-dispersive motion, probability of immobilization, residence time distribution in mobile (water column) and immobile (sediments) zones, and literature derived pathogen inactivation coefficients to model the observed trend in spatial and temporal behavior of E. coli and coliform bacteria. The research results will help address broader scientific questions about variation in reach-scale retention and transport dynamics of pathogens for an urbanized stream with several in-stream erosion control structures, and more specifically inform the boundary conditions for pathogen levels to be included in SNWA’s risk assessment models. Because monitoring pathogens at a high frequency is expensive and time-consuming, the proposed research can be useful in generating spatially and temporally continuous concentrations, and for scenario analysis to provide a basis for water management in the Wash.

Project Researcher: Guo Yu

Project Summary:

In urban area, flood risks and impacts are no longer tied to the Federal Emergency Management Agency (FEMA)-defined floodplains. Despite not being in the 100-year flood zone, many homes in urban areas have experienced frequent flooding. There are three main barriers to understanding urban flood risks: a lack of knowledge about urban flood patterns, difficulties in modeling urban floods, and inadequate measurement of flood events. This study aims to address these gaps by using flood insurance and damage data, along with an improved hydrological model, to better understand urban flood risks in Las Vegas, Nevada, where flash flooding is a common occurrence. First, we will use flood damage and insurance claims data to understand the trends over the past five decades. Second, we will improve the capability of the WRF-Hydro model for urban flood simulation by adding flood conveyance systems and detention basins. Finally, we will integrate flood simulation, flood damage data, and parcel value to derive a regional-scale depth-damage curve, which will be further used to estimate urban flood risks for different recurrence intervals. The findings will help the public and relevant authorities, such as the Clark County Regional Flood Control District, to develop more effective strategies for mitigating future urban flood risks. The framework developed in this study can be adapted and applied to other major US cities.

Project researcher: Greg Pohll

Project Summary

The Nevada Environmental Response Trust (NERT) Site is located within the Black Mountain Industrial (BMI) complex near Henderson, Nevada, which was the site of industrial chemical production from 1942 to the mid-1990s. The site was originally used by the U.S. Government to produce magnesium for the World War II effort, and then to produce manganese dioxide, sodium chlorate, and perchlorate, ammonium perchlorate, and boron products after a change in ownership. After the production facilities were closed, on‐site environmental cleanup efforts were initiated in 1998 and are ongoing (NERT, 2015).

Perchlorate, both a naturally occurring and manufactured chemical, was first detected in the Lower Colorado River in 1997 and the sources were traced upstream to the Las Vegas Wash. The Las Vegas Wash discharges into Lake Mead, which provides drinking water for over two million people within the Las Vegas metropolitan area. Understanding the exact source of perchlorate is critical for developing effective mitigation solutions. This project will provide enhancements to an existing groundwater flow and transport model, which can then be used to design optimal remediation strategies that will effectively mitigate contamination in Lake Mead.

Currently, there is no federal drinking water standard for perchlorate. The Environmental Protection Agency (EPA) is developing a Maximum Contaminant Level (MCL) to address the environmental health concerns that perchlorate interferes with thyroid function. Although the EPA is continuing to review the toxicology data as a basis for the MCL, preliminary data suggest that the MCL may be set as low as 1-5 μg/L (U.S. EPA, 2012). This has significant implications for southern Nevada water resources because perchlorate concentrations in Lake Mead vary between 1-5 μg/L annually (Nevada Division of Environmental Protection [NDEP], 2014). Although three remediation systems were installed that are capturing a large percentage of the perchlorate mass that enters the Las Vegas Wash, groundwater perchlorate concentrations still exceed 50 μg/L at Northshore Road and have not decreased significantly since 2007.

The objective of this project is to assist NDEP and its associated contractors in evaluating and enhancing groundwater flow and transport models of the NERT Site. Desert Research Institute will achieve this objective by:

1. Reviewing the existing groundwater model(s) to understand its general capabilities and limitations.

2. Refining the model to accurately simulate all fluid and perchlorate fluxes to the Las Vegas Wash.

3. Providing guidance on how model uncertainty can be quantified and presented effectively.

References

Nevada Division of Environmental Protection (NDEP), 2014. Updates on Perchlorate Remediation, Black Mountain Industrial Area, Henderson, Nevada. Prepared by the Bureau of Corrective Actions for the Las Vegas Wash Tour, May 1, 2014, p. 24.

Nevada Environmental Response Trust Site (NERT), 2015. Fact Sheet, p. 5.

U.S. Environmental Protection Agency (U.S. EPA), 2012. Life Stage Considerations and Interpretation of Recent Epidemiological Evidence to Develop a Maximum Contaminant Level Goal for Perchlorate. Washington, D.C., p. 48.

Project researchers: Julianne J. Miller, Kevin M. Heintz, Richard H. French, and William J. Meyer

Project Summary

Standard statistical methods to determine flood discharges for specific return periods are not applicable to a majority of the watersheds in the arid Southwest because most of them are ungaged or have short periods of record. Therefore, rainfall‑runoff models, such as the US Army Corps of Engineers (USACE) HEC-1 model (USACE, 1998) are often used to estimate flood discharges in the arid Southwest. The Clark County Regional Flood Control District (CCRFCD) recommends using the HEC-1 model in the Las Vegas area to generate hydrographs, which are used to design flood facilities (CCRFCD, 1999). A common approach used to create synthetic hydrographs in the HEC-1 model is the curve number (CN) method. The CN method is heavily reliant on choosing one of three antecedent moisture conditions (i.e., AMC-I, -II, or -III), which are ranked from dry to wet based on the amount of rainfall within 5 to 30 days prior to a storm event. The CCRFCD (1999) requires an AMC-II condition be assumed—which is the most commonly assumed AMC (McCuen, 2001)—to conservatively design flood control facilities. However, San Bernardino County, California, has recently adopted a practice of assuming AMC‑I for some undeveloped areas.

This project will evaluate the historic runoff response in the Clark County area. It will also establish the effect of antecedent soil conditions with respect to flooding in undeveloped land in the arid Southwest.

