Southwestern intermittent and ephemeral stream connectivity

Authors: Goodrich, David - Dave; KEPNER, W.G. - Environmental Protection Agency (EPA); LEVICK, L.R. - University Of Arizona

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2018
Publication Date: 4/1/2018
Citation: Goodrich, D.C., Kepner, W., Levick, L. 2018. Southwestern intermittent and ephemeral stream connectivity. Journal of the American Water Resources Association. 54(2):400-422. https://doi.org/10.1111/1752-1688.12636.
DOI: https://doi.org/10.1111/1752-1688.12636

Interpretive Summary: Maintaining clean water supplies and the human, economic, and ecological systems they support are of paramount importance to the health, economy, and environment of our society. To maintain our systems of clean water it is critical to know how water moves through and is connected across our landscapes and watersheds. Ephemeral and intermittent streams are important in the connection of waterways in the arid and semi-arid landscapes of the West and particularly the Southwest. These areas are characterized by low and highly variable precipitation where potential evapotranspiration exceeds precipitation. Based on the mapping data; 94%, 89%, 88%, and 79% of the streams in Arizona, Nevada, New Mexico, and Utah are intermittent or ephemeral. Connectivity of headwater and tributary streams to downstream waters or rivers in these regions is illustrated with observations and research from the heavily studied San Pedro River Basin and the densely instrumented USDA-ARS Walnut Gulch Experimental Watershed (WGEW); an ephemeral tributary to the San Pedro River. Flows and floods from ephemeral and intermittent streams are major drivers of the dynamic hydrology of the relatively few perennial reaches in the Southwest. These streams also supply water to mainstem alluvial aquifers and regional groundwater aquifers. Both alluvial and regional aquifers, in turn, supply baseflow to perennial mainstem stream reaches over extended periods (sometimes months) when little or no precipitation occurs. This baseflow and shallow groundwater support the limited naturally occurring, vibrant riparian communities in the region. In addition, ephemeral streams export sediment, which contributes to shaping the fluvial geomorphology and alluvial aquifers of streams in the region, and nutrients, which contribute to river productivity. A major conclusion supported by the evidence presented is that intermittent, and ephemeral tributary streams, are physically connected to rivers via channels and associated alluvial deposits where water and other materials are concentrated, mixed, transformed, and transported downstream as well as by dispersal and migration of species that use both habitats during one or more stages of their life cycles.

Technical Abstract: Ephemeral and intermittent streams are abundant in the arid and semi-arid landscapes of the West and particularly the Southwest. These areas are characterized by low and highly variable precipitation where potential evapotranspiration exceeds precipitation. Based on the mapping data; 94%, 89%, 88%, and 79% of the streams in Arizona, Nevada, New Mexico, and Utah are intermittent or ephemeral. Connectivity of headwater and tributary streams to downstream waters or rivers in these regions is illustrated with observations and research from the heavily studied San Pedro River Basin and the densely instrumented USDA-ARS Walnut Gulch Experimental Watershed (WGEW); an ephemeral tributary to the San Pedro River. Flows and floods from ephemeral and intermittent streams are major drivers of the dynamic hydrology of the relatively few perennial reaches in the Southwest. These streams also supply water to mainstem alluvial aquifers and regional groundwater aquifers. Both alluvial and regional aquifers, in turn, supply baseflow to perennial mainstem stream reaches over extended periods (sometimes months) when little or no precipitation occurs. This baseflow and shallow groundwater support the limited naturally occurring, vibrant riparian communities in the region. In addition, ephemeral streams export sediment, which contributes to shaping the fluvial geomorphology and alluvial aquifers of streams in the region, and nutrients, which contribute to river productivity. A major conclusion supported by the evidence presented is that intermittent, and ephemeral tributary streams, are physically connected to rivers via channels and associated alluvial deposits where water and other materials are concentrated, mixed, transformed, and transported downstream as well as by dispersal and migration of species that use both habitats during one or more stages of their life cycles.