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16 I Riparian Ecosystem Recovery Taking Advantage of Available Information Taking advantage of documented information about the degraded riparian area can save ecosystem managers a lot of time, energy, and money. At least some background information is likely to be available. Federal and state agen- cies (see bibliography, list of archives), university libraries, and local private conservation organizations are good places to begin the search. Many areas have been directly studied as part of management plan development, scholarly work, resource inventories, environmental impact assessments, and so forth. If an area has not been directly studied, at least indirect data are likely to be available. Maps, field data, archival sources, and surveys of bridge and pipe- line crossings can provide information describing changes in channel form and independent geomorphic watershed variables. Conservation plans, historical records, and fishing and hunting records can provide information describing past vegetation, wildlife, and fish characteristics. Aerial photographs can aid tremendously in understanding the past condi- tion of the watershed and its associated riparian ecosystems. Comparing his- torical photographs to current versions is a relatively quick and inexpensive way to understand the extent to which the watershed has changed since the mid 1930s (when aerial photographs became available for much of the United States) and the reasons for the changes. Such a comparison can provide infor- mation on rates of agricultural expansion, urbanization (housing, roads, etc.), timber harvesting, grazing activities, and a plethora of other land use ac- tivities, which in turn can help explain the decline of riparian habitat. Nu- merous texts are available on aerial photograph interpretation: two examples that focus on natural resource issues are Verstappen 1983 and Way 1978. Universities and most federal and state agencies have libraries of aerial pho- tographs. The U.S. Geological Survey maintains a central repository of photo- graphs from the United States and many other parts of the world in Sioux Falls, South Dakota. Aerial photographs taken prior to 1945 can be found at the National Archives in Washington, D.C. In addition, most large urban centers have private firms that produce and sell their own aerial photographs. Getting to Know the Watershed A watershed is the area that collects and discharges runoff for a point on a stream. The watershed is therefore defined by the stream that drains it. The terms catchment and drainage basin are often used synonymously with water-