Category Archives: Science

Groundwater pumping reduces river flows

Water allocations over done.

In Nevada, as in many other western states, those who first put water to beneficial use (growing a crop or providing drinking water to a town, for example) have a right to use that water over those who come later. Early on most water used in the state came from surface waters such as the Truckee or Humboldt Rivers or smaller streams which flowed from the state’s numerous mountain ranges or from local or large regional springs. Most of the surface waters in Nevada were already claimed before the 1930s. The beneficial uses claimed became water rights. Water rights can be bought and sold.

Native Americans were already here.

Sketch of the Pyramid from Fremont's Report on surveys in Nevada and California (1844)
Sketch of the Pyramid from Fremont’s Report on surveys in Nevada and California (1844)

Ignored in the claiming of water rights beginning in the late 1850s was the cyclic nature of water availability in the dry Great Basin and Mojave Deserts. Water that is present in a sagebrush covered valley one year may be absent the next one or longer. And while the newcomers claimed the water for themselves, none appeared to notice that the Paiute, Shoshone, and Washoe Peoples already occupied the land and were prior users of the rivers and springs that nourished many wetlands, lakes, and meadows with the wildlife and plants the People depended on for survival. The Indigenous population found that the water that supported their way-of-life for thousands of years was used somewhere else by someone else. The water supplied by the natural world that had sustained them disappeared.

Newcomers claim the water.

Native American Petroglyph

Over the decades more and more water claims depleted rivers, lakes, springs, and wetlands throughout the state. Lakes such as Pyramid fed by the Truckee River and Walker fed by its namesake shrank as their river’s flows diminished – or disappeared altogether. And large wetlands on the Humboldt and Carson Rivers shrank as water went to farms and industry.

Demands on the Truckee River exceed the rivers ability to keep up. The river is particularly stressed during droughts which could become more common.
Long stretches of dry winters result in only a trickle in the Truckee River through Reno. Water rights diversion remove most of the small flow that remains.

Taking water flowing in a river, stream, or spring has an immediate effect. For example, consider a small stream that has a flow of 10 cubic-feet per second (CFS) with two users who each claim 5 CFS. If water user number 1 diverts half of the flow of the stream to an irrigation ditch, then the flow downstream of the diversion is immediately reduced to 5 CFS. The remaining water in the stream continues downstream to water user number 2. When water user number 2 diverts his share, then downstream of the diversion, the stream is dry. In a different year or later in the season, when the stream’s flow is 5 CFS, then water user number 1 diverts all flow and nothing remains for water user number 2. When the stream has 1 CFS, water user number 1 still diverts all the flow, but is unable to get her full water right and water user number 2 again has no water to divert.†† From the environmental perspective, the stream no longer has flow to support riparian trees or meadows below the diversions and eventually, they disappear. Essentially, every year becomes a drought year downstream of the diversion.

1.0 cubic-foot per second is approximately 7.481gallons per second. Early miners were among the first to appropriate water in Nevada using “miner’s inch“. Today, Nevada has a legal definition that a “miner’s inch” is equal to 0.025 cubic-feet per second.
†† Certain surface water allocations depend on “return flow” when not all the water is consumed irrigating a crop or water is returned to a stream from a sewage treatment facility. “Return flow” can then be diverted by another appropriator.

Water already claimed in rivers and springs.

The appropriation of surface water had negative effects on the rivers and streams and springs, because the original benefits of flow through the river’s environment were reduced. But the cyclic nature of water in the desert continued and when rivers and springs couldn’t keep up with the water users demand and reservoirs shrank, a new group of folks wanted water that they could depend on whether it rained or not. Groundwater pumping was a promise of unlimited supply – that unseen resource just beneath your feet. The promise was a false one and today we face a reckoning of over spending our water bank account on both fronts.

The “new” water: Groundwater.

