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Rio Grande Floodplain and Terraces

Ecoregion in TX

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The Rio Grande Floodplain and Terraces are relatively narrow in Texas, but this region is an important natural and cultural feature of the state. Draining more than 182,000 square miles in eight states of Mexico and the United States, the Rio Grande Basin is one of the largest in North America. The river is generally sluggish and its water flow in this section is controlled in part by two large dams, Amistad above Del Rio, and Falcon below Laredo. The region consists of mostly Holocene alluvium or Holocene and Pleistocene terrace deposits, with a mix of ustic to aridic, hyperthermic soils. Some floodplain forests occurred, especially in the lower portion of the region, with species such as sugar hackberry, cedar elm, and Mexican ash. These species are generally more typical downstream in 34f. Riparian forests have declined as natural floods have been restricted by flood-controlling dams and water diversions. Brushy species from adjacent dry uplands occur at the margins, such as honey mesquite, huisache, blackbrush, and lotebush, with some grasses such as multiflowered false rhodesgrass, sacaton, cottontop, and plains bristlegrass. Wetter areas near the river may have black willow, black mimosa, common and giant reed, and hydrophytes such as cattails, bulrushes, and sedges. Many of the wider alluvial areas of the floodplain and terraces are now in cropland, mostly with cotton, grain sorghum, and cool-season vegetables. The arid or semi-arid climate of the Rio Grande Basin, the over-allocation of actual water, and the difficulties of bi- national management contribute to serious water resource, environmental, and economic issues. Water withdrawals and pollution from agricultural, urban, and industrial sources have degraded water quality. Salinity, nutrients, fecal coliform bacteria, heavy metals, and toxic chemicals are concerns for river uses such as irrigation and drinking water.

— EPA

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