chapter  13
Science and management needs related to the sustainability of riparian ecosystems
ByDianne E. McDonnell, David C. Goodrich
Pages 15

What we term “the Middle Rio Grande” (MRG) begins at the Otowi Bridge stream gage well within New Mexico. The cor ridor extends about 320 kilo meters south to the San Marcial stream gage. Historically the MRG floodplain was a braided, slightly sinuous river that broadly meandered laterally within the 2 km to 6 km wide floodplain (Crawford et al., 1993). The dynamic effects of flooding supported an ever changing mosaic of landscapes including native forests, grassy meadows, ponds, small lakes, and marshes (Crawford et al., 1993). The native forests or “bosque” were dominated by cottonwood (Populus deltoides) and coyote willow (Salix exigua) of varying ages, sizes, and configurations (Crawford et al., 1993, Molles et al., 1998). Today the river is deeper and more constrained. The eco sys tem along the MRG is adversely impacted by the invasion of nonnative species and by changes in climate, land-use, water quality, and groundwater and surface water regimes via diversions, flood control and pumping. The historic landscape along the MRG sup ported human settlements for the past 11,000 years and only became heavily populated about 700 years ago (Riley 1995). The first evid ence of decline occurred after the “Treaty of Guadalupe Hidalgo” in 1848 when Mexico ceded the Amer ican Southwest to the United States of Amer ica (Chavez 2007). Under U.S. management, speculators came to capitalize on the untapped nat ural resources of the MRG (Harris 2007). Overgrazing and deforestation of sur round ing lands within the basin resulted in increased sediment loads, riverbed aggregation, and increased flooding. The rising ground water table sat ur ated cultivated lands. Population increase, par ticu larly in the San Luis Valley in Southern Colorado, created more demand on water resources, which

caused river drying in the southern reaches (Crawford et al., 1993). Uneven water distribution and saturation of valley lands led to the formation of the Middle Rio Grande Conservancy District (MRGCD) in 1925. The newly formed MRGCD approved and implemented a plan for flood control, drainage, and irrigation (Crawford et al., 1993). At roughly the same time, Colorado, New Mexico, and Texas gov ern ments debated Rio Grande water allotments (see Chapters 5 and 8). In 1935, with nego tiations at a standstill, Texas sued New Mexico and the MRGCD. Eventually, the Rio Grande Compact Commission de veloped a proposed schedule of deliveries between Colorado and New Mexico at the state line and by New Mexico and Texas at San Marcial above the Elephant Butte reser voir. Below the Elephant Butte reser voir, the Bureau of Reclamation had already created an allotment program for Texas and New Mexico under the Rio Grande Project. With all par ties satisfied, Colorado, New Mexico, and Texas approved the Rio Grande Compact in 1939 (Littlefield, 2000). Upstream of Elephant Butte was managed only for agri cul ture, flood control, and delivery of water to Texas, catapulting the MRG into a ser ious state of demise. The construction of dams, levees, and Kellner jetty jacks in the mid-1930s channelized the river and defined today’s active floodplain. Constructed drainage resulted in the dramatic disap pear ance of lake and marsh com munit ies, forcing wetland vegetation to migrate to ditches and drains (Crawford et al., 1993). The ensuing flow regime resulted in aging non-regenerating native canopies and invading non-native species. The river moved away from a more nat ural state to a highly engineered and managed sys tem. The MRG con tinued on this trajectory for over a half century before a real shift in management occurred. The 1990s ushered in an era of conservation and a whole new way of thinking. In 1990, the University of New Mexico hosted a “Conference on Global Climate Changes and the Rio Grande Basin.” The parti cip ants recog nized that New Mexico could be harshly impacted by climate change. They re com mended estab lishing the region as a living laboratory. In 1991, a congressionally appointed Rio Grande Bosque Conservation Committee formed to examine the prob lems affecting the Middle Rio Grande bosque and to make re com mendations for its long-term protection (Crawford et al., 1993, Robert 2005). This effort resulted in The Middle Rio Grande Ecosys tem: Bosque Biological Management Plan (BBMP) (Crawford et al., 1993). Shortly there after, the Rio Grande willow flycatcher and southwestern willow flycatcher were put on the endangered species list and the Middle Rio Grande Endangered Species Act Collaborative Program formed. Finally, in 1995, the New Mexico Office of the State Engineer declared the Middle Rio Grande drainage a “crit ical basin” faced with rapid eco nomic and popu la tion growth and lacking adequate technical in forma tion about the avail able water supply (Barolino and Cole 2002). The renewed polit ical inter est and sub sequent funding led to a surge of research and management ac tiv ities implemented by numerous inde pend ent stakeholders (e.g., indi viduals, farmers, envir on mental and com mun ity organ iza tions, universities, and pueblo, city, state, and federal gov ern ments). While still managed for flood

control, irrigation, water distribution, and water delivery to Texas; stakeholders along the MRG gained access to an interdisciplinary view of the sys tem and the polit ical will to manage for eco sys tem integrity.