(Illustration: USGS)
Pumping from an aquifer can draw water from nearby streams and lakes. (Illustration: USGS)

Pumping significant amounts of groundwater from aquifers was really not possible during the time when most of the state’s surface water was allocated between the various industrial and agricultural users. Beginning in the mid-20th century, however, groundwater extraction with powerful pumps became more and more common. The Nevada State Engineer (NSE) allowed groundwater wells to be drilled for agriculture or other uses even in basins with fully appropriated rivers and streams and springs such as the Humboldt River and the Walker River and around Moapa’s springs. The NSE now admits, in many cases, the overallocation was known at the time, but the NSE didn’t expect that the people getting the permits would be economically successful (an erroneous assumption as it turned out!) or that they didn’t consider the negative effect groundwater pumping would have on rivers and springs. The damage to rivers and springs due to over pumping, however, is a matter of hydrology. The excuses for why it was allowed to continue for decades doesn’t change the negative outcome for river and spring flows and the consequences for the people dependent on them and to the fish and wildlife that can’t survive without them.

Pumping from two wells extends the cones of depression.
Pumping from two wells quickens the drawdown of groundwater. Many of Nevada’s desert valleys have dozens of approved pumping wells. In too many cases, there are also surface water users dependent on flows from rivers or streams or springs now seeing affects due to groundwater drawdown. (USGS Illustration)

In all groundwater pumping, groundwater levels decline by the very action of extracting water and bringing it to the surface. Essentially, a cone-shaped hole develops around the well. If pumping ceases soon after the pumping begins, the cone-shaped hole or depression slowly fills in and after a long enough period of time, it may get close to the original groundwater level, but that generally takes far longer to happen than the length of time the groundwater pumping occurred.

Over appropriating the groundwater.

Overallocated basins shown in green, yellow, and red. Note: “PY” is perennial yield, an estimate of the amount of water consumed by plants and surface water discharges (springs, creeks, and rivers) before the proposed development of groundwater.[ NSE office graphic]

Over the decades the Nevada State Engineer (NSE) has permitted groundwater users to over-appropriate as many as half of Nevada’s hydrographic basins in the state with the least amount of water. Theoretically, pumping is supposed to be “balanced” by drying out the surface and eliminating plants and water “discharges” (like springs) that use groundwater through evapotranspiration. (Eliminating all evapotranspiration to achieve this “balance” with groundwater pumping can result in a barren landscape increasing dust as well as damaging seeps, springs, and meadows dependent on groundwater.)

Pumping groundwater appears, at first, to be benign. When groundwater pumping begins, it removes water that may be a source of supply to rivers or springs, but the effect of pumping takes time to deplete the flow of a river or spring (see illustration above). The further away the river or spring is from the pumping, the longer it takes. Effects of the State’s overallocation of groundwater and the near complete allocation of surface water are now being felt with continually declining groundwater levels in as many as 50% of Nevada’s basins, but it is also affecting iconic rivers like the Humboldt – the largest river completely contained within the state’s borders. However, no river or stream is immune to the damage caused from pumping of groundwater (or the over allocation of surface water, for that matter). The extent of the pumping, leading to over pumping and continually dropping groundwater levels, harms the environment and leads to conflicts between water rights holders and to discord between and among rural and urban Nevadans.

Nevada water law is clear.

Before approving any water applications, Nevada water law (Title 48, NV Revised Statutes) requires the NSE to find that water is available at the source and it will not conflict with existing water rights. This requirement applies to both the allocation of surface water or groundwater. Nevertheless, the NSE has, in fact, allocated water far beyond the available supply. In the graphic above, those areas shown in “red” are 300% or greater over the available supply and the “yellow” and “green” areas are more than 200% or more than 110% over the available supply, respectively. It is easy to see why conflicts are escalating between and among users and why the environment in many areas suffers from a lack of water.

Nevada State Engineer now wants changes to the law.

The NSE now wants the legislature to change the law to allow the NSE to “deal with” the conflicts his water office has created over many decades (and in contradiction to the law’s provisions.) These changes are embodied in two pieces of legislation the NSE has brought to the 2019 Nevada Legislature – AB30 and AB51. Check out our next blog to see how these could affect our critically important rivers and streams and springs throughout Nevada.

