Hydrological Effects of Dam Construction

Hydrological Effects

The construction of a dam is usually responsible for profound changes in the hydrology of the stream, both regarding the system of flow and sediment transport.

Changes in Flow Regime

The construction of a dam substantially alters the flow regime upstream since it changes a particular stretch of river with flowing water into an artificial lake. As a result, the formation of the reservoir causes changes in the water table around the lake, these being more or less significant changes, according to the variation of the water level in the reservoir over time. This can cause problems with slope stability periodically immersed in the foundations of buildings near the reservoir, the water supply wells in agricultural areas in the river, and remnant natural vegetation.

In addition, following the formation of the reservoir, there will be an increased inflow during wet periods. This is due to the decreased attention span of the basin, reducing distances because the water must travel and the growth of the liquid surface in which water is transformed, precipitated instantaneously in contribution. In dry periods, there will be a reduction in flow due to increased evaporative loss.

With the accumulation of tributaries in the reservoir volume to meet the demands, the surplus in the rainy season released downstream will suffer a buffer and in the dry season, an increase. In most years, this effect will be noticeable, and only in extremely wet or dry years, the effect may be zero or negative. Another change in the downstream system must occur during the filling of the reservoir when, for some time, little or no flow is released downstream.

Changes in Sediment Transport Regime

The construction of a dam creates conditions for a large amount of solid material carried by the river upstream to be deposited and, therefore, decreases the amount of material transported downstream. As a result of this phenomenon, there is the loss of fertile land along the banks downstream. During the small streets, they were flooded and therefore benefited from the deposition of organic material.

The oscillation of the water level in the reservoir, depending on its operation, may cause the collapse of its banks, which can cause increased silting of the reservoir and, therefore, a decrease in its life.

Erosion processes downstream of the dam depend basically on the physical properties of the materials making up the bed of the river and discharged flows and its erosive power, taking into account the reduction of suspended solid material tends to increase. Thus, it is possible to have erosion on the banks of sand, natural beaches, and in the very bottom of the bed of the river along a stretch downstream of the dam.