How can the effects of the construction of a dam designed for improved water use be estimated in the sub-basin Yarabamba, Peru?

by Theoclea Schwiech

Introduction

The sub-basin of Yarabamba is located in the south of Peru, near Arequipa, in a dry and mountainous area, and includes the villages of Yarabamba, Sogay, Quequeña and Polobaya, where people mostly live out of farming, and thus rely significantly on their irrigation systems.

Problem definition

The irrigation systems are affected by the lack of water during the dry season for lack of storage and by the disparity of water distribution between downstream and upstream sectors, among other issues. To improve their conditions and remediate to water scarcity, a dam will be constructed in the upstream area. The structure would thus level the high variations in river discharges along the year, with the aim of irrigating currently abandoned lands and possibly extend the agricultural area. However, the effects of a dam on downstream uses are not accurately predictable, as it depends on the current situation both on technical and social levels.

Research

The dam is assumed to improve the water efficiency, but the real issue might lay in the current management of the irrigation system itself, thus decreasing the potential of the dam in solving the water issues. To answer this, the research question was divided as follows:

What are the mechanisms (social and technical) behind the implementation of the dam?
Based on what is known at the present, can recommendations on the use of the future dam be given?
How can the study of the behavior of an irrigation system in a micro-basin be carried out, in order to provide the necessary support to the study?
Is it suitable to describe the entire area by focusing on a smaller area in the sub-basin? Is the description of one or more areas representative of the micro-basin?
In what ways is the entire system shaped by human actions and how are they influenced by the system in return?

Results

The objective is the development of the area through the improvement of water distribution during the dry season, by creating a large storage area to distribute water collected during the rainy season.
To give effective recommendations, the system itself has to be considered since several issues do not depend only on water availability but also on social and even political factors.
The study can be supported by the assessment of the irrigation system through the physical infrastructure, the operators and the water users. Tools for water resources planning like WEAP, used in this research, can also help understand current and future situations in terms of water availability.
Differences between areas close to each other are relatively small, thus in this case it is reasonable to consider that one area is representative of other areas.
The farmers have to adapt to the current system by growing crops that resist to the lack of water, and apply certain irrigation techniques due to the low flexibility of the structures and the very small parcels they cultivate. The water users influence the system in many ways, especially in constructing new infrastructure (canals, reservoirs, etc…), and maintaining and operating the system. Upstream users also influence the lack of water in downstream sectors, as they take water illegally.

Conclusions

Although the dam can alleviate the water deficit of the current situation, modifications both in the way the system is managed and in the irrigation infrastructure have to be considered.

Student: T.C.H Swiech

Committee: Prof. Dr. Ir. N. C. van de Giesen, Dr. Ir M. W. Ertsen, Dr. Ir. R. J. Verhaeghe,Ing. C. A. Machicao Pereyra (CAMP SLR)

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