By Rahmat Ruzniar – (Thesis M.Si Sriwijaya University, 2013). Supervised by Prof. Charlotte de Fraiture Ph.D., M.Sc. (UNESCO-IHE), Prof. Ir. Robiyanto H. Susanto, M.Agr.Sc., Ph.D (Sriwijaya University), F.X. Suryadi, PhD, MSc (UNESCO-IHE)

Bintang Mas located in Kubu Raya Regency of West Kalimantan Province is agricultural area that expected to be one of the food producers for Indonesia. In order to realize the objective, developments of water management system have been applied in the area. Though the development has been done, agricultural production in the respective area still low which might be caused by low performance of the irrigation system. Hence, analysis and evaluation of water management system as well as irrigation practices in field level need to be conducted in order to assess performance of the system to increase agricultural production.

Specifically, the objectives of analysis and evaluation of Bintang Mas Water Management System are:

• To analyze the existing hydraulic structures and irrigation practices and to identify the factors that might lead to low performance;
• To evaluate the existing operation and maintenance rules of water delivery and drainage system in the scheme at secondary and tertiary canals level;
• To formulate some possible approaches at secondary and tertiary levels to improve the performance in order to obtain the optimum crop production;

To achieve the objective of the study, two computer modelling had been used to evaluate the current performance of water management system as well as the irrigation practices applied by local farmer. The CROPWAT was used to evaluate the existing performance of irrigation practice regarding to crop water requirement. On the other hand DUFLOW modelling was used to assess the performance of water management system in secondary and tertiary canal. More over the result of DUFLOW simulation was compared to result of CROPWAT in order to make sure the crop water requirements could be fulfilled by the water management system.

Two scenarios were formulated in CROPWAT modelling, the first scenario calculating crop water requirements for existing cropping pattern while the second scenario calculating crop water requirements for improved cropping pattern. On the other hand, three scenarios of DUFLOW were used to evaluate performance of Bintang Mas Water Management System. The first scenario evaluating the performance for supply condition in dry season, the second scenario evaluating the drainage condition in wet season and the last scenario modelling the performance of improved water management system both for supply and drainage condition.

From CROPWAT calculation the net irrigation requirements are 128 mm/year and 168 mm/year for the first and the second scenario respectively. The peaks demand of supply discharge is 0.17 m3/s and 0.23 m3/s for the existing cropping pattern and for improved cropping pattern respectively. Moreover, the result of DUFLOW modelling is shown that tertiary canal with the highest Distribution Performance Ratio (DPR) found in TR 9 and TR 11 (4.4 for existing cropping pattern and 3.9 for improved cropping pattern). Based on the water level during supply condition in dry period, two tertiary canals, TR 19 and TR 21 are unable to meet water level requirements both for maize and rice. Inundation is found in wet season both for extreme rainfall with return period 5 years (5 tertiary canals) and 10 years (7 tertiary canals). Improvement of water management include flap gate installation, removing dead end canal and new dimension of the gate is proved effective to maintain water level 0.6 m+PRL and to remove the excess water in the tertiary canal.

Keywords: Bintang Mas Water Management System, CROPWAT, DUFLOW, rain fed irrigation, crop water requirements