The objectives of this project are:

• To identify the historical flooding events within Clark County using historical flood data collected from CCRFCD records.
• To research historical rainfall data by:
  • Reviewing rainfall data collected preceding the historical flooding event data available.
  • Associating an AMC value with the flood producing event (i.e., I, II, or III).
• To fit an empirical probability distribution to the AMC condition at the time of the flood event.
• To use incremented CN input into HEC-1(USACE, 1998) to establish a range of peak flow values as a function of varied CN values.
• To compare the simulated hydrographs with historical storms to evaluate if the CN values match AMC-I, -II, or -III and how they compare with the historical information.

Project Updates

A storm event in the Las Vegas, Nevada, area was modeled using the CN method by varying between AMC-I and -III. The selected case study was the July 8, 1999, storm event within the Flamingo/Tropicana watershed, during which intense rainfall caused widespread flooding that exceeded the 100‑year flood frequency. An HEC-1 model was used to predict peak storage values at a flood control detention facility based on interpolated rainfall, varied CN values, and previously reported basin lag and basin area inputs. Curve number values were incremented by five percent moving from the initial condition of AMC‑I to a final condition of AMC-III. Rainfall values were known at nine surrounding rain gages and were further interpolated to reflect precipitation at individual subbasins within the study watershed (Figure 1). Rainfall interpolation was performed using an ordinary kriging function, which weights surrounding known values to create an interpolated surface. Calculated peak storage values were compared with the actual peak storage value measured at a detention facility downstream of the watershed. This study found that although the prior conditions meet the “dry” category (AMC-I), the actual runoff response was best represented by a CN value 40 percent larger than the value assumed by AMC-I. Therefore, runoff in this case was most accurately modeled at an intermediate CN value between AMC-I and -II (Figure 2). This study confirms the CCRFCD assumption that AMC-II should be applied in hydrologic models to conservatively estimate peak runoff.

References

Clark County Regional Flood Control District (CCRFCD), 1999. Hydrologic Criteria and Drainage Design Manual, Las Vegas, NV.

McCuen, R., 2001. “Application of Curve Number Hydrology in Semi-Arid and Desert Environments.” Journal of Floodplain Management, Vol. 2, No. 2.

U.S. Army Corps of Engineers (USACE), 1998. Hydrologic Engineering Center, HEC-1 Flood Hydrograph Package User’s Manual, Davis, CA.

Project researcher: Greg Pohll

Project Summary

Currently, there is no federal drinking water standard for perchlorate. The Environmental Protection Agency (EPA) is developing a Maximum Contaminant Level (MCL) to address the environmental health concern that perchlorate interferes with thyroid function. This project will provide conceptual updates to a groundwater flow and transport model of the Nevada Environmental Response Trust (NERT) site. Specifically, the remediation system and deeper Muddy Creek Formation will be added to the modeling framework to determine if one or both are likely sources of perchlorate for the Las Vegas Wash. An updated groundwater model is needed to fully explore solutions to lowering perchlorate concentrations below 1-2 μg/L (the most likely value of the MCL).

The objectives of this project are:

• To investigate the importance of multiple hydrogeologic conceptualizations for the NERT site.
• Develop numerical models to simulate the conceptualizations that are deemed important for the simulation of perchlorate transport.

Project Updates

DRI was asked to develop a proposal for the Nevada Division of Environmental Protection (NDEP) to aid in the review and development of a flow and transport model for the NERT site. Therefore, this project will focus on additional hydrogeologic processes that were not included in the NDEP project.

In collaboration with the Desert Research Institute (DRI) GreenPower program, select Division of Hydrologic Sciences (DHS) faculty will participate in GreenPower’s K-12 education and outreach through the DHS Maki Water Green Box project. This project will include two parts: Green Boxes and K-12 classroom/teacher instruction. Faculty members who apply for these funds must complete all of the following activities for the salary time that is allotted in the project budget:

• Green Box development
• Teacher training
• K-12 classroom instruction

Green Boxes:

• Number of educators that used the Green Box
• Demographics of the schools that use the Green Box
• Number of students that used the Green Box

• Number of educators that attend the training
• Demographics of the schools where the educators teach
• Satisfaction survey of the presentation

• Number of students reached through instruction
• Demographics of the schools
• Educator satisfaction surveys of the instruction

Project researchers: Justin Huntington, Charles Morton, Britta Daudert, Matt Bromley, and Blake Minor

Project Summary

Mapping groundwater evapotranspiration (ETg) rates and the conditions of groundwater dependent vegetation in eastern and southern Nevada is important to estimate groundwater budgets and perennial yield estimates. This mapping will also provide a baseline for the continued monitoring of groundwater dependent vegetation as groundwater development occurs. Annual variations in ETg can be fairly large because it is a function of depth to groundwater and at-surface radiative and advective energy. Therefore, decades of ETg mapping is needed to estimate an ETg mean or median and variance that is statistically robust and represents the perennial yield.

Decades of ETg mapping is also needed to establish baseline conditions. Groundwater rights permit terms for large-scale groundwater development and exportation projects in Nevada often require detailed hydrological and biological monitoring plans. Permit terms require monitoring groundwater-dependent ecosystems before groundwater pumping begins and continued monitoring as groundwater development progresses. Recent advances over the last two years in cloud computing of Landsat satellite imagery and gridded weather data has provided an excellent and unique opportunity for developing web applications for long-term vegetation and ET monitoring using over 30 years of Landsat and gridded weather data. This project was developed based on the research done for the Maki project “Development of a Southern Nevada Evapotranspiration Monitoring Program using Remote Sensing.”  

Background

The objectives of this study are to use cloud hosting and computing capabilities to develop and implement numerous web applications to monitor historical and near real-time vegetation conditions, and report annual groundwater evapotranspiration (ETg) estimates for phreatophyte groundwater discharge areas in southern and eastern Nevada. The proposed study consists of two parts:

• To develop web applications using Google App Engine and Google Maps Engine linked to the Google Earth Engine cloud computing and environmental monitoring platform to provide users the ability to dynamically compute and download numerous remotely sensed and gridded weather data products including vegetation indices, reference ET, precipitation, and annual evapotranspiration (ET) and ETg estimates in the form of time series or spatial data.
• To provide an interpretation and summary of historical and baseline conditions of vegetation conditions and ETg estimates for major phreatophyte groundwater discharge areas in southern and eastern Nevada in the form of a report and GIS geodatabase.

