ALBUQUERQUE, N.M., -- What if you could make something good happen, and do so cost-effectively, sustainably and on a grand scale? You’d leap at the chance, wouldn’t you?
Engineering with Nature (EWN) can make this happen. EWN is a holistic approach for planning, designing, constructing, and operating engineering projects that relies on natural forces and processes to help create and maintain the projects. The end result is a sustainable, resilient, long-term solution to ecosystem restoration, navigation, and other problems. EWN is not a novel concept, but has become an increasingly important strategy for redressing ecosystem damage over large landscapes.
The Middle Rio Grande in Albuquerque is one such damaged landscape. The remaining floodplain in this 41 mile-long reach looked like a “war zone,” littered with jetty jacks and abandoned construction rubble. Invasive species dominated the understory. Gone was the riparian gallery forest mosaic (bosque), with its park-like vistas interspersed with grassy meadows and wetlands. Gone was the wide, braided river with it spring overbanking floods. The change was profound, transformative. What was lost through dredging, levee-building, and dams couldn’t be restored in a day or a year. The scale is too vast, the cost too high.
EWN offered a cost-effective and sustainable way for USACE Albuquerque District Planner Alicia Austin Johnson and Ecologist Ondrea Hummel to restore portions of this floodplain. EWN features were established under three projects:
- The BioPark Section 1135 project restored nine acres of wetland and 48 acres of bosque.
- The Rt. 66 Section 1135 project restored 121 acres of bosque.
- The Middle Rio Grande Restoration Section 3118 project restored 916 acres of habitat in 18 areas along a 26-mile stretch of the river.
Central to their EWN strategy has been to reintroduce spring floodwaters to the floodplain to re-create a hydrologic environment more favorable to the establishment of native willow and cottonwood. “This creates a ‘home-court advantage’ for native species,” Austin Johnson says.
Bringing floodwater into the bosque means bringing the land down to water level through bank terracing, construction of high-flow channels and backwater channels, and connecting unused irrigation ditches to the river. As the spring flood rises, it spills into these features, saturating the ground, recharging the near-surface water table, and creating slackwater nursery habitat for the endangered Rio Grande silvery minnow. As floodwaters recede, young-of-year minnow migrate to the main channel, and the roots of native willow and cottonwood seedlings track the summer water table decline.
Austin Johnson is pleased with this outcome: “Although we focused on a multi-species approach to the restoration, we expect the year-on-year success of these channels in creating minnow nursery habitat to be phenomenal.”
Away from the river, the land was lowered to the water table by creating depressions that intersected the spring water table. Willows established in these “swales” are maintained indefinitely by seasonal water table fluctuations. “Within a year of establishing our first swale, the willows were attracting endangered Southwestern willow flycatchers,” Austin Johnson observed. “We hope in the future that these swales attract nesting pairs as well.”
Because of water scarcity in a fully allocated basin, open water wetlands have been re-created at only one site but the results are stunning. At the BioPark, excavation to the water table coupled with natural water table fluctuation and native seed dispersal resulted in the establishment of wetland and wet-meadow habitat. “This scarce habitat has provided a haven for waterfowl, no matter the season or time of day,” Austin Johnson said.
By creating a partnership with nature, Austin Johnson and Hummel have re-created far more acreage of self-sustaining habitat in the Middle Rio Grande than they could have otherwise afforded. Monitoring of these projects under an adaptive management paradigm has ensured that the best practices have been identified and replicated in subsequent Albuquerque District projects and those of sister federal and state agencies in the region. Monitoring has shown that these restored environments provide critical habitat for the region’s endangered species.
“This is truly a case of ‘if you build it, they will come’,” Austin Johnson says, “If you enable the river to flood the bosque with something resembling historical seasonal norms, native plants and animals will find their way to this site on their own. Because EWN is so cost-effective, we are able to affect this change at the landscape scale, which is truly exciting to me.”
For additional information, see USACE Engineering with Nature webportal at http://el.erdc.usace.army.mil/ewn/