The Rio Grande’s waters would find their way from Colorado to the Gulf of Mexico. The spring snow melt flowed into the Rio Grande joining other river flows along the way and bringing seasonal flood waters to the most southern tip of Texas. The Rio Grande would physically move during large flood events and shift its position, leaving its former channel to become a distributary channel. These channels acted as a conduit for moving water to the Gulf of Mexico and were former locations of the Rio Grande channel. When overflowing its main and distributary channel banks, the Rio Grande would carve new river channels (oxbows) locally known as “resacas.” During high flood events, the Rio Grande delta would have been inundated with slow moving water. As the river retreated, the newly formed resacas and rich soils brought by the flooding would remain. This helped establish the resacas and its lush, tall trees such as Texas ebony, anacua, tepeguaje, sugar hackberry, cedar elm and Rio Grande ash, which make up the majority of the floodplain forest community. From a bird’s eye view the resacas look like a series of unconnected horseshoe-shaped bends that line the final stretch of the river.

With human settlement came the need to curb the flooding, as well as the need to access fresh river water. Soon after, an impressively engineered system of irrigation canals and levees allowed people to prosper on the farming of the rich soils. In 1953, Falcon Dam was built to tame the Rio Grande and prevent flooding in the lower delta of the Rio Grande Valley. It was one of many agreements that would dam and divert river waters further upstream. Today many Resaca’s now serve as storm water reservoirs, irrigation district reservoirs, irrigation channels, residential lakes and farm land. Today, tracts of the Lower Rio Grande Valley National Wildlife Refuge resemble islands in a sea of cleared and altered lands. Each year resacas on the refuge are identified for restoration based on funding, resources on hand, needed management and acreage.  The more than 1,300 acres of resaca and floodplain forest habitat on the refuge remind us of what the land used to look like.

Based on pre-dam hydrologic flow records of the Rio Grande, refuge staff maintain this living piece of history by mimicking the historic flood seasons of the Rio Grande. Pumps, pipelines, valves and adjudicated water rights are used to draw waters from the river and delivered to the resacas and floodplain forests during flow peaks in spring (May – June) and fall (September – October). Conversely, as happened historically, the resaca’s are allowed to dry out at other times of the year. During this time, biologists use an integrated management approach utilizing herbicide, fire, mechanical treatments and active water management to control invasive and exotic plants so that when the waters return, the resacas will be rich with native plants beneficial to wildlife.

During the summer months, resacsa are managed to provide breeding, nesting, brood rearing and feeding habitats for resident species such as mottled ducks, black- bellied and fulvous whistling ducks, rails, gallinules, least bitterns, grebes, moorhens, coots, kingfishers, wading and neo-tropical birds, butterflies, dragonflies, invertebrates, amphibians, reptiles and water dependent wildlife. In the winter, resacas are maintained to provide habitat for resident species and optimal migration stopover, resting and feeding habitats for migrating and wintering waterfowl, wading and shore birds.

While nature did it best, the refuge’s seasonal management efforts ensure continued life for the resacas and floodplain forests.  They provide year-round habitat for birds, watering holes for willdife and homes for a fascinating medley of insects, reptiles and amphibians.