Derby Dam (1905) diverts Truckee River Water away from Pyramid Lake. The project was the first of the new Bureau of Reclamation which was created by the Federal Government. The project still operates today and has shrunk Pyramid Lake by 80 feet and dried up Winnemucca Lake. (Historic photograph of the project’s completion: UNR Library Collection)

Snow drought in an average year of precipitation for Truckee River

NRCS 4-24-2018 - Total Precipitation vs. Snow Water Equivalent for water year to date

The Truckee River watershed saw more rain than snow this year. So, this year appears to continue the trend of at least the last decade as rain replaces snow – especially at lower elevations. The maps show just how significant the effect is as we approach the end of the first month of spring. Many sites in the Truckee River basin (including the Tahoe basin) are reporting 101% of the longterm average for precipitation. The picture is different for snow water equivalent, however. Snow water equivalent (the amount of water in the snow pack) is almost or well below the longterm average for this date for sites at lower elevations. You have to go to the highest elevation sites to see average snow water equivalent conditions.

In the graphic below, the blue dots on the left represent sites where total precipitation is 101% and the white sites represent 100% of the long-term average. On the right the 3 sites (between 6400′-7700′) in red have 0% of snow water left; the orange sites have 50% of snow water left compared to the long-term average. Only the site at Big Meadow (8235′) shows 101% of snow water left and one site at Heavenly Valley (8500′) shows 100% of snow water left – both high elevation sites. Click on the graphic to see full size. Or check out the site yourself here.

NRCS 4-24-2018 - Total Precipitation vs. Snow Water Equivalent for water year to date

NRCS 4-24-2018 – Total Precipitation vs. Snow Water Equivalent for water year to date

If the trend continues as expected, there will be very little snow left to melt in the late spring and early summer. When snow disappears earlier, natural stream flow of tributaries and the Truckee River itself decrease. Less natural stream flow often results in additional releases from reservoirs or increased ground water pumping because of our long, dry summers.  Ultimately, it will negatively affect recreation and fish and wildlife that depend on water in the Truckee River.

“The Disappearing West”: NV ranks high in degraded rivers

“The Disappearing West”, a report produced by Conservation Science Partners based in nearby Truckee, documents the dramatic degradation of rivers in an interactive series of maps and animated illustrations. The report appears online at the Center for American Progress website.

Truckee River in downtown Reno trickles under the Virginia Street Bridge in late 2014.

A concrete walled Truckee River trickles through downtown Reno in late 2014.

The report attempts to map 300,000 miles of rivers and streams in the 11 western states and show the human impacts made to their flows and floodplains. The interactive map allows anyone to zoom in on any western state location and identify the extent of damage to large rivers and small rivers and headwater streams in mountain ranges from the Rockies across the Great Basin to the Sierra and Cascades. The map colors range from deep blue to fire red depicting a range from near natural condition to extremely altered or unnatural condition for either stream flow restriction or floodplain modification. Some states have far more severely modified streams and rivers than others. Overall, however, the west appears more red-colored than blue-colored with surprisingly small streams high in mountains suffering from flow reduction and floodplain modification. While the report offers a valuable tool to look at how our rivers and streams are suffering, we’ve discovered that reporting on the Truckee River flows below Reno-Sparks underestimates the severe dewatering of the river at Derby Dam.

A cautionary note: It could be that the report underestimates damage from flow reductions in other states if the Truckee River flow diversions were missed.

The report shows Nevada ranked 2nd in the major rivers and 3rd in the smaller rivers categories that suffer from flow restrictions, 94% and 31% respectively. Utah ranks first in reduced flows in major rivers at 96%. I used the “Disappearing Rivers” information to develop the bar graphs, presented below, ranking states by flow restrictions and floodplain alterations for major rivers.

