Coupling GIS and a Hydro-Dynamic Hydraulic Model for Spatial Analysis of Canal Water Supply Performance

Marcel Kuper
International Irrigation Management Institute, 12 KM, Multan Road, Chowk Thokarniaz Baig, Lahore 53700, Pakistan

Pakistan is facing an increasing gap between its domestic agricultural production and the demand for food stuffs, caused by an elevated population growth rate (at 3%) and a low and stagnant agricultural productivity. One of the causes explaining the low agricultural productivity- is poor canal water supply performance. Contrary to the design concept of the irrigation system in Pakistan, canal water deliveries are inequitable and not very reliable, due to increased pressure on water, a decline in maintenance standards, and chaotic operations related to opaque operational rules, an increasing interference of water users in water deliveries and a decline in credibility of the irrigation agency.

Irrigation water supply performance in Pakistan has mainly been analysed in terms of its punctual (one value for a given irrigation system) or unidirectional (from the head to the tail of a single canal) dimension. Although this may be sufficient from a strictly hydraulic point of view, it is of more limited interest when looking at the impact of canal water supply on the output of an irrigation system such as the productivity of agricultural production and its sustainability.

The paper presents the first results of a study on canal water supply performance that links a hydro-dynamic hydraulic model with a Geographical Information System (GIS). This offers appropriate ways to further comprehend the spatial dimension of irrigation water supply performance. The study has been undertaken in the Chishtian sub-division a large hydraulic unit of 67,000 hectares in southern Punjab. Pakistan, as part of a collaborative effort between the International Irrigation Management Institute (IIMI) and the Irrigation Division of the French research institute Cemagref.

The initial diagnosis phase has led to the identification of management interventions that would lead to improvements in canal water supply performance. The hydro-dynamic hydraulic model SIC (developed by Cemaref) is applied at the main canal and secondary canal levels to quantify the impact of technical and managerial constraints related to the current status of the irrigation system. Following the hydraulic logic of the irrigation system (no control structures have been provided below the inlet structure of the secondary canal), the management interventions focus on alternative rules at the main canal level and alternative maintenance measures at the secondary level. A GIS is developed for the Chishtian sub-division, taking the tertiary unit (watercourse) as the basic unit of analysis. There are a total of 470 watercourses in the study area.

SIC and the GIS are then linked for the spatial analysis of the canal water supply performance at the level of the tertiary unit (watercourse), as a function of changes in main system operation and secondary canal maintenance. The most important part of this analysis is the classification of these variables, resulting in identification of groups of watercourses with corresponding characteristics in terms of canal water supply performance. This classification is an important step to identify scenarios for improvements, which is the output of the initial diagnosis phase. The classification is further developed into a more general watercourse typology by including all irrigation related data (physical variables. socio-economic variables, agricultural production, salinity, etc.). This watercourse typology will also be used in later stages of the research when linking the GIS with other research studies, as mentioned in the final section of this paper.

The impact of selected scenarios is presented and analysed. using the GIS output along with aggregated performance indicators for the Chishtian sub-division. The usefulness of coupling SIC and the GIS is discussed from an operational point of view (irrigation system managers) as well as from an analytical point of view (researchers).

The final section of the paper proposes follow-up activities in the context of a larger integrated approach focused on the development of a methodology to estimate the impact of changes in irrigation management on agricultural production and the environment (mainly salinity and sodicity). This relates mainly to the development of links with micro-economic (linear programming) models an a hydro-dynamic solute transport model.