Active River Areas

Recognizing that the ecological and biodiversity values of streams are closely tied to the dynamic interaction between water and land, The Nature Conservancy has developed the concept of the Active River Area (ARA) to describe some of the physical and ecological processes that drive and sustain a stream, and to provide a conceptual basis for restoring and conserving the landscapes most essential to the functions of stream ecosystems. Active River Areas include the stream itself and the present and past floodplains and adjacent areas that protect, nourish, and accommodate the stream during normal flow conditions as well as during extreme droughts and floods. Riparian corridors and Active River Areas are different ways to consider and delineate critical zones near streams. In addition to the “base zone,” which includes all the areas that flood at frequent or infrequent intervals, the ARA includes the following major components: material contribution zones, which regularly contribute organic and inorganic (e.g., sediments, water) material to streams; meander belts, the lateral areas within which the channel migrates over time; floodplains, the streamside areas that flood regularly or episodically; riparian wetlands; and terraces, the former floodplains that may still flood in the largest flood events. The contributions of these components encompass the major processes influencing the stream— system hydrology, sediment transport, processing and transport of organic materials, and key biotic interactions—all useful concepts when considering effective measures for stream conservation. (The ARA zones are based on coarse elevation data, and have not been field-verified.) www.conservationgateway.org/ConservationByGeography/NorthAmerica/UnitedStates/edc/reportsdata/freshwater/floodplains/Pages/default.aspx