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abstract 550

Natural flows determination in gauged hydrological basins (Part I)

Author(s): Alternative method for irrigation return flows estimation
Author(s): Humberto Silva-Hidalgo, Ignacio R. Martín-Domínguez, María Teresa Alarcón-Herrera, Alfredo Granados-Olivas
Centro de Investigación en Materiales Avanzados, S.C. Miguel de Cervantes 120. Complejo Industrial Chihuahua 31109 Chihuahua, Chih. México. +52-614-439-1148 ignacio.martin@cimav.edu.mx

Keyword(s): Irrigation return flows, Natural flows, Water availability, Water balance, Hydrological assessment

Article:

Poster:

Session: Poster session 2

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.

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Natural flows determination in gauged hydrological basins (Part I)