Method of 210Pb geochronological to estimate sedimentation rate in water reservoir in the Brazilian semiarid region

Abstract

Dams are important reservoirs in semiarid regions providing the needs of the population and agricultural activities in an area in which intermittent rivers predominate. These reservoirs are subject to erosion processes that can cause sedimentation and affect the quality of the water in them. The method of dating sediments using 210Pb is well known and is used to establish a precise chronology of the sediments in places where abrupt changes in sedimentation conditions do not occur. The work aims to determine the sedimentation rate in five main tributary points of the dam located in the semiarid region of the state of Pernambuco, Brazil, using the geochronologic dating of the sediments by measuring 210Pb activity. The method used was the Constant Rate of Supply (CRS) model. Dating coincides with the date of the conclusion of the construction of the dam. The sedimentation rate grew with the increase in depth and presented a decline in both the rate and flow of the sediments over time. The most recent results presented a decrease in sedimentation rates. The greatest occurrence of the sedimentation rate was identified at points located at the entrance of the dam, which could be justified by the reduction in the average speed of final drainage due to the existence of the reservoir itself.