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Our Watershed- Mother Nature's water system

Editor’s note: This is the fourth in a series running over several consecutive Fridays. It is written by members of the Hermit’s Peak Watershed Alliance, which seeks to foster land stewardship in the Gallinas, Sapello and Tecolote watersheds.

The city of Las Vegas and its residents depend on water in the Gallinas River for more than 90 percent of its municipal needs. Storrie Lake Water Users Association receives almost all its water from the Gallinas River. That’s a serious dependency.

For the past six months, the Gallinas River has been flowing at a quarter of its historically recorded average (USGS gauge) for this time of year. El Porvenir Creek has gone dry multiple years in a row, a sight not seen in the previous two generations. Since 2000, annual flows have been below average all but four years.

Yes, drought conditions play a major role in reduced flows. It is also true that the quality and quantity of water available to Las Vegas and the timing of its delivery is significantly influenced by the condition of the land.

When it is functioning well, the watershed acts as a water reservoir, filtration and piping system. It provides these services free of charge and in perpetuity if its capacity is protected. When it’s not functioning well, it requires numerous interventions and expensive infrastructure like dikes, dams, flood control structures, filtration systems and sediment storage areas.

In a healthy watershed, plant communities coupled with meandering river channels and floodplain, carry water into soils and aquifers for storage and filtration. Plant roots transport water below ground while their above-ground parts slow water movement. The soils are like a sponge. The rivers slowly receive subsurface water and combined with a healthy floodplain, moderate the highs and lows of water delivery throughout the year.

Water quality, chemical and thermal conditions of water are largely regulated by land cover and land use. When land is not covered by plants, the water that crosses that land carries more sediment with it into the river, decreasing water quality. Fertilizers from crops, sewage from homes and barnyards and petroleum products washed in from roads, all flow into the river system. Chemicals, sediments and even trash you see on the side of the road must be removed from the water before it’s safe to drink.

Plants in uplands, along river courses and in wetlands can trap and filter both sediments and chemicals before they reach the river transportation system. This improves the water in your home and reduces the costs of water treatment.

In general, water quality related to chemicals and sediments, is good in the Gallinas River.

This is to the credit of our land stewards and to the limited degree of development in the upper watershed. But sedimentation is a problem at some times of the year, especially during storm events. During these times the city of Las Vegas cannot divert water for storage in our reservoirs.

Water temperature is also higher in the Gallinas Watershed than it should be, reducing water quality. Warm water temperatures, greater than 68 degrees Fahrenheit (20 degrees Celcius), encourage algae growth, which reduces water quality and affects its taste. Warm water cannot support healthy trout populations. The Gallinas River and Porvenir Creek are both considered temperature impaired by the New Mexico Environment Department.

There are several causes of this warm water. Temperature is increased when water flows through areas without shade. Low stream flows and a lack of storage time in cool soils encourage increased water temperature. These conditions all occur in the Gallinas.

It is often thought that plants use up all the water. Actually, plants provide more water to our river recharge than they use and offer many other benefits. Benefits like shade, protection from wind, improved water infiltration, providing organic matter to the soil, erosion control, flood control and food to fuel the entire watershed. The lack of healthy native vegetation is both a cause of a degraded watershed and a symptom of one. The Gallinas is no exception.

The timing of water delivery through our watershed’s river system is related to spring runoff and storm events. However, the high flows tend to be higher and the low flows tend to be lower when soils are compacted, bare or have reduced plant cover and when rivers have been straightened or entrenched (down cut). Healthy uplands and river systems can moderate peak flows and extend higher flows for longer after wet periods, resulting in more consistent water flow that can be withdrawn for our use.

Some level of human infrastructure is needed to supply water to the population of Las Vegas; the watershed alone cannot do all the work. But to the extent that our watershed can function well, it reduces the need for costly water storage and treatment as well as flood prevention and remediation infrastructure. The benefits of a healthy watershed also go well beyond water.

Next week: Conditions and threats to the Gallinas Watershed.

The Hermit’s Peak Watershed Alliance may be reached by visiting its website at hermitspeakwatersheds.org or by calling 505-425-5514.