Progress

Significant progress has been made on both main objectives. A demo version of the Google Earth Engine application has been developed that currently hosts Nevada phreatophyte areas and is able to display ETg estimates (Figure 1). More work is needed to compute a spatially averaged annual time series of ETg for each respective phreatophyte area, which is planned for the coming year.

The specifics of the work accomplished to get to the point of developing the Nevada ETg mapper are described below. It was decided that all phreatophyte areas within the entire state would be included rather than just the areas in eastern and southern Nevada.

1. Develop a spatial dataset to map out the phreatophyte extent/groundwater discharge boundaries in Nevada.

Historical Reconnaissance Series Reports and Water Resource Bulletins have provided detailed maps that describe the phreatophyte extent/groundwater discharge boundaries for many hydrographic areas (HAs) in Nevada. These reports represent vegetative/groundwater conditions from the past sixty years and they are now available to the public on the Nevada Division of Water Resources (NDWR) website. In addition to these older reports, we have obtained a more current report from the U.S. Geological Survey (USGS) and Southern Nevada Water Authority (SNWA) that delineates phreatophyte extent for many basins within the Humboldt River Basin (Berger, 2000) and eastern Nevada (BARCASS and SNWA reports). After converting all of the scanned maps from the reports into JPEG or TIFF files, the images were georeferenced within ArcMap. Using a topographic map from ArcGIS online and the Georeference Tool from the ArcMap toolbox, each image was assigned a spatial reference for further analysis.

Once the images were given a spatial reference, shapefiles were created for each basin using the Editor Tool from the ArcMap toolbox. Each shapefile has digitized boundaries that represent the phreatophyte extent or groundwater discharge boundary, depending on what was described in the report. For example, in Figure 2, a groundwater discharge boundary (in yellow) was digitized from a USGS report for Crescent Valley.

After each boundary was digitized, information from the map/report was put into an attribute table for that shapefile. Many of the maps from the reports are not strictly limited to just phreatophyte extents/groundwater discharge boundaries. Table 1 shows that there are multiple polygons within one shapefile’s attribute table. Some of the maps/reports go into great detail about the type of vegetation that is present in each polygon. This is very useful when trying to calculate ET because different vegetation types exhibit different rates of ET. For example, an irrigated alfalfa crop may have a much higher rate of ET than the sparse vegetation adjacent to it. Having these various plant covers/vegetation types separated from each other will be useful for future calculations.

The attribute table for the shapefiles is comprised of information relating to the type of vegetation, basin location, source of the spatial data, area (acres) of the polygons, and whether or not irrigated areas are within the groundwater discharge zone. If irrigated areas are outside of the discharge zone, they are excluded from the calculations because they are not technically contributing to groundwater evapotranspiration (ETg), and therefore they must be obtaining water from another source.

2. Modify boundaries from older reports to represent more recent surface and groundwater conditions.

Before modifications were started, the Merge Tool from the ArcMap toolbox was used to combine the phreatophyte shapefiles into one shapefile to make editing easier. This combined each basin’s boundary into one shapefile with one attribute table. Although phreatophyte boundaries from older reports are very useful for understanding the historical conditions of the basins, updating these boundaries to reflect the current state of the basins is important for monitoring groundwater-dependent vegetation over time. Updating these boundaries was completed using remotely sensed data, water-level data, and field verification. Visual modifications were performed within an ArcMap session using various types of aerial imagery, raster data, and point data. Some of these data were constructed by employees at the Desert Research Institute, whereas other data were obtained from other sources (e.g., water-level data from NDWR).

Two remotely sensed products developed from the Landsat archive—a Normalized Difference Vegetation Index (NDVI) and thermal imagery—were very useful for modifying these boundaries. The NDVI proved to be effective for identifying areas with high plant cover (e.g., irrigated alfalfa) as well as bare soil areas with no plant cover (Figure 3). The thermal imagery clearly showed the areas where evapotranspiration was occurring. The darker areas of the thermal imagery showed that evaporative cooling by phreatophytes was occurring in the valley lowlands (Figure 4). Images for both of the NDVI and thermal imagery were created for multiple years, which allowed us to observe the changes in vegetation cover over time.

Further modifications of boundaries were completed using National Agriculture Imagery Program (NAIP) imagery from the U.S. Department of Agriculture, a hillshade created from 10 meter digital elevation models (DEMs), and water-level data from NDWR.

The NAIP imagery is a high-resolution aerial imagery that is a useful basemap for visualizing how the land surface appears in real life. This true-color imagery is a great reference image because it makes it easier to visualize the actual land surface. For example, it can be used to identify landforms (e.g., elevated hills) or developed areas that should not be included as part of the groundwater discharge area. It is also useful for identifying vegetated areas at high resolution that would otherwise be invisible to the naked eye.

The hillshade is convenient for restricting the boundaries from higher elevation areas. Often times, when creating shapefiles from scanned images, accuracy is lost during the process of georeferencing the images. Many of the boundaries may drift into areas of higher elevation because the maps are not fully accurate after georeferencing has been completed. The hillshade allowed us to observe whether or not the boundaries extended into areas where phreatophytes are typically not present. Upland areas and alluvial fans are typically the borders of groundwater discharge zones, and therefore the hillshade allows us to observe where these are located in relation to our digitized boundaries.

The final dataset that was used to make modifications integrated the water-level dataset from NDWR, which provided an interactive map of water-level data for numerous wells within Nevada. Many of these wells are located in areas within or nearby the groundwater discharge zone. The water-level data was useful for identifying the borders of the phreatophyte extent. If the depths to groundwater exceeded acceptable levels for phreatophytes, then it was concluded that the particular area could not be part of the groundwater discharge boundary. Evaluating the water-level data generated some interesting questions about how to approach phreatophyte mapping. In some of the areas, water levels had changed dramatically postdevelopment.

