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Case Study 1 Rincon Creek Determining the Causes of Degradation Rincon Creek drains a significant portion of the west-facing slopes of the Rincon Mountains near Tucson, Arizona. Only 40 years ago, the lower reach of this drainageway experienced aboveground flow most of the year and was dominated by a large Arizona walnut (Juglans major) and mesquite (Prosopis velutina) woodland. Today, this reach experiences flow only in direct response to significant rainfall and is dominated by such species as burro-weed (Aplopappus sp.), burro- brush (Hymenoclea monogyra), ragweed (Ambrosia spp.), and jim- sonweed (Datura stramonium) (fig. 2.1). This reach of Rincon Creek is being evaluated to find out why its condition has changed so dramatically and what can be done to bring it back to health. The bottomlands of lower Rincon Creek are cur- rently grazed by cattle, and preliminary evaluations of this area seemed to point to overgrazing as the major cause of decline. How- ever, when the evaluation was broadened to include other consider- ations, the more pivotal role of other impacts became obvious. Interviews with long-time residents, county records, and old pho- tographs reveal an extensive history of agriculture that goes back to the early 1930s. To make way for the cultivation of alfalfa and barley, the streamside vegetation communities were removed; pumping rec- ords show that these crops relied heavily on irrigation for their sur- vival. Current records of water wells reveal groundwater depths that approach 25 m, far below what is suitable for most phreatophytes. Including Rincon Creek tributaries in the evaluation process and comparing aerial photographs from the mid 1930s to more recent times revealed losses in streamside vegetation communities and the construction of retention basins along many of the tributaries of Rin- con Creek, which prevent the tributaries from directly contributing to flow in Rincon Creek. Data collected from crest stage gauges and scour and fill chains in- stalled along a significant portion of lower Rincon Creek portray an unstable environment that experiences significant aggradation and flashy flow events. In addition, a significant portion of the watershed of Rincon Creek is likely to be extensively developed in the near fu- ture, threatening to further heighten the stream channel's instability. o o o o o