By
Mark Hill, Watershed Scientist
Climate change, a 20+-year mega-drought in the Southwest and disappearing Colorado River water raises the specter of insufficient water to support our cities and towns as well as agriculture throughout the lower Colorado Basin. More specifically, what is the water situation in Mesquite? Most of our water currently comes from groundwater pumping of an aquifer – Basin 222. How much water is in the aquifer? How is the aquifer recharged? Will pumping exceed recharge? How much more development can be sustained in Mesquite before our water supply is not sustainable?
The Virgin Valley Water District (VVWD) and the State Water Engineer will not address these questions directly, but loudly insist that there is enough water. They base their conclusion on a 1968 US Geologic Survey study and will not recognize the need for up-to-date data ignoring the fact that since 1968 there has been the worst drought ever experienced in the Colorado River drainage system, agriculture demand and spigot irrigation has increased throughout the watershed, municipal development has dramatically increased water demand for residential and industrial uses. So, to insist that a study from 1968 is reliable and adequate to manage water extraction from Basin 222 today ignores all the reasons why this is bad management.
Why is it that all other communities surrounding Mesquite are experiencing water shortages or planning for future shortages? St. George is advocating for a dam on the North Fork of the Virgin River to meet its present and future water needs. Cedar City is proposing to pump water from valleys outside the county. The Santa Clara City Council passed extensive water conservation and landscaping additions to its zoning codes that, among other items, limit the size of lawn areas at new homes, place water limits on new car washes and golf courses, bans certain plants and trees and prohibits irrigation with drinkable water from 10 a.m. to 8 p.m. from June to August. The city of Ivans followed suit. Las Vegas and Henderson just passed ordinances that greatly curtails lawn and other residential watering. Yet, in Mesquite all is well. To quote the CEO of the VVWD…” How many times to I have to say it? We have plenty of water![1][i]” Do we?
The Virgin Valley Water District (VVWD) manages and delivers water to Mesquite. Past studies, like the 1968 USGS study, have shown the annual perennial yield from the Basin 222 is about 3,600 ac-ft[2]. The VVWD is pumping over 7,000 ac-ft annually but claims to have a water budget of 12,271 ac-ft set by the state water engineer. This is misleading because the state engineer has set a water budget of 3,600 ac-ft for the VVWD. The 12,271 ac-ft reflects the number of over appropriated water rights for the basin.
Without the data from a legitimate conjunctive study[3] to determine an accurate perennial yield from the aquifer, we are all flying blind and simply making guesses. Is this sustainable or is VVWD “mining” the aquifer to meet increasing water demand from development in Mesquite.
The 2020 VVWD Master Plan does not specify the average perennial yield from the aquifer, nor does the plan address the issue of potential “mining” of groundwater, i.e., extracting water at a higher rate than recharge. The Plan states: “For the purposes of this study, it has been assumed that the groundwater aquifers have sufficient capacity and recharge, or “wet water”, to match the volumes allocated in the District’s “paper” water rights. This assumption is supported by the fact that District staff has reported that the majority of wells can operate at peak pumping rates for extended periods of time without causing continual drawdown (lowering of the water table around the well) in the aquifer”. This assumption is based on anecdotal observations, not data, not actual measurements. What is meant by the majority of wells? Does that mean a minority of wells do lower the water table? What is meant by extended periods of time? Days, weeks, or hours? How long does it take to recharge the water table?
In addition to this broad, unsubstantiated assumption, the plan ignores several important factors that could very well reduce the availability of “wet water” in the future.
The Bureau of Land Management has specific management policies for riparian habitat (stream side vegetation) including restoration and enhancement. The interaction of surface water and groundwater creates and maintains riparian habitat. Riparian habitat is also defined as wetlands and is often critical habitat for threatened or endangered species. The majority of the desert riparian/aquatic habitat in Clark County is subject to the Federal Clean Water Act (CWA) and the “no net loss’ policies established for wetland habitats. These apply to wetlands on both Federal and non-Federal lands, including Native American reservation and private lands, and generally require avoidance, minimization, or mitigation of any impacts to this habitat. Preventing loss of wetland habitats often depends upon the water cycle not being impacted by water diversions.
