By Aris Fajar Suryono – (Thesis M.Si Sriwijaya University, 2012), Supervised by Prof. Bart Schultz, PhD, MSc; Prof. Ir. Robiyanto H. Susanto, PhD, M.Agr.Sc; F.X. Suryadi, PhD, MSc.

Indonesia is one of the most populous countries in the world. Based on the recent census in 2010, the total population of Indonesia is under China, India, and United States