GEOMORPHIC RESPONSE OF A LONG LOW-GRADIENT CHANNEL TO MODERN, DECADES-LONG AND CONTINUOUS BASE-LEVEL LOWERING: NAHAL HAARAVA, THE DEAD SEA

The geomorphic response of channels to base-level lowering dominates landscape evolution, including channels crossing eustatically-emerging continental shelves. The factors governing the processes during base-level lowering remain partially unanswered due to difficulties in the scaling and simulation of physical and numerical models and reconstructing the complex evolution of past channels, particularly under low gradients. Here, we utilize data-rich settings (high-resolution digital elevation models, aerial photographs, and Landsat imagery) of newly incising, kilometers-long, perennial reach of Nahal (Wadi) HaArava, which responds to the rapid and continuous lowering of its base-level, the Dead Sea (>30 m in ~35 years; ~0.5–1.3 m yr^-1). The channel evolves in a nearly flat lacustrine bed of the exposed southern basin of the Dead Sea. Past longitudinal profiles, width, sinuosity, and knickpoint retreat during the last decades were documented or reconstructed. Mouth slopes, delta progradation, and lithology variations are the primary factors controlling the channel evolution. Subject to these factors, we propose a three-stage conceptual channel evolution model at continental margins and resistant over nonresistant substrate setting: (a) Channel lengthening on top of the low gradient of the emerging shelf; (b) Spatially discontinuous evolution triggered by a steeper mouth slope; lithology-induced knickpoint divides the channel into incising, narrow, and meandering reaches downstream of the knickpoint and limited changes in upstream reaches; and (c) Spatially continuous evolution in relatively homogeneous substrate, following a rapid knickpoint retreat phase. We discuss the effect of variations in the governing factors on related channel evolution end-members, characterized by a different pattern of incision.