Relevance of Stage and Degradation in Hydrologic Drought Assessment

Keywords: degradation, rivers, fluvial geomorphology, hydrology, droughts, stage, streamflow
Abstract Type: Paper Abstract

Abstract

Rivers are vulnerable during low flow periods because hydrologic droughts cause multiple stresses to aquatic biota and society. The preponderance of the literature examines streamflow as the most important indicator for hydrologic drought, yet there are situations in which natural and anthropogenic drivers moderately impact streamflow but have more notable impacts on stage. Through the application of a case study on the Apalachicola River in the Gulf Coastal Plain of the US, where dam construction and dredging caused degradation, resulting in channel widening and deepening, leading to stage decreases for ~ 30 km downstream of the dam. Degradation-induced lower water levels result in decreased floodplain inundation, reduced river-floodplain connectivity, and disconnected sloughs and backwater floodplain habitats. Besides downstream of dams, stage decreases for the same flow volumes occur in channelized rivers, mined rivers and floodplains, rivers with artificial cutoffs, urbanized watersheds, and many other scenarios. Given that human impacts are often the primary driver for reduced inundation, disconnections with floodplain streams, and resultant ecosystem changes, river scientists examining hydrologic drought should pay equal attention to stage changes as they do to discharge.