To verify that many of these boundaries accurately delineate phreatophyte extents, field verification was completed for many valleys in central and eastern Nevada. Field verification consisted of driving around in a truck while using a GPS that was synced to ArcMap. Using this technique, we were able to observe where we were in relation to our digitized phreatophyte boundaries. Many boundaries were significantly modified after observing their current condition in the field. After finishing our fieldwork and making some final modifications, metadata was created for the dataset. The Metadata Wizard tool was downloaded from the USGS website and used to complete the metadata file. Within this XML file is information regarding how, when, and who created the data. The metadata also describes the type of information presented in the dataset and what kind of sources went into creating/modifying the dataset (e.g., previous Recon Reports, Landsat products, and processing steps).

After creating the spatial phreatophyte dataset, we coordinated with the USGS. The meetings with the USGS led to numerous discussions about how to approach the pre-/postdevelopment issue and it gave us a chance to compare both of our groundwater discharge boundary datasets. Trying to incorporate both pre- and postdevelopment conditions into one dataset does not seem feasible, and therefore we decided to focus on postdevelopment conditions for updating our boundaries. Because we were able to confirm the accuracy of the USGS dataset during our review, the USGS asked us to complete a full peer review. Reviewing the phreatophyte extent dataset consisted of assessing its accuracy, determining the integrity/completeness of the data, and reviewing the metadata file.

After much discussion with the USGS, we decided that the best way to approach mapping out the phreatophyte extent is to use a hybrid dataset composed of our boundary modifications with their original line work. The dataset from the USGS had very detailed line work of phreatophyte extent, whereas our dataset has detailed polygons that represent the various types of vegetation cover within these basins. Combining both datasets into a hybrid was the easiest way for us to have an accurate delineation of current vegetation cover and conditions.

3. Summarize historical ET rates, areas, and volumes.

Using the historical data from the numerous Reconnaissance Reports and Water Resource Bulletins is crucial for understanding baseline vegetation conditions and ETg estimates for phreatophyte groundwater discharge areas in Nevada. Monitoring the groundwater dependent ecosystems before and after groundwater development is very important for water management purposes. Previous statistics have been gathered into an Excel file to summarize the historical ET rates, areas, and volumes for numerous basins in Nevada (Figure 5). This allows us to compare the historical data to more recent estimates of ETg and phreatophyte boundaries for long-term monitoring purposes. Expanding the spreadsheet to include many more HAs within Nevada will be useful for having statewide baseline vegetation conditions and ETg estimates.

Future work

Expanding this dataset to every HA in Nevada is crucial for monitoring groundwater dependent ecosystems and estimating perennial yield accurately. To monitor these ecosystems, mapping the phreatophyte extent and ETg rates in Nevada is of vital importance. The variability in estimating ETg is high because groundwater conditions and vegetation conditions change annually. The work from previous reports does not reflect the current status of phreatophyte land cover and ETg estimates. To account for all of the changes that have occurred to these HAs in Nevada, we are proposing to report annual ETg estimates for phreatophyte groundwater discharge areas in southern, northern, and eastern Nevada. We will analyze the potential ET per HA, develop an extensive dataset of current phreatophyte boundary conditions, and run Google Earth Engine to estimate ETg using an approach recently developed by Beamer et al. (2013). We will then host the source data and results within the Nevada ETg mapper. This work will occur over the next two years and fund master’s student Blake Minor.

Researchers: Richard Jasoni, John Healey, and Markus Berli

Project Summary

The Colorado River supplies 86 percent of the water used in the Las Vegas Valley. With the current rate of water use, the Colorado River and its reservoirs, such as Lake Mead, may not be able to sustain the water needs of Las Vegas in the future. Therefore, efforts to further reduce water use in the Valley are underway. Golf courses and their irrigation systems remain one of the biggest water users, even though an increasing amount of irrigation water is treated effluent. For example, the Tournament Players Course (TPC) golf course in Summerlin uses 459,281,000 gallons of water annually, 80 percent of which is treated effluent and 20 percent is potable water.

Since 2013, the Desert Research Institute has been conducting a small pilot study at TPC with the goal of reducing the amount of irrigation water. This project builds on the pilot study to obtain a better understanding of the water balance between soil, vegetation, and the atmosphere at the TPC golf course. In spring 2015, atmospheric, plant, and soil instrumentation was installed at one site at TPC Summerlin to measure atmospheric, plant, and soil water fluxes. This project will collect data over a two-year period. During the second year of the study, the researchers will develop a state-of-the-art, process-based model to calculate evapotranspiration from the atmosphere-plant-soil continuum. The atmosphere, plant, and soil data will then be used to validate the model calculations. A simple irrigation equation will also be developed so that irrigation managers can plan daily irrigation schedules.

The objectives of this project are:

• To develop a processed-based model and an irrigation scheduling equation to better schedule irrigation frequency and duration at TPC Summerlin and other golf courses in the Las Vegas Valley using atmospheric, plant, and soil water flux data.
• To test leaf clips for the water needs of golf course grass and assess how the data can be applied to irrigation scheduling. 

Project researchers: Alex Lutz and Ken McGwire

Project Summary

This project will use Gravity Recovery and Climate Experiment (GRACE) satellite data along with ancillary climate and groundwater data to assess groundwater storage over the past twelve years in eastern Nevada and portions of western Utah. These data are important for managing water resources, which is especially critical in Spring Valley (between the Steptoe and Snake Valleys), where the Southern Nevada Water Authority (SNWA) was awarded groundwater rights and has purchased surface water and groundwater rights for potential future water transfers to southern Nevada. Understanding the effects of climate variability on groundwater storage is a critical part of water management for the Las Vegas Valley. The researchers will evaluate groundwater storage using modified GRACE satellite data. The information generated from this research will be added to a database for long-term monitoring and program building.

