Altar Valley

The Altar Wash drains the eastern slopes of the Baboquivari Mountains as well as the western slopes of the Sierrita Mountains south of State Route 86 and extends to the south over 30 miles to its headwaters near Mormon and Aguirre lakes, which are within the Buenos Aires National Wildlife Refuge. Flood risks vary in Altar Valley, but sheetflow flooding from the tributaries of the Sierrita Mountains is the dominant type of flooding that affects area residents. While sheetflow flooding is generally fairly shallow, it is also very widespread and makes accessing properties difficult due to the prevalence of unmaintained dirt roads. In sheetflow floodplains, it is important to protect homes from flooding and obtain flood insurance, but it is not appropriate to protect entire properties as this makes flooding worse for neighbors. The main stem of the Altar Wash has experienced severe downcutting and has become a deep canyon in some places with the threat of lateral migration being the primary flood risk factor. This watershed, which includes Arivaca Creek, is 356,123 acres and contains 13,086 acres of SFHA, 44,380 acres of locally identi-fied floodplain and 55,404 acres of Pima County Regulated Riparian Habitat.