George Sibley: Down on the Ground with Groundwater

Water again. Just can’t get away from the stuff – literally can’t, I guess, being myself about 70 percent just water that learned how to stand up and look around.

What’s caught my attention this month is a new study from the U.S. Geological Survey, finding that more of the water in the Upper Colorado River streams and rivers originates from groundwater than from snowmelt runoff. This is a little counterintuitive – especially now in May and June, with our rivers so exuberant – sometimes a little ominously – with snowmelt.

We know a lot about – and love – our streams, rivers, lakes and other “surface waters.” But groundwater – the water that sinks into the ground, moving through the tiny pores in both soil and rock – is out of sight and mostly out of mind. It’s still the big spring flows that lead us to equate the health of our water supply with the snowpack and its water content – a big snowpack means a big runoff and a good water year. Except when it doesn’t, like this year. The snowpack is close to the 30-year average, but the runoff from that snowpack is forecast to be less than 80 percent of the average (as of mid-May).

Assuming such mysteries to be related to the unseen groundwater, the USGS developed techniques for determining the portion of water in a stream that has percolated through the ground on its way to becoming part of the surface waters. They conclude that, overall, three-fifths of the water that flows into Lake Powell (ultimate destination for all Upper Colorado River tributaries) came into the streams as groundwater. In the higher headwaters streams of Central Colorado, the ratio varies more dramatically. Groundwater content in the high streams varies from as little as 13 percent to as much as 80 percent of the stream flow, depending on the overall water-year precipitation (October through September), stream geography, and when the snow becomes water and how fast. The USGS study covered only the Upper Colorado River tributaries, but similar situations probably prevail in the other mountain rivers originating in Central Colorado.

But wait a minute, you might say: isn’t the groundwater also mostly from melting snow? Yes, of course – but it’s snowmelt that sank in rather than running off. And that’s a distinction with a real difference.

Most of us indiscriminately and unquestioningly love our “surface waters” – for their diverse kinds of beauty, for the adventures they afford, for the riparian communities that shade them and us, for the community of aquatic life they carry, for their imprint on the land which so resembles our own circulatory systems.

But their aesthetic qualities shouldn’t obscure the fact that the streams and rivers in a watershed are truly “running off” – they are water being “shed” by the watershed, water that’s not staying around to nurture life. And in the next valley it goes to, if left alone, it will nurture no life there either beyond the narrow riparian strip beside the river and maybe a temporary spring flood into its floodplain. And so it will go, collecting other “shed water” as it passes through until it dumps all that freshwater back into the salty sink of the ocean.

Rivers, in other words, don’t water the land; they drain it, if left to follow their nature. We – humans, beavers and some kinds of plants – do what we can to slow or stop that natural act: we create dams and other obstacles that hold back the runoff of precious freshwater; we spread the water out on the land again to give it another shot at sinking in to nurture plant and animal life.

Through the 20th century, our main focus in water development was the storage and distribution of surface waters. Now, as we are preparing for a future in which we anticipate continued population growth in the Colorado River Basin, with climate changes diminishing overall water supply, we hear calls for more surface-water storage. The Colorado Water Plan alone calls for an additional 400,000 acre-feet of surface storage by mid-century, mostly on the Front Range.

But we have few remaining passable dam sites – and realistically, we have just about stressed the surface water supply to the max in most of our western river basins. The reservoirs we already have aren’t always full. There’s also the fact that surface water stored on the surface pays a heavy tax to the sun through evaporation. Roughly a seventh of the Colorado River’s total flow is lost to evaporation – better than losing most of the river in an uncontrolled spring flood, as used to be the case, but still a significant loss.

So is it maybe time to shift our focus from surface water to groundwater – and to the potentially useful interactions between surface and groundwater? Last year I wrote in this column about the really modest amount of freshwater on the planet and where it is found (CC No. 255, Sept. 2015). At any given time, according to the USGS, only around 2.5 percent of earth’s water is fresh enough to support land-based life – and more than two-thirds of that is “frozen assets” (glaciers and ice sheets). Nearly all of the remaining third is groundwater, while less than one percent is surface water (rivers, lakes, marshes) – about 9/10,000ths of the planet’s total waters. All of earth’s rivers drain off to the oceans a modest 2/10,000ths of earth’s total waters.

Given those numbers, it seems behooving to stop focusing on stretching the rivers to cover the supply gap and start working with the groundwater that makes up as much as 80/10,000ths of the planet’s water.

There are two types of fresh groundwater; most useful is tributary groundwater, which lies close to the surface and interacts with the surface streams as well as plants at the surface. Globally, there is roughly eight times more tributary groundwater than water in streams and rivers.

The other type is non-tributary groundwater which lies deeper in the earth, a lot of it in layers of porous stone; it has no direct interaction with surface water or tributary groundwater – unless it is pumped up from the depths – which we do increasingly. Globally there is around 60 times more non-tributary groundwater than tributary – maybe 500 times more water than is in all the world’s rivers.

So what could, what should we be doing? We are in fact already doing a lot of it, or learning how to do a lot of it, but a lot of it needs to be done in a more coordinated, intensive and extensive way. In the high headwaters of the Upper Gunnison, The Nature Conservancy is pioneering work in the restoration of once wet meadows that have been gullied, either by natural “gullywashers” or by human grazing errors, or both. A gully lowers the water table in a meadow, reducing the amount of water available for the wet-meadow plant community; grasses diminish and sagebrush takes over – a dryland transformation that changes animal populations, too.

But another change is water rushing down the gullies, deepening them, rather than soaking into the grassy ground. Small rock structures – many hand-built – can reverse that process, stop the erosion, restore a high water table and the slow seep of groundwater rather than the rush down the gully. Some larger gullies require larger equipment and a different kind of structure, but the goals are the same: slow the flow of the water, maintain a high water table. There is no shortage of high-country gullies to tackle.

Farther downstream, stream restoration combined with more efficient agricultural irrigation could (with minor changes in water law) both improve the height of the water table and the health of the streams with minimal need for additional streamflow. This requires collaborations between ranchers/farmers and environmentalists and recreationalists – not easy alliances to build – and it will require substantial funding that is hard to find in America today where we mostly seems to want to “live free” (from responsibility).

The cities can do a lot in a couple ways. Cities that have been “mining” a lot of non-tributary groundwater are experimenting with recharging the non-tributary aquifers in years with above-average surface water. This remains something of an experimental process, with no certainty how much of the water pumped down will be available for pumping up again, or what the quality of it will be.

There is also a lot of experimentation in cities to better utilize the water resource formerly known as “stormwater” to be gotten rid of as quickly as possible. Los Angeles water leaders believe they can eventually supply all of the city’s water needs if they can capture and hold in the ground all of the precipitation they formerly piped and channeled off to the ocean

We are going to have to become much better organized as communities and regions if we are going to meet the future challenge of water supply. But it will be a lot easier if we can get beyond the belief that it all has to come from stretching the surface waters to do more, and can apply our imagination and resources to developing – and conserving – the more abundant groundwater.

George Sibley is both watered and grounded in Gunnison.