Impact of cascade reservoir on continuity of river water temperature: a
temperature trend hypothesis in river
Abstract
Water temperature is an important habitat factor in river ecosystems
that exhibits the characteristics of continuous change. Dam construction
disrupts the continuity of the water temperature and reset it, thus
exerting range reduction and hysteresis effects on the characteristics
of water temperature change. The effect of a dam on river continuity is
directly related to the dam size. To explain this relationship, two
rivers in China were selected: one river without reservoirs and one
river with cascade reservoirs. Through the analysis of the longitudinal
change of water temperature in free-flowing rivers, we found that water
temperature changes continuously and uniformly in the longitudinal
direction. Based on this, a temperature trend hypothesis in river was
proposed, and the discontinuity of the water temperature in the
reservoir section was evaluated. The result is as follows: (1) In mixed
reservoirs, river water temperature remained as continuous as
free-flowing rivers. However, the river water temperature had a large
discontinuity in the stratified reservoir; (2) Water residence time was
used as an indicator of the continuity of reservoir water temperature;
(3) Selective withdrawal of stratified reservoirs in January could not
remove the discontinuity caused by itself, but it worked in June.