The objectives of this project are:

• To determine if seasonal and interannual climate changes can be observed in groundwater storage using GRACE satellite data.
• To evaluate if this remotely sensed data set can be applied in the generally data-scarce Great Basin and its potential application to other global regions with similar climates.
• To produce one peer-reviewed publication and develop ongoing communication with the Eastern Nevada Landscape Coalition (ENLC) and the White Pine County Water Resources Commission and participate in the annual ENLC conference.

Project researchers: Don Sada and Mark Hausner

Project Summary

Southern Nevada is one of the hottest and driest regions in the United States and over the past 20 years, it has been one of the nation’s fasting growing regions. As the population grew, groundwater use increased. As groundwater withdrawals increased, springs dried, which resulted in the extinction of the Las Vegas dace (Rhinichthys deaconi) and the Raycraft Ranch poolfish (Empetrichthys latos concavus), the endangerment of the Pahrump Ranch poolfish (E. latos pahrump), and the extirpation of other crenophilic species.

Southern Nevada is expected to become more arid with climate change. The combination of current stresses and increasing aridity suggests that groundwater levels will continue to decrease and that spring discharge will subsequently decline in many areas. Scarce water supplies stress freshwater ecosystems, but there is little understanding of the ecological effects caused by smaller reductions in spring discharge. This information is needed to determine the amount of groundwater use that is consistent with sustainable use. This study will integrate field surveys, benthic macroinvertebrate (BMI) habitat-use modeling, and physical hydrologic modeling to examine the thermal and ecological effects of incremental reductions in discharge on a Moapa Valley spring brook. This project will also provide additional insight into the effects of groundwater uses on spring ecology. Increasing demand for groundwater in southern Nevada has led to concerns about sustainable water-resource development and balancing groundwater withdrawals with the ecological benefits of existing flows. The results of this study will be relevant to groundwater use and spring system issues throughout North America’s arid regions.

The objectives of this project are:

• To quantify the environmental benefits of spring discharge and identify tipping points at which further decreases in spring discharge cause disproportionate negative impacts on spring brooks.

Project researchers: Sunny Grunloh and Clay Cooper

Project Summary

Aquifer storage and recovery has been used to meet water needs by storing treated water underground in wells during wet periods so that it can be recovered during dry periods (Figure 1). In the southwestern United States,water is treated with chlorine and stored in the aquifer via an injection well. However, when chlorine reacts with dissolved organic matter, it forms the by-products trihalomethanes (THMs). Trihalomethanes are the most common disinfection by-products found in chlorinated water and are linked to adverse human health effects. This project combined 31 well data sets provided by the Southern Nevada Water Authority, a chloride mass balance to adjust for dilution, calculated parameters, and estimated parameters to build a single, confined, homogeneous, and isotropic model to simulate THM attenuation.

The objective of this project is:

• To develop a numerical model of THM distribution surrounding a well during aquifer storage and recovery with data and physical and chemical processes that are pertinent to the Las Vegas Springs aquifer.

Project Updates

The recovery stage was modeled as a representation of the total trihalomethanes (TTHM) in drinking water that could be delivered to residents. The TTHMs refer to the four THM species: chloroform, bromodichloromethane, dibromochloromethane, and bromoform. The largest change in TTHM concentration at the dual-use well occurred during the first few days of recovery (Figure 2). The physical and chemical mass transport processes of advection, dispersion, and reactions with aquifer material all affected TTHM concentrations at the dual-use well.

A foundation simulation was the basis for the simulated TTHM movement and sensitivity analysis. The simulations included one dual-use well where injection and pumping (recovery) were each performed for 90 days, except in Figure 2 where pumping occurred for 180 days. The TTHMs were injected at a concentration of 0.1 mg/L. Advection, dispersion, source/sink mixing, and chemical reaction with aquifer material were present in the simulations. The sensitivity analysis included flow rates at the well, porosity, hydraulic conductivity, longitudinal dispersivity, and reaction rate. A longitudinal dispersivity (αL) of two meters (Figure 3) and a reaction rate (k) of -0.0018 1/d (Figure 4) resulted in the largest difference in the TTHM concentration reaching the dual-use well compared with the foundation simulation.

References

Leising, J.F., 2004. Chemical conditions in the primary producing aquifers and portions of the shallow groundwater system of the Las Vegas Valley in 2000. Southern Nevada Water Authority Report, Las Vegas, Nevada.

Project researchers: Seshadri Rajagopal, Yong Zhang, Charles Morton, Karl Pohlmann, and Matt Reeves

Project Summary

Pahrump Valley is the most heavily allocated groundwater basin in Nevada and contains over 10,000 domestic wells. The sole source of water within the valley is the underlying basin-fill and carbonate aquifers that provide water for domestic, agricultural, commercial, and public uses. Recharge to this aquifer system originates from infiltration of precipitation primarily in the Spring Mountains (see the study area map). Total pumpage in the basin has continuously exceeded the Harrill (1986) sustainable basin yield estimate of 19,000 acre‐feet per year since the mid‐1950s and annual aquifer withdrawals exceeded 30,000 acre-feet per year between 1960 and 1980. The continuous pumping of the aquifer system has led to severe declines in water table elevations, a cessation of flow from groundwater‐fed springs, and land subsidence throughout the valley. The strain on the groundwater resources of Pahrump Valley through unsustainable groundwater withdrawal rates due to population growth and climate uncertainty threatens the future viability of Pahrump’s water resources.

This project will develop a precipitation-runoff modeling system (PRMS) to compute annual recharge maps for the groundwater flow model and for use in the integrated groundwater and surface water flow model (GSFLOW) framework. An existing DRI modular groundwater flow model (MODFLOW-2000) will be modified for use with MODFLOW-NWT, a Newton formulation for unconfined flow and recalibrated using updated water levels and pumpage inventories. Comparisons of MODFLOW results using constant, stationary recharge and PRMS‐computed, non-stationary annual recharge maps will be used to address the majority of the proposed research questions, including the potential for spatial variability in sustainable basin yield for semiarid basins in southern Nevada. The PRMS and MODFLOW models will then be combined into the GSFLOW integrated model framework. Once calibrated, Global Circulation Model (GCM) projections of temperature and climate will be used as forcings to the GSFLOW model to evaluate the impacts of climate change on future recharge rates in the Pahrump basin aquifer system.

