Part 2 – Upstream: Stabilizing the Rincon Watershed: The Need for Rehabilitation

Posted by Karen Ray on October 20, 2020 5:08 PM

The Rincon Arroyo Watershed regularly feeds excessive sand and silt into the Sandy Draw beast. A previous article looked at the downstream effects of tons of eroded silt and sand migrating off the watershed and washing down, adversely affecting the Rio Grande channel downstream as well as irrigation systems, agricultural operations and communities.

Earlier this year, after touring downstream sites impacted by all the silt movement, a group consisting of members of the South Central New Mexico Stormwater Management Coalition (SCNMSMC, AKA Stormwater Coalition), local agricultural producers and numerous other agencies drove up into the watershed to evaluate the source of the problem.

The group’s goal is to strategize solutions and methods for rehabilitating the watershed that will also inform restoring watersheds throughout the Hatch and Mesilla Valley region. To do so, they have looked for funding opportunities to accomplish the needed work. Initial priority restoration areas have been identified across the 134 square miles of the Rincon Arroyo Watershed, the largest sediment contributor to the fertile Hatch and Mesilla Valleys.

Connie Maxwell, graduate research assistant with the New Mexico Water Resources Research Institute (NM WRRI) and co-chair of the Stormwater Coalition Watershed Restoration Working Group, organized the tour along with Dona Ana County Flood Commission Director and chair of the Stormwater Coalition, John Gwynne, Elephant Butte Irrigation District (EBID) District Engineer Zack Libbin, who  also serves as the co-chair of the Stormwater Coalition, and the leaders of the Bureau of Land Management’s (BLM) local Resource Advisory Council (RAC). BLM Supervisory Natural Resources Specialist Jack Barnitz led tour members across the watershed to observe other examples of severe erosion and channel entrenchment.

At the Point of Rocks Vista in the Jornada Del Muerto, a distinctive rock outcrop that, according to the historic marker, was a landmark for travelers on the El Camino Real, indicating “water was only 10 miles away,” the group had a bird’s eye view of the massive Rincon Arroyo. The ridge overlooks the low mountains of the Little Caballos, draining high stormwater flows down into the watershed and subsequently into the Hatch and Mesilla Valleys, the groundwater basins, and the Rio Grande. The runoff carries a tremendous amount of sediment, causing silting and erosion problems downstream.

The arroyo in this location is bounded by man-made dikes, diversions and low-profile rock structures called bunds or contour stone lines, some dating from the late 50s. These were strategically placed to reduce sediment movement down into the arroyo system and encourage improved vegetation, which aids  in slowing the water and allowing it to infiltrate back into the aquifer. Critical work needs to be done on these historic structures to restore their functionality.

EBID and the Dona Ana County Flood Commission have worked with BLM and private landholders to install rain gauges across the watersheds to aid in understanding what’s occurring with weather events 20-30 miles away. They plan on installing more to help them in their quest to improve watershed health. Esslinger says, “Once we know what’s coming into the valley, we have a better chance to manage it.”

With the NM WRRI, Maxwell has been studying how the condition of the Rincon Arroyo and other arid watersheds effect the energy of the flood flows with a goal of seeking potential watershed restoration strategies. In a 2019 research publication, Maxwell et al. explained, “Throughout the increasingly arid Hatch and Mesilla Valleys, as is common across the Southwest, vegetation loss in upland watersheds is leading to floods that scour soils and transport sediment.” This results in downstream silting in of riparian areas and agricultural infrastructure like flood control dams, canals and ditches as well as the Rio Grande channel itself.  She notes that “higher flow energies and decreased infiltration are diminishing water storage across the landscape, negatively impacting agriculture and ecosystems”. It is vital that the root causes of these high energy flows be addressed rather than the many years of emergency but ultimately bandaid approaches, Maxwell and others at the Stormwater Coalition point out.

The Coalition is exploring a variety of ways to prevent and repair the damage-causing hydrologic energy, including slowing down flood flows, reducing the flow energy, increasing infiltration and promoting revegetation. The basic approach seeks to reconnect the floodplains and spread the flow of stormwater to help correct and rehabilitate the watershed. These methods work together to increase watershed health, control sediment, prevent flooding and recharge the valley aquifers with detained stormwater.

