SIERRA VISTA – In the trial over the U.S. government’s claim of water rights from the San Pedro River, a number of experts in the fields of biology, hydrology and ichthyology on both sides have weighed in on the importance of sustaining the ecosystem of the San Pedro Riparian National Conservation Area (SPRNCA).
The U.S. attorneys claim the amount of water being sought is needed to support stream flows, maintain natural hydrologic processes, conserve resources, protect and enhance the SPRNCA. It includes numerous seeps, springs and ponds within the SPRNCA.
The government says it is only seeking the amount of water needed to sustain the abundance of wildlife, both plant and animal.
One big issue being discussed at trial has been depth to groundwater for vegetation and how much river flow is affected by water use of vegetation, especially the canopies of cottonwood and willow trees. The trees take their water from the baseflow in the riparian area.
U.S. Bureau of Land Management (BLM) studies determined the vegetation needs 12,735 acre feet per year to maintain proper health, as is stated in its third amendment statement of claim. That is but one area where the amount of water needed annually is being determined as part of the overall claim.
The water needs of the trees
The roots of willow and cottonwood galleries need water to be within 5 to 15 feet, respectively, to survive, stated riparian ecologist Mark Dixon, a witness for the U.S. To sustain them, he suggested it’s wise to request a claim allowing a safety margin in depth to groundwater to ensure their health.
Just how long a cottonwood could survive if the level dropped below that point has not been studied, stated Steven Carothers, SWAC aquatic and terrestrial biologist, hired by Freeport Minerals. Though the water level of the baseflow could drop far enough to compromise the trees, a surge of stormwater could bring the water levels back up high enough to restore contact with the roots.
During testimony for the U.S., former BLM SPRNCA manager Bill Childress said the shade the trees provide would reduce evaporation from the river and keep the area near the river cooler, a plus for the fish.
Water needs for the fish
Testimony showed the two remaining native species of fish are the longfin dace and the desert sucker. Of the two, the longfin dace has proven to be an adaptive species with far higher numbers than the desert sucker, according to fish counts done by J.A. Stefferud over a period of decades. The desert sucker had the highest counts in the Charleston area, where the flows remain perennial.
U.S. witness William Miller, fisheries expert and owner of Miller Ecological Consultants, said more water in the river means the native fish have a better opportunity to survive, especially during the summer months when it is dry and hot. The BLM’s proposed plan to add water from the underground aquifer during the months prior to the monsoon would help the fish.
Both sides agreed non-native fish counts done by Stefferud show no one species is gaining a foothold. Also, the non-native fish tend to populate deeper, stiller water, like the ponds created by beaver dams.
Beavers, good or bad
Beavers and their dams were brought into the limelight as both sides, although agreeing on their importance to the ecosystem, discussed their possibly problematic ponding.
The U.S. witnesses expressed their viewpoints in favor of the beaver and their dams. The ponds create habitat for many types of plants and provide the riffling water needed by the longfin dace for reproduction, as well as deeper pools for the desert sucker. The dams can also slow the river and collect sediment.
Witnesses for the defense questioned the logic of promoting dams and ponds since the slower, deeper water provides habitat for non-native fish, which puts the natives at risk. Carothers pointed out the decline of the desert sucker began after beaver were introduced.
However, on cross-examination, Carothers agreed the desert sucker showed decline in years when the beaver were not present.
At the end of three weeks of testimony, both sides provided foundations for their arguments on the water needs of the SPRNCA.
The back and forth of testimony and rebuttal will continue on Monday, Feb. 25, in Maricopa County Superior Court.
Witnesses to come
For the U.S. government, avian ecologist Leslie Brand will provide relevant context regarding the regional importance of the SPRNCA from her experiences.
Hydrologist Dave Romero will explain the reason for the requested water rights claim and will try to show groundwater pumping has captured groundwater that would be otherwise available to the river and the riparian area.
David Goodrich, U.S. Department of Agriculture research hydrologic engineer, will discuss water issues within the San Pedro River basin.
Justin Huntington, research professor at the Desert Research Institute, will explain his conclusion that there has been no statistically significant change in the amount of vegetation since the SPRNCA’s establishment.
For the defense
Rich Burtell, Plateau Resources.
Rick Coffman, vice president of Castle & Cooke.
Chuck Potucek, Sierra Vista city manager.
Pat Call, Cochise County Supervisor.
Andrew Smallhouse, rancher.
No information provided: Matt Lindburg, Jeff Weaver, Ann Redmond, Theresa Murphy, John Bodenchuk, and Lincoln Dahl.