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USGS NRP Tucson: Landscape Change in the Southwest

Repeat Photography at Gaging Stations
Changes in Riparian Vegetation in Arizona

Introduction

Repeat photography, or rephotography, is a technique in which the exact location of a historic photograph is precisely determined and a new photograph taken that shows the same field of view. By comparing the original photograph with the new image ( also called a photograph match or matched photo), changes to the landscape over time can be identified. Repeat photography is invaluable for documenting and assessing changes in riparian vegetation, plant demography, geomorphology, fire effects, climate, and river channels, among other features.

As part of the regular operation of surface-water gaging stations in Arizona, photographs are taken to document channel conditions. The photographs show many features of the channel that are important to accurate streamflow gaging, including shifts in channel thalwegs or deepest point in the channel, changes in low-water controls, and changes in channel roughness. Photographs have been taken since gaging stations were first established in Arizona in the 1910s, and many photographs were taken in the 1920s and 1930s.

Now, these repeat photographs provide an invaluable record for evaluating changes in the riverine environment of the major water courses in Arizona. Riparian vegetation in particular is highly valued, and its long-term status is much debated. Water development is frequently blamed for decimation or elimination of riparian ecosystems. Floods may damage or destroy vegetation within channels, and channel changes may cause damage to floodplain structures, agricultural fields, and water- and irrigation-supply systems. Increases in channel roughness may create higher stages during floods, raising the possibility of increased frequency of flood damage.

Repeat photography at gaging stations documents long-term changes in the riverine environments of Arizona. The images shown here are selected to illustrate the range of changes, which include large increases in native and non-native vegetation at most sites, complete elimination of riparian vegetation at some sites, channel downcutting, lateral channel changes, and deposition of new fluvial terraces. The causes of many of the changes are not obvious; for example, at some sites, riparian vegetation has increased despite the occurrence of large floods or significant flow regulation. Despite the 20th century spread of tamarisk along the state's rivers, native species have increased as well.

Relief map of AZ showing selected stations with repeat photographs. Link to Virgin River page. Link to Paria River page. Link to Salt River near Chrysotile page. Link to Gila River at Kelvin page. Link to San Carlos River near Peridot page. Link to Gila River at Calva page. Link to Gila River near Clifton page. Link to Gila River below Blue Creek page. Link to San Pedro River At Charleston  page. Link to San Pedro River at Palominas page. Link to Santa Curz River near Lochiel  page. Link to Pantano Wash near Vail  page. Link to Santa Cruz River at Tucson page. Link to Salt River near Roosevelt (09498500) page. Link to Sabino Creek near Tucson  page.

Please note that the Desert Laboratory Repeat Photography archive has been moved to the GCMRC Library in Flagstaff, AZ. Please contact Meredith Hartwell at mhartwell@usgs.gov if you need further information about the collection.

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