The objectives of this project are:

• To develop an integrated GSFLOW model that will serve as a water resources management tool for the Nye County Water District (NCWD), which will aid in developing a groundwater management plan for Nye County, and thus reduce the risk of Pahrump Valley being designated a critical groundwater management area.
• To enhance our understanding of groundwater resource availability predictions based on traditional approaches using constant, stationary recharge compared to those based on integrated models that include detailed simulations of hydrological processes and higher‐resolution, nonstationary climatic data. 
• To assess the sensitivity of water resources in semiarid basins to transient perturbations in precipitation and recharge. 
• To evaluate the management of southern Nevada water resources to maintain a sustainable basin yield.
• To assess the impacts climate change could have on groundwater recharge to the Pahrump basin aquifer system.

Project Updates

The Pahrump Valley MODFLOW model (originally in MODFLOW-2000) has been converted into MODFLOW-NWT (for a nonlinear solution of unconfined flow) and the model is undergoing recalibration. Recalibration includes correcting some of the model ground surface and water level elevations and monitoring well observations.

References:

Project researchers: Rose Shillito, Markus Berli, and John Healey

Project Summary

The potential for both flooding and fires in the desert is likely to increase under climate change conditions with important consequences for southern Nevada. Desert flooding and postfire runoff are unique flow events with conditions that are not necessarily captured by current runoff theory. Soil sorptivity, the capability of dry soil to absorb water, may be a critical parameter to improve predictions for these runoff events. However, little is known about the quantitative connection between sorptivity, infiltration, and runoff, as well as how sorptivity can be measured accurately and reliably. Sorptivity also depends on the soil-moisture status and, under burned conditions, on the degree of soil hydrophobicity, which frequently exists after a fire. 

The objectives of this project are:

• To establish experimental and analytical procedures to determine soil sorptivity in the laboratory and in the field. 
• To evaluate sorptivity as a parameter for quantifying postfire water infiltration into soils.

Project Updates

Laboratory analysis and computer simulations were used to develop analytical methodologies to determine sorptivity from infiltration curves under different initial and boundary conditions. Results showed that sorptivity was dependent on soil moisture content, as expected, but there were regular discrepancies between one-dimensional and three-dimensional methods. The infiltration behavior of soil affected by fire was also measured at the Red Rock Canyon National Conservation Area near Las Vegas, Nevada, after the La Madre Fire of 2011. The small fire was caused by lighting and featured the typical postfire polka-dot burn pattern of open-canopy wildfires. 

Red Rock Canyon after the La Madre Fire in 2011, which shows the polka-dot burn pattern that is typical for low-elevation, open-canopy desert wildfires on coarse, rocky alluvial soils (Shillito et al., 2013)Sorptivity was measured along a 2.4 meter transect under both burned and unburned Utah juniper (Juniperus osteosperma) trees, as well as in the unburned interspace. The data showed that sorptivity values under the burned tree were consistently lower than under the unburned tree. Although sorptivity values in the interspace between the trees were similar to the values underneath the burned tree, they exhibited a different pattern. These results show that there is a fair amount of spatial heterogeneity in soil sorptivity under burned and unburned conditions. 

Results to date indicate that the differences in pre- and postfire soil infiltration can be detected by sorptivity measurements. Tested numerical methods to determine sorptivity from early-time transient infiltration measurements have been developed. The analysis of infiltration data can physically and analytically relate sorptivity to hydraulic conductivity, a parameter used in event-based runoff modeling. However, the early-time soil infiltration measurement of sorptivity may be a more meaningful parameter for runoff prediction for the intense, short-duration rainfall events that are characteristic of southern Nevada. 

Final Report

For a copy of the final report, “Measurement of soil sorptivity under different soil moisture and water repellency conditions, please contact Nicole Damon Nicole.Damon@www-dev.dri.edu

Presentations

This project was also presented at the AGU Chapman Conference, “Synthesizing Empirical Results to Improve Predictions of Post-wildfire Runoff and Erosion Response” held in Estes Park, Colorado, from August 25-31, 2013.

For a copy of the conference poster, titled “Hydrophobicity Following Wildfire on an Arid, Alluvial Soil,” please contact Nicole Damon Nicole.Damon@www-dev.dri.edu 

References:

Shillito, R., A. Kalra, N. Twarakavi, and M. Berli, 2013. Hydrophobicity following wildfire on an arid, alluvial soil – Poster. AGU Chapman Conference-Synthesizing Empirical Results to Improve Predictions of Post-wildfire Runoff and Erosion Response. American Geophysical Union, Estes Park, CO.

Project researchers: Rina Schumer and Scott McCoy 

Project Summary

The relationship between poor water pressure and aquifer matrix stress in balancing the force imposed by an overburden is a fundamental concept in hydrogeology because it explains why excessive groundwater withdrawal has led to surface deformation and subsidence. In the Las Vegas Valley, groundwater withdrawal has led to cracks near preexisting faults and ground subsidence of more than six feet. Although local subsidence issues resulting from pumping are well-known, recently it has been determined that changes in surface mass (glaciers, surface water bodies) and groundwater withdrawal can affect regional fault motion and seismicity (González et al., 2012; Hampel and Hetzel, 2006). This can been explained by the unloading of mass from the crust affecting the vertical stress state of the lithosphere as induced flexure and rebound alters the horizontal stress (Hetzel and Hampel, 2005).

In 2012, the Nevada state engineer approved the withdrawal of 61,127 acre-feet of groundwater from Spring Valley, 5,235 acre-feet from Cave Valley, 11,584 acre-feet from Dry Lake Valley, and 6,042 acre feet from Delamar Valley in the counties of Lincoln and White Pine for transfer to the Las Vegas water system. The pumping will occur in the valleys between eastern Nevada mountain ranges that are bounded on at least one side by a listric normal fault that has been active with large earthquakes during the last 1.6 million years (Price, 2004). Therefore, it is important to evaluate if withdrawals of this magnitude will drive crustal unloading stresses to induce seismicity or motion in normal regional faults.

