Temporary Distribution of Discharges and Morphological Changes at Semi-Arid Rivers: the Jaguaribe River in Ceará State, Brazil

Abstract

This research aims to analyze flow frequency and temporal distribution of discharges in order to verify the discharges responsible for the major morphological changes in the Jaguaribe River, considering the Castanhão Dam interferences. Daily flow data from seven stations in the Jaguaribe river basin were used to analysis of the recurrence intervals (IR). The flow permanency was calculated by compartmentalization of intervals of the daily flow average. The suspended sediments discharge correlated to flow permanency showed an approach of the effective discharge, here understood as morphological discharge. The IR results revealed that the largest flows observed in the stations are in quotas above 6m. Quotas were plotting on the transversal profiles and it was observed that Q_1.5 varies between quotas of 1.5m and 4.6m. For Q_2,33 such quotas varied between 3.7m and 5.5m, indicating that this flow get closer of the flow recurrence to bankfull level. Flow permanency indicated that flows below 10 m³.s^-1 predominate in the stations. At the Peixe Gordo station was observed that after the construction of the Castanhão dam, flows between 10 and 20 m³.s^-1 became predominant in the channel. This reflected in changes in the effective discharge in this section, making favorable condition for transportation in this interval. In the other stations the effective discharge flow remained in the range of 100-199 m³.s^-1. Thus, the results indicate that the bankfull discharge do not relevant in the Jaguaribe river morphology, being the flow between 100-199 m³.s^-1 the main ones in the suspended sediments transportation.