Under the authority of the Endangered Species Act, Clark County initiated a 30-year Multispecies Habitat Conservation Plan with the USFWS starting in 2001[4]. The MSHCP includes 79 covered species in Clark and parts of Lincoln and Nye below the 38th parallel. Signatories (permittees) to the MSHCP include Las Vegas, Henderson, Boulder City, and Mesquite and includes private, municipal, and state lands. The Mojave desert scrub ecosystem provides habitat for 23 Covered Species and 8 High Priority Evaluation Species. There are 13 Covered Species and 5 High Priority Evaluation Species associated with springs within the various habitats in Clark County. Plus, protected native fish in the river: flannelmouth, spinedace, chub, woundfin, speckled dace, desert sucker.
Minimum instream river and spring flows[5], supported by conjunctivity with bank storage and groundwater, could be required on springs and river reaches to protect endangered aquatic species and riparian habitat, limiting VVWD’s “paper” water rights on the river and springs.
From the VVWD Master Plan 2020 “…It should be noted that there is no guarantee that the District will be able to acquire additional groundwater, and if additional groundwater rights can be acquired, it will likely be through a long process. This considered, the District should plan to carry out an aquifer study several years prior to reaching the limits of existing groundwater rights to provide ample time for future source planning”. Thus the Master Plan itself recommends a conjunctive study. VVWD has “paper” water rights for which there may be insufficient “wet” water rights. This and the perennial yield of Basin 222 requires a conjunctive study to determine if there is adequate groundwater to meet “wet” water rights and whether the aquifer is being mined (pumping exceeds recharge) now or in the future.
The Nevada Water Engineer can fund a conjunctive study of a basin once a correlation between the groundwater and surface water has been established. The correlation between Basin 222 and the Virgin River has been established in a doctorial dissertation by J. Asante and Dr. D. Kreamer of UNLV[6]. As stated in the study, based on hydrochemical data, the floodplain aquifer is connected with and interacts highly with the Virgin River. Thus, a correlation between surface water and groundwater has been established, which should lead to the Nevada Water Engineer funding a conjunctive management study.
In addition to a conjunctive study at this time, VVWD should perform habitat surveys and wetland mapping on all their surface water appropriations to determine if they must comply with the Clark County MSHCP and the Federal CWA and limit water diversion to less than their “paper” water right: VVWD has “paper” water rights on the following surface water systems:
Cabin Springs
Mica Notch Springs
Indian Spring
Seep Spring
Dud’s Spring
Nickel Creek
Riverside Virgin River
Halfway Wash Virgin River
Virgin River
In conclusion, we do not know how much water is in Basin 222, we do not know the actual perennial yield from the basin, and we do not know if long-term, greater pumping will “mine” the aquifer over time. Given the 20+-years of drought, climate changes, less snowpack and lower monsoonal precipitation along with extreme summer temperatures, lower spring and river flows, as water demand from development increases, we cannot just “assume” there is and will be plenty of water. The VVWD’s insistence that we have enough water may only be true as long as they are allowed to overdraft the aquifer.
Hard, reliable data is needed for city government to make intelligent decisions. Mesquite cannot assume there is sufficient water to allow growth to the “grow-out” level without data and surety from a conjunctive study, a wetlands study, and an MSHCP study. Until then the city should place a moratorium on building permits and the State must place a hold on further well development.
Endnotes:
[1] Kevin Brown statement at Mesquite City Council meeting in response to presentation on need for a conjunctive study by Dr. Michael McGreer of the Mesquite Water Alliance.
[2] An acre-foot (ac-ft) is a unit of measurement described as 1-foot of water covering an acre of land, or roughly the water needed for three homes for a year.
[3] A conjunctive study measures the interaction of surface and groundwater, 1.e., how the volume of water in the aquifer is recharged from surface water sources (river seepage, precipitation, up-gradient flow, etc.) and how to balance pumping with recharge to not exceed the aquifer’s perennial yield and prevent “mining” of the aquifer.
[4] Clark County Multiple Species Habitat Conservation Plan and Environmental Impact Statement for Issuance of a Permit to Allow Incidental Take of 79 Species in Clark County, Nevada September 2000.
[5] Hill, M.T., W.S. Platts, and R.L. Beschta. 1995. Ecological and geomorphological concepts for instream and out-of-channel flow requirements. in P. Calow and G. E. Petts (eds.). Rivers Handbook: Hydrological and Ecological Principles, Vol. 1. Blackwell Scientific Pub., Cambridge, Mass.
[6] Asante, Joseph, “Evaluating Recharge and Dynamics of Flow in the Lower Virgin River Basin, USA: Interpretation of Hydrochemical and Stable Isotopic Data” (2012). UNLV Theses, Dissertations, Professional Papers, and Capstones. 1533.
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