Evaluation of water loss in transit and surface runoff in a Brazilian semi-arid basin

Cristian Epifanio Toledo,João Carlos Mohn Nogueira,Alexandre De Amorim Camargo

doi:10.4136/ambi-agua.2545

Abstract

The objective of this work was to propose and evaluate a model to estimate transit water losses and surface runoff in a Brazilian semi-arid basin, fundamental components in the hydrological studies of the region, such as in the verification of hydrological connectivity. The study area was the Orós Reservoir Basin, located in the state of Ceará. The modeling of transit water loss and surface runoff were developed based on the work of Araújo and Ribeiro (1996) and Peter et al. (2014). In the proposed model, the parameter of loss in transit (k) was estimated at 0.027 km-1 for a section of the river basin, and when simulated for other stretches it provided good flow results at the end of the stretch, obtaining an NSE of 82%. The value of the runoff coefficient was estimated at 3% and when evaluating a spatial variation of this coefficient in the basin, the values varied from 2% to 12%, and the use of specialized runoff coefficient (RC) values promoted a higher NSE in the discharge simulation in the basin. It is concluded that the proposed model to estimate transit water losses and surface runoff demonstrated a high efficiency in the simulation of hydrological processes. The basin of Orós reservoir presented a high variability of the coefficient of surface runoff, justifying the need for a greater spatiality of this coefficient in heterogeneous environments.

Highlights

The Brazilian Semiarid region has been regularly impacted by drought
In other parts of the world (Gooseff et al, 2017; Ayalew et al, 2017), dense reservoir networks have been studied using hydrological models, and those studies have emphasized that these networks have been causing interference in water discharge dynamics, by increasing the risk of cascading dam failures and provoking the disruption of hydrological connectivity
The losses in transit were considered proportional to the flow in the river and estimated according to the modified equation of Araújo and Ribeiro (1996) (Equation 1), which is based on mass balance and considers that the withdrawals and water loss are distributed along a watercourse, making it possible to estimate the flow at the end of a river stretch

Summary

Introduction

The Brazilian Semiarid region has been regularly impacted by drought. On average, one severe drought occurs per decade; and sometimes, it occurs continually for many years, which leads to conflicts over water use. Political decisions prioritized the construction of reservoirs, and in Ceará, for example, in only one hydrological basin of the state (Alto Jaguaribe), 4,717 public and private reservoirs were identified in 2011 (Toledo et al, 2014). This policy of dam construction produced a “high-density reservoir network”, predominantly composed of smalland medium-sized reservoirs, which consists of a system whose management is complex (Mamede et al, 2018). In the semi-arid and arid regions the conceptual model of hydrological connectivity is more difficult to achieve and occurs less frequently due to limitations like the losses in transit of the runoff (Bracken and Croke, 2007)

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Conclusion