ABSTRACT
Map and gauge records of the Indus river reveal a dynamic river which varies significantly through time and with distance downstream. Tectonic disturbance of Indus valley slope is reflected in varying channel planform, channel dimensions, and frequency of flooding. Specific morphologic evidence of tectonic deformation includes: an anastomosing pattern in a reach of backtilt or subsidence, the development of highly sinuous meanders in a region of forward tilting or steep valley slope, a low sinuosity, temporally variable pattern in a subsiding foredeep, and the presence of asymmetrical meanders in a reach of suspected cross-valley tilt. The morphologic variation of the Indus river, plus downstream loss of water and sediment to the alluvial plain, produce a range of flood depths and flooding variability, and temporal fluctuations of water surface elevations. The middle reach of the river near the ancient city of Mohen jo Daro is characterized by great variability of channel and valley morphology, both temporally and spatially. This dynamic behaviour is suggested as a cause for variable rates of sedimentation on the Indus plain. These conditions plus the likelihood of channel avulsion are preferred as reasons for the abandonment of Mohen jo Daro in contrast to those which involve more unusual and improbable tectonic and geormorphic conditions.
