Comparative analysis of rating curve and ADP estimates of instantaneous water discharge through estuaries in two contrasting Brazilian rivers

Abstract

This work quantifies, using ADP and rating curve techniques, the instantaneous outflows at estuarine interfaces: higher tomiddle estuary and middle to lower estuary, in two medium-sized watersheds (72 000 and 66 000 km2of area, respectively), theJaguaribe and Contas Rivers located in the northeastern (semi-arid) and eastern (tropical humid) Brazilian coasts, respectively.Results from ADP showed that the net water balances show the Contas River as a net water exporter, whereas the JaguaribeRiver Estuary is a net water importer. At the Jaguaribe Estuary, water retention during flood tide contributes to 58% of the totalvolume transferred during the ebb tide from the middle to lower estuary. However, 42% of the total water volume (452 m3s1)that entered during flood tide is retained in the middle estuary. In the Contas River, 90% of the total water is retained duringthe flood tide contributing to the volume transported in the ebb tide from the middle to the lower estuary. Outflows obtainedwith the rating curve method for the Contas and Jaguaribe Rivers were uniform through time due to river flow normalizationby dams in both basins. Estimated outflows with this method are about 65% (Contas) and 95% (Jaguaribe) lower comparedto outflows obtained with ADP. This suggests that the outflows obtained with the rating curve method underestimate the netwater balance in both systems, particularly in the Jaguaribe River under a semi-arid climate. This underestimation is somewhatdecreased due to wetter conditions in the Contas River basin. Copyright  2011 John Wiley & Sons, Ltd