IWRA World Water Congress 2008 Montpellier France
1. Water availability, use and management
Ignacio R. Martín-Domínguez
María Teresa Alarcón-Herrera
Centro de Investigación en Materiales
Miguel de Cervantes 120. Complejo Industrial Chihuahua
31109 Chihuahua, Chih.
flows, Natural flows, Water availability, Water balance, Hydrological assessment
AbstractThe correct determination of natural
flows in a hydrological basin is of great help in defining control mechanisms that would permit the sustainable use of
water resources. The possibility of quantifying the natural flows is conditioned to the existence of historical records of
booth gauged flows and the remainder parameters of the mass conservation equation.
In most basins water is
used for agricultural activity; however, in very few occasions is it possible to have measurements of the water volume
that returns to surface flow after its agricultural use. Therefore, agricultural return flow is commonly quantified as a
percentage of the total water volume used for this activity. When no previous estimates of the agricultural return
flows in the studied basin are available, it is a common practice to use typical values reported in literature, usually
taking the return flow to be between 20% to 50%. This introduces severe uncertainty to the determination of natural
flows in the basin.
The objective of the present work is to propose an alternative method for the estimation of
agricultural return flow in hydrological basins, based on the detection and correction of the anomaly generated by
return flow in the annual hydrogram of monthly mean natural flows.
The method consists of determining the annual
hydrogram of monthly mean natural flow from the available historical hydrometric records and the mass conservation
equation, with no initial consideration of agricultural return flows. If increments in the natural flows are observed
during the dry season, they can only be attributed to return flows. This constitutes an anomaly with respect to the
theoretical hydrogram, and occurs during the dry months with the greater demand of irrigation water (from March to
June in the Rio Florido basin). The anomaly can be corrected by introducing irrigation return flow values (as a
percentage of the volume used for irrigation), until the deformation of the hydrogram disappears. With this procedure
it is possible to determine a return flow ratio to a higher degree of certainity.
In order to exemplify the method
here presented, the middle basin of the Florido river (Río Florido) in the northern Mexican state of Chihuahua was
used. In this basin is located the Irrigation District 103, and has hydraulic infrastructure for the use of surface water in
agricultural production. The results of the developed example case show that the proposed method is consistent with
the values reported in literature, and reduces uncertainty in the estimation of natural flows.