Although the effects of altering eastern Nevada surface hydrology and ecology have been a focus of environmental impact statements, the possibility of affecting fault slip rates and inducing seismicity has not. The technology to evaluate this possibility has been developed over the past decade and will provide a cutting-edge research project for a graduate student who will be trained with cross-disciplinary expertise in structural geology, rheology, and hydrogeology. The graduate student will use numerical simulations to address how much withdrawal is sufficient to cause changes in regional lithospheric stress fields that can lead to fault motion. The graduate student will be co-advised by Rina Schumer and Scott McCoy, who is a new faculty member (earth surface processes) in Geological Sciences and Engineering at University of Nevada, Reno. Dr. McCoy’s participation in the Graduate Program of Hydrologic Sciences will broaden the program’s expertise in hydrogeomorphology. A finite element model of the crust and lithospheric mantle will be used to evaluate the evolution of the regional stress field that is subject to a reduction of groundwater mass near the surface. Strain and slip rates under various mass reduction scenarios will also be evaluated. The critical withdrawal volumes will be compared with proposed extraction plans for eastern Nevada and an evaluation of the long-term mass reduction that pumping capture zones will create. The software package ABAQUS (Hibbitt et al., 2002) has been used in the past for similar applications and will likely be used for this project.

The objectives of this project are:

• To determine it the magnitude of groundwater withdrawal and the reduction of the hydraulic head within the large capture zones in eastern Nevada basins is sufficient to modify the crustal stress field and affect basin faults.

• To determine the time scale of structural response to a reduction in water storage.

References:

Project researchers: Brad Lyles, John Healey, Rick Susfalk, and Janis Klimowicz

Project Summary

The Nevada Integrated Climate and Evapotranspiration Network (NICE Net) is a statewide, long-term monitoring network of stations primarily located near areas of enhanced evaporation (agricultural areas and natural wetlands). The network installation was initially funded by the Nevada State Engineer’s Office, through the Bureau of Reclamation, to provide data for water resource estimates for agricultural interests and water resource researchers and regulators. Each station is equipped with the necessary sensors to compute potential evapotranspiration. These sensors include air temperature, relative humidity, wind speed and direction, and solar radiation. Additional sensors at each station are used to estimate soil water deficits for irrigation scheduling and estimating water balance components. These sensors include precipitation (rainfall only), soil temperature, soil moisture, and soil conductance (soil sensors are at three depths). 

This project will provide biannual site maintenance visits, installation of additional equipment, and database management. Bulk precipitation gages will be installed at all eight stations, which will provide better estimates of total precipitation, as well as stable isotope and chloride/bromide samples for future research. High precision GEONOR weighing gages for snow and rain will be installed at stations in eastern Nevada to more accurately quantify total amount, timing, intensity, and duration of precipitation events that are critical for groundwater discharge estimates. Quality control will be performed on preliminary data retrieved from the GOES satellite on a monthly basis and a more thorough quality assurance will be performed on the complete datasets manually downloaded from the stations after a site visit.

The objectives of this project are:

• To enhance our knowledge of the water resources in southern Nevada.

• To provide long-term monitoring of climate and evapotranspiration in southern Nevada.

• To maintain assets that are valuable to the state, DRI, and the community.

NICE Net station locations, http://nicenet.dri.edu/.

Project researchers: Justin Huntington and Charles Morton

Project Summary

The majority of permitted water rights in southern Nevada are for irrigation. Because most hydrographic basins are either fully or over appropriated in southern Nevada, future water supplies for municipal and industrial purposes (e.g., cities, solar power, and geothermal power) will likely be derived from acquiring irrigation water rights. Therefore, it is important for the Nevada Division of Water Resources (NDWR) to know the historical consumptive use of irrigated lands proposed for water transfer and if the new use is going to consume more water through evapotranspiration (ET) than what was consumed historically. Consumptive use can differ significantly due to crop type, crop stress, frost-free growing period, water and agronomic management, inefficient and non-uniform irrigation, water limitations, etc. Because of this variability, considerable uncertainty exists regarding the actual water consumption quantities associated with different types of vegetation, individual water rights, and land holdings. Groundwater ET from phreatophyte vegetation in southern Nevada is also largely unknown over longer timescales, but it is needed to develop perennial yield estimates used by the NDWR. Many scientific and water management studies require knowledge of the historical actual consumptive use and groundwater ET from phreatophytes, such as groundwater flow modeling, analyzing natural versus anthropogenic water level fluctuations, development and refinement of basin water budgets, resolving water rights protests, and negotiation and litigation. 

The objectives of this project are:

• To develop an automated framework for estimating remotely sensed ET from irrigated lands in southern Nevada for the entire Landsat archive (1984-present).

• To estimate ET from irrigated areas in southern Nevada for 2006 to 2011 using METRIC.

• To develop GIS databases containing METRIC derived ET estimates for the irrigated areas.

• To manage and post gridded ET maps, vegetation indices, and all other intermediate and final products on DRI’s newly developed Nevada Remote Sensing Web Portal for free public access and download.

Project Updates

The semiautomated scripts for estimating ET using METRIC from 2001-2012 in the Moapa and Mesquite area (eastern Landsat path) have been implemented, the first iteration of ET 2005-2011 in the Amargosa Valley area (western Landsat path) using Amargosa Farms as the focus study area has been estimated, and a GIS database of field boundaries for ET aggregation has been completed. The Maki Endowment funding has allowed the PIs of this project to promote DRI’s unique capabilities for estimating ET, which has successfully encouraged collaboration within DRI and built research infrastructure with NASA, USGS, BLM, and Google. Two research papers have resulted from this effort:

Liebert, R., Huntington, J.L., Morton, C., Sueki, S., and K. Acharya, 2015. Estimating Water Salvage from Leaf Beetle Induced Tamarisk Defoliation in the Lower Virgin River Using Satellite Based Energy Balance. Journal of Ecohydrology. DOI: 10.1002/eco.1623

Sueki, S., Acharya, K., Huntington, J.L., Liebert, R., Healey, J., Jasoni, R., and M. Young, 2015. Defoliation Effect of Tamarisk Biocontrol agent, Diorhabda carinulata, on Evapotranspiration and Groundwater Levels. Journal of Ecohydrology. DOI: 10.1002/eco.1604

This effort has also helped DRI develop a collaboration with Google. Google has recently partnered with DRI to develop a larger applied research program to map historical and current water use across the western United States using Landsat data (http://goo.gl/PRBv8V). As a parallel effort, DRI has developed ClimateEngine.org (pictured), a free cloud computing web application that allows users to process and analyze Landsat and MODIS data. 

