Hydraulics And Irrigation

[Berenice Pretlow]

Irrigationsystems were clearly important in ancient times in supplying crops with water. This requires physical distribution facilities and socio-political arrangements to coordinate between actors. Resulting systems are highly diverse, and are being studied extensively within archeology and history. Whether initiated by a central authority or emerging from small-scale initiatives, irrigation systems are shaped through activities of individuals, households, and small groups into patterns and landscapes. This article discusses how hydraulic modeling techniques are powerful methodologies to study such irrigation development. Modeling daily interactions by agents and water fluxes will build better understanding of irrigation systems as anthropogenic landscapes. Three case studies will be used to illustrate this argument. A current irrigation system in Arequipa, Peru, shows that one can relate irrigation infrastructure and social action. A second case from Peru on a pre-Colombian irrigation system suggests that one can link irrigation system, water flows, and settlement. In the third case in the Jordan Valley, this possible link between irrigation and settlement is further studied.

In order to produce a food surplus for their population, many civilizations in world history used irrigation. Intensified production provided a relatively secure food source for a larger population as it enabled the peasant population to produce a surplus to support the non-peasant population. Food security enabled development of urban kingdoms in many regions: Mesopotamia, Egypt, the Indus-valley, China, Mexico, and (coastal) Peru (Scarborough 2003). The well-known hydraulic hypothesis of Wittfogel (1957) links the development of civilizations to manipulation of water from larger streams for irrigating areas without reliable rainfall (see also Scarborough and Isaac 1993). Although the viability of framing such direct links between water flows and social power may be discussed, it is clear that irrigation links water, humans, and infrastructure in producing an actual water transformation process. In canal irrigation, fields downstream along a canal are potentially at the mercy of the area upstream. If people upstream decide to close the tap, people downstream have serious problems. Although water distribution, canal management, and hydraulic properties are complex issues, and conclusions are not as straightforward as it seems in terms of upstream or downstream relations, it is also clear that canal irrigation is potentially hierarchical in nature (Ertsen and Van Nooijen 2009; Lansing et al. 2009).

Irrigation systems, spatial conglomerates of built elements, are supposed to supply crops with water. This requires both physical distribution facilities to transport water and socio-political arrangements to coordinate between actors in dealing with water flows. Resulting systems are highly diverse. One only has to imagine the terraced rice fields in Asia, the large-scale irrigated plains of the western USA, or the small irrigated gardens in west-Africa to realize that the typical irrigation system does not exist. All irrigation systems are special, but they do share certain characteristics. Any irrigation system needs a source for its water. To divert water, an intake structure is needed. This can be an open canal, a weir, or a bucket. From the intake structure, a canal(s) bring(s) water to the irrigated area. Many irrigated areas have a certain hierarchy of canals, with larger (main) canals bringing water to diversion structures, with smaller (distribution) canals branching of from this structure to bring water to designated areas via smaller (lateral) canals. Drainage removes water from the irrigated area. Regularly, drainage water is used by irrigators downstream, directly or through the groundwater. User strategies have an impact on the system and the system constrains user actions. Hydraulic behavior of irrigation systems resulting from human action is partly constraining and partly enabling human action. Irrigation systems have structuring properties (Ertsen and Van Nooijen 2009; see Sewell 2005; Giddens 1984).

This article will outline this strategy using three case studies. The details available for analysis in each case study become less with each case. I start with an analysis of a current irrigation system in Arequipa, Peru. This case study does show that one can relate irrigation infrastructure and social action. After some remarks on theoretical and methodological implications from this first case, a second case from Peru is introduced. This case deals with the pre-Colombian irrigation system on the Pampa de Chaparr. The results from this case suggest that one can link irrigation system, water flows, and settlement in the area. In a third case, from the Zerqa triangle in the Jordan Valley, this possible link between irrigation and settlement is further studied. I will end this article with some general conclusions and an outlook for further research. However, first we move to Arequipa, Peru.

The city of Arequipa is the capital of the province with the same name in south Peru. The city has an average elevation of approximately 2380 m above sea level. Furthermore, Arequipa has approximately 900,000 inhabitants, making it the second largest city of Peru. The irrigation system in Arequipa is managed by three organizations: the Administracin Tcnica del Distrito Riego (ATDR), the Junta de Usuarios, and several Comisines de Regantas. The irrigation system in Arequipa is under the jurisdiction of the Chile department of the ATDR department, a governmental organization. The ATDR regulates the daily discharge in the river Chili in consultation with other stakeholders, and is concerned with conflict management within the irrigation system. The area supervised by the ATDR is divided in two districts each managed by a Junta de Usuarios (Chili zona Regulado and Chili zona no Regulado). The district Chili zona Regulado is divided in fifteen Comisin de Regantas. Finally, the level of Comit de Canal, seen in the north coast of Peru (Vos 2002), is absent in Arequipa.