A thorough analysis of the watershed over the last several years has yielded data on flood flows, groundwater infiltration, sedimentation, and erosion rates. The study considered variables such as flood flow connectivity, topographic attributes, surface flow frequency and the makeup of valley bottoms receiving runoff. Researchers also analyzed soil composition, mapped ecological sites and studied both total and average precipitation from 2008-2013.

In these studies, Maxwell and other researchers have a goal to develop new collaborative tools to support land managers across the region. They have studied how flood flow can connect to floodplains across the landscape to replenish soil moisture and reducing flood energy, creating zones that buffer against drought and flooding. They developed a tool that uses landscape and runoff measurements by EBID from 36 storm events over a six year time period to measure the flood dynamics and quantify the most efficient efforts to increase infiltration and reduce flow energy. (Maxwell, Connie M., Alexander Fernald, Dan Cadol, Akasha Faist and J. Philip King. (In press) 2020. Managing flood flow connectivity to landscapes to build buffering capacity to disturbances: an ecohydrologic modeling framework for drylands. Journal of Environmental Management).

At the NM WRRI, Maxwell and other researchers secured a grant through the New Mexico Environment Department to implement watershed restoration measures in two subbasins of Rincon Arroyo watershed to slow flow, capture sediment, and support vegetation. Contour stone lines, wire or brush weirs, one-rock dams, and other low profile rock and debris will be placed upstream from drainage areas to stabilize grades and increase the spreading behavior of runoff. Each of these techniques serves to increase vegetation, allowing for improved infiltration into uplands soils and eventually to the aquifer as the flow is slowed.

Maxwell and Richard Davidson are also co-founders of the Alamosa Land Institute, a non-profit organization, where they have studied and detailed these practices, and additionally mapped out several potential sites for passive retention ponds, just one of several proposed watershed restoration methods. These small, gravity fed ponds are placed out of the main flow area in a floodplain and work to reduce/remove energy from the flow, trapping sediment, which can then be periodically removed. This reduces the quantity of sediment reaching the river and contributing further to ongoing maintenance issues. Keeping the river channel and irrigation system clear and functioning in their roles of water delivery and flood control is a primary goal.

Included in the rehabilitation plan are many miles of roads, over 119 miles of which currently lie at up to two feet below the grade, according to Bureau of Land Management (BLM) maps, leaving stormwater with no way out. NRCS utilizes a variety of methods to restore these sub-grade roadways, provide drainage and harvest stormwater. Part of the NMED project will bring a road restoration specialist to collaborate with the county and BLM in a workshop to establish maintenance protocols that prevent roads from exacerbating erosion.

These proposed measures to repair the Rincon watershed each have their place and purpose, born out by thorough evaluation. However, this is only the beginning. Numerous agencies have awarded funding to aid in developing solutions to this issue. One program receiving an NRCS grant is the Rincon Arroyo Watershed Stabilization Project. This will allow Doña Ana County and its Flood Commission to begin the first Planning/NEPA phase of a Watershed Protection and Flood Prevention Operations Program for the Rincon Arroyo Watershed. Partners to the project include the NMWRRI, BLM, EBID, and the Caballo Soil and Water Conservation District. This phase aims to create a watershed plan to address the root cause of flooding – vegetation loss in the uplands that scour soils and transport sediment. This in turn clogs downstream riparian areas and over 19 miles of agricultural infrastructure as well as overwhelming downstream flood control infrastructure.

EBID has calculated an estimated 32,130 acres of direct effect of watershed health improvements, along with 19.5 miles of canals and drains. The potential positive impact of work done here has far reaching consequences.

Just as important to implementation is ongoing monitoring. An estimated 36.2 acre-feet per year (AFY) of sediment is deposited into the Rio Grande. The system is not static and maintenance must be built in to adjust where needed as well as to empty sediment retention structures, repair erosion caused by larger storm events and continually look for ways to further improve the watershed. The anticipated results promise to be well worth the effort proposed by the collaborative agencies. The time to act is now.

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(EBID Staff Report)