Project researchers: Kumud Acharya, John Healey, and Sachiko Sueki

Project Summary

The eddy covariance tower installed at the field site of the lower Virgin River.The lower Virgin River is a tributary of the Colorado River system, which is a major component of the water budget of the southwestern United States. The Virgin River is one of the largest free-flowing river basin watersheds in the western United States. It flows through Arizona, Utah, and Nevada and drains directly into Lake Mead. The river’s relevance to each state is an important issue as rising population growth results in greater demands on a limited, depleting water supply. To compound the situation, the invasion of nonnative plant species along the lower Virgin River has inundated this region and reduced water availability.

Tamarisk defoliation has been occurring along the Colorado River and its tributaries since the release of Diorhabda carinulata (commonly known as leaf beetles) in 2001. Over the past few years, large-scale beetle populations have been established in the lower Virgin River and they eventually reached the Overton arm of Lake Mead in 2011. Their relatively rapid progress through the Colorado River Basin provides a unique opportunity to directly assess if the beetles provide any water savings that can be measured by a change in evapotranspiration (ET) as they migrate through the tamarisk groves. This data will provide crucial information on herbivory-induced changes to ET and any potential net water savings as canopies become defoliated before the beetles reach the lower Colorado River systems, which have hundreds of miles of thick tamarisk forests. This project has direct implications on water issues in southern Nevada and will provide valuable insights into other study locations along the lower Colorado River system as the beetles move farther south, as well as other watersheds throughout the southwestern United States.

The objectives of this project are:

• To quantify ET prior to and following episodic herbivory.

• To calculate the difference in ET before and after the beetles to gain insight into the potential water savings.

• To monitor the groundwater oscillations and correlate the data with any modification of ET rates due to defoliation.

• To understand the effects of beetle re-herbivory and its impacts on tamarisk groundwater consumption.

Project Updates

The beetles migrated into the Virgin River eddy covariance site and began tamarisk defoliation in June 2011. The defoliation occurred once in 2011 and twice in 2012. From May to September during 2010, 2011, and 2012, oscillations in groundwater levels showed diurnal fluctuations in the water table due to phreatophytic groundwater consumption. A reduced magnitude (dampening) of the diurnal fluctuations that corresponded to the beetle defoliation was observed once in 2011 (June 24 to August 16) and twice in 2012 (May 22 to June 20, and July 27 and August 14). 

In 2011, daily ET was substantially reduced by the beginning of July, but it gradually increased until it was approximately the same or slightly higher than the 2010 daily ET by September. This showed that the tamarisks had recovered from the defoliation. The ET reduction was not as substantial in 2012 as it was in 2011, but it did occur twice and the second reduction was more substantial than the first. Widespread defoliation took place in midsummer in 2011, when there was a large amount of healthy foliage to sustain the expanding beetle populations. The first defoliation event in 2012 occurred in early spring when the tamarisks had just started establishing healthy foliage, which meant that there was less foliage for the beetles to consume. Therefore, it is likely that beetle populations could not increase to the size experienced in 2011. However, the tamarisk quickly refoliated and the second defoliation occurred in late summer of 2012 before the beetles started overwintering.

The majority of fire research to date has focused on the negative impacts of large, medium-to-high intensity burns, which typically cause massive combustion of litter and organic matter in the topsoil followed by increases in soil erosion, runoff, and loss of nutrients. The positive role of fires in vegetation succession and nutrient cycling also is well recognized. In contrast, low-intensity burns (with a soil temperature of < 220 degrees C) are presumed to cause minimal soil degradation and landscape/ecosystem alteration. As a result, there has been only limited research investigating potential negative consequences of such burns, although they account for almost half of total burned areas in the United States. Furthermore, climate change is expected to increase the frequency and area of land exposed to such low-intensity burns. Recent long-term studies on the effect of low-intensity fires on soil structure, however, are revealing that substantial loss of soil aggregate stability and porosity occurs several months to a few years after the burn has occurred. These degradations in soil structure often are followed by reduced infiltrability and increased soil erosion. The overarching goal of this proposed research is to investigate the impacts of low-intensity fires on soil structure and the implication for soil hydrology, erosion, and nutrient dynamics. Specifically, this project is designed to test three hypotheses: a) soil structure deterioration is caused by micro-scale stresses created within aggregates due to rapid vaporization or thermal expansion of soil particles as well as preferential volatilization of mostly hydrophilic simple organic molecules; b) disaggregation and subsequent surface sealing result in reduced infiltration and increased erosion; and c) preferential mobility of nutrient-rich dislodged fine aggregates and particles results in accelerated loss of nutrients and carbon via lateral and vertical transport. The proposed research will be conducted using soil samples collected from arid and semiarid ecosystems in eastern Nevada and will mimic characteristics of past low-intensity burns of the region.

Improved understanding of how low-intensity fires can lead to land/ecosystem degradation will benefit society by enabling more effective design of controlled burns as well as postburn land management practices. This knowledge also can play an important role in planning for mitigation of the effects of low-intensity fires in sensitive ecosystems and landscapes of arid/semiarid regions that are expected to experience more fires as a result of climate change. This research will expand ongoing collaboration with the Bureau of Land Management, thereby facilitating adoption of new advances to support science-based resource management. In addition, this project will provide educational and advanced research training to one PhD-level student and one postdoctoral researcher. Science boxes will be employed to engage K-12 students in the results of the proposed project.

NSF-EAR Grant No. 1324894

UNLV News Center Highlight: “The Trickle-Down Effect”