The Junta de Usuarios is a federation of all Comisiones de Regantas in an irrigation district. The main tasks of the Junta de Usuarios are operation and maintenance of the primary canal and conflict management at primary and secondary level. In addition, the Junta is concerned with the planning of the water allocation for next year. A Plan de Cultivo y Riego is set up to give a detailed guideline for efficiently allocating water. In the Plan, the water demand per plot is calculated. However, some farmers do not fully participate in announcing which crops they are cultivating, and discharge records are hardly available. As a result, the Plan is not too accurate and therefore not applicable at the level of the Comisin de Regantas. A Comisin consists of farmers from the region and external employees. The main tasks of a Comisin are water allocation and maintenance of canals at secondary and tertiary level. Furthermore, the Comisin is concerned with conflict management within the tertiary block. Comisiones de Regantas have two water guards to check all water structures within the area. Technical problems are directly transferred to the Junta de Usuarios.

To find out how irrigation actually works in this area, three Comisiones de Regantas will be discussed in more detail, Acequia Alta Cayma, Zamcola, and Alto Cural. An intensive fieldwork campaign was conducted in the period between September 2007 and March 2008, including interviews, canal measurements, and participatory observations. This fieldwork was supported by hydraulic modeling.Footnote 1 The three Comisiones cover approximately 2600 ha which represents 35% of the total irrigated areas in the district Chili zona Regulado. With approximately 2100 water users, the average plot size in the area is 1.24 ha. As Table 1 shows, however, differences between Comisiones are considerable. The irrigation water from the river Chili is supplied to the Comisiones by one main canal. This Canal Madre Zamcola starts at the river Chili, runs along Acequia Alta Cayma, through Zamcola, and ends up at the head of Alto Cural (Fig. 1). The average discharge at the inlet of Canal Madre Zamcola is approximately 4.2 m3/s. Between Acequia Alta Cayma and Zamcola an offtake is located which retrieves 1.5 m3/s for the preparation of domestic water. This leaves approximately 2.7 m3/s for irrigation, which is about 1 l/s per hectare.

In terms of profitability of agriculture, benefits are not equally spread either. Although Acequia Alta Cayma has the benefit of ample water supply, its small plot sizes make profitable agricultural practices less possible. The small plot sizes are probably caused by a long history of inheritance. From the scarce data available, one can observe declining farm sizes in all three area between 2001 and 2007. As Alta Cayma is by far the oldest system, probably predating the Spanish conquest, this fragmentation process would have been long. Due to a low profitability from their small plots, most farmers in Alta Cayma perform other activities, and do not give top priority to their agricultural practices. Their level of involvement in participating in irrigation management is very low as well. Tax recovery of Acequia Alta Cayma is a little over 60%, which may indicate unwillingness of many farmers to pay the water tax. Furthermore, land use in Acequia Alta Cayma is changing rapidly. Plots are sold for urbanization purposes. Nevertheless, water needs in Acequia Alta Cayma can be dealt relatively easy. There is room to allocate more water to the farmers than prescribed in the Plan de Cultivo y Riego.

In Zamcola, farmers are generally satisfied with the water availability and the way it is allocated, although sometimes they encounter water shortage, especially from August to October. Up to 90% of the farmers pay the water tax. The facilities of the Comisin de Regantas for the water guards were more extensive in relation to the other Comisin de Regantas. For example, the water guards had motorcycles and offices. In Zamcola the Plan de Cultivo y Riego is taken very seriously. It is used to check the water use of farmers and farmers use it to decide the crop they want to cultivate. The Comisin de Regantas Zamcola has assisted the farmers via facilities for storage, for example, cooling cells, and establishing a good relation with the buyers of the agricultural products. Finally, most products of Zamcola have a quality label, on which the farmers and the president are very proud. Quite a few farmers in Zamcola have constructed their own farm reservoirs to deal with unpredictable water availability. Apparently, there is enough water available on average to construct these devices. Since the reservoirs are paid for by the farmers, it indicates that farmers have enough resource to install them.

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