Ranking of flow restrictions for major rivers by state

Ranking of flow restrictions for major rivers by state (based on information in “Disappearing Rivers” Report-DLG)

Ranking of floodplain alteration for major rivers by state (based on information in “Disappearing Rivers” Report-DLG)

Likewise, the report also shows Nevada 2nd in modification to major river floodplains at 73% and smaller river floodplains at 51%. Colorado ranks first in major river floodplain modification at 77%.

Reducing river flows and developing river floodplains can eventually kill riverine ecosystems by eliminating the riparian forest that grows along the stream, warming the stream from reduced flows, eliminating cold water fish and invertebrates that live in the stream as well as increasing pollution and reducing recreation.

The report separates the rivers and streams into categories: headwater streams with less than 6 cubic-feet-per-second (CFS), smaller rivers and streams between 6 CFS and 163 CFS, and major rivers with more than 163 CFS.² In Nevada, the Truckee, Carson, and Walker Rivers that originate in California’s Sierra Nevada all had historical average flows greater than 163 CFS. The Humboldt River which is entirely within Nevada also had historical average flows greater than 163 CFS. Today, the Truckee River is a mere trickle at Pyramid Lake when US Bureau of Reclamation diversions at Derby Dam take as much as three-fourths of its flow to farms in Lahontan Valley; the Carson River is essentially dry during many summer and autumn seasons before it reaches Lahontan Reservoir due to upstream diversions; and the Walker is often completely dry – sometimes for years – before it reaches Walker Lake. The Humboldt River, likewise, is more frequently dried out before it reaches Rye Patch Reservoir upstream of Lovelock.

Any measure of flowing water can take a little getting used to, but remember, the flow in a river or stream is measured by how much water (volume) is moving downstream over a period of time. It can be in gallons-per-minute or cubic-feet-per-second or acre-feet per year. The US standard way to measure flowing water in a river is CFS or cubic-feet-per-second.¹

Lower Truckee River flow restriction much worse than shown in “Disappearing Rivers” Interactive Map

The Disappearing Rivers analysis shows the lower portion of the Truckee River as having only 8% flow restriction in the lower River between Derby Dam and Pyramid Lake. Unfortunately, this is not accurate. The screen capture from the interactive tool shows the diversion at Derby Dam, but inaccurately says it is only 2,500 acre-feet. It isn’t clear where that number comes from.

Disappearing Rivers: screen capture of river tool's depiction of flow restriction of the Truckee River below Derby Dam is incorrect.

Disappearing Rivers: screen capture of river tool’s depiction of flow restriction of the Truckee River below Derby Dam is incorrect.

In fact, tens of thousands of acre-feet of water are diverted from the Truckee River most years and hundreds of thousands have been diverted in the 21st century alone. So, the representation in the online tool for the Truckee River flow restriction downstream of Derby Dam³ isn’t correct. The problem appears to be that the data used to model the restricted flow caused by Derby Dam doesn’t accurately reflect how much water is diverted on average over an entire year. Derby Dam itself, doesn’t store much water, but the effect of its diversion is the most significant loss on the entire Truckee River below Lake Tahoe.

Example display from the Disappearing Rivers Project interactive map (click for full sized example)

Example display from the Disappearing Rivers Project interactive map

Despite the problem I’ve identified where the Disappearing Rivers Map underestimates restricted flows for the lower Truckee River below Derby Dam, the tool remains valuable to show how our rivers have suffered from loss of flows and modification to the floodplains in Nevada and throughout the 11 western states. The tool affords even the casual user a stark window into the damage inflicted on our rivers from continually taking too much floodplain land for development and too much water from river flow.

In broad terms, the summary provided for the state of Nevada is sobering:

“In Nevada, 53 percent of all rivers are altered. That’s equal to 3,593 unnatural river miles— enough to cross the state more than 11 times. Of the 11 Western states in the Disappearing Rivers analysis, Nevada had the 5th most altered rivers in the West. When broken down by size, 96 percent of all major rivers, 64 percent of all smaller streams and rivers, and 36 percent of all headwaters are altered.”

How can we reverse continual losses of river flows and floodplain lands? Can society embrace increasing natural river flows and restoration of floodplain lands? Increasing population and climate change is making the job of fixing what ails our rivers harder. This report makes clear that in a little over a century, we’ve diverted at least 61% of the flow of our western rivers and negatively modified 63% of river floodplains. And, additional impacts to river flows and floodplains occur daily from the direct effect of development but also from climate change which is making the west warmer – and possibly drier as well. Few people want to have a dry Truckee River surrounded by parking lots and warehouses, but our representatives in federal, state and local governments seem to be taking us to just such a future. It is time to ask politicians to find ways to reduce the amount of water we take from our rivers and aquifers, protect our remaining floodplains, and restore our overdeveloped floodplains.

Restored oxbow of the Truckee River at the Nature Conservancy's McCarran Ranch.

Restored oxbow of the Truckee River at the Nature Conservancy’s McCarran Ranch.

There have been some restoration successes on the Truckee River over the past couple of decades. We have seen the restoration of several floodplain reaches of the Truckee River below Reno from Lockwood to the McCarran Ranch. The Nature Conservancy’s McCarran Ranch represents one of the earliest successful efforts to show how a degraded river can be transformed with a vibrant riparian corridor of wetlands and forest that can support spawning trout and a valuable recreational fishery and recreation. The Truckee River Water Quality Agreement between the Cities of Reno and Sparks and the Pyramid lake Tribe called for the cities to purchase water rights for the Truckee River to increase river flows during low flow. The Cities have purchased more than 11,000 acre-feet of water which can mean the difference between having a dry river and a wet one. The water purchased stays in the river all the way to Pyramid Lake.

Flows in the Truckee River can be greatly improved by reducing diversions from the river, improving farm practices, and increasing water conservation in cities and towns along the river.

Now is the time to make sure our rivers will not continue to disappear.


¹   [For people who like to think in gallons, there are 7.48 gallons in a cubic foot. For example, during February 2018, the Truckee River has been running between 350 and 450 CFS through downtown Reno or between 2,618  and 3,366 gallons per second.  You can check out the flow of the Truckee River every day in the RGJ newspaper on the weather page or look on the TROA website under daily report] 

²   6 CFS for one year is 11.9 acre-feet or 3.88 million gallons; 163 CFS over a year is 188 thousand acre-feet or 38.5 billion gallons. To offset the effect of evaporation from Lake Tahoe requires about 350,000 acre-feet of water each year above what flows out into the Truckee River; likewise, it takes more than 400,000 acre-feet of water each year to maintain Pyramid Lake’s water level.

³    Derby Dam on the Truckee River is the largest diversion on the Truckee River. The dam, completed in 1905, was the first project of the US Bureau of Reclamation called the Newlands Reclamation Project. While most people in Reno and Sparks have never heard of the project, it is responsible for the greatly reduced flows of the lower Truckee River downstream of the cities. The dam allows Truckee River water to be put into a 112 year-old canal, permanently removed from the Truckee River basin, and sent to farms on the lower Carson River’s Lahontan Valley. Once diversions began, Pyramid Lake and the lower Truckee River were sent into a steep decline. Flows in the Pyramid Lake Paiute Tribe Reservation‘s portion of the Truckee River were reduced to just a trickle. Any time during many years (flood years being the exception), a substantial portion of the water in the Truckee River as it flows through Reno-Sparks will end up in Lahontan Valley and not Pyramid Lake due to the diversions at Derby Dam. The dam at Lake Tahoe is also part of the Newlands Reclamation Project and the water stored in Lake Tahoe by the dam benefits farmers in Lahontan Valley. The Lake Tahoe dam can store over 700,000 acre-feet of water by raising Tahoe’s water elevation by up to 6.1 feet.

Derby Dam on the Truckee River diverts water to Lahontan Valley

US Bureau of Reclamation’s Derby Dam on the Truckee River diverts water to Lahontan Valley

Lake Tahoe Dam at the outlet to the Truckee River February 2015

US Bureau of Reclamation’s Lake Tahoe Dam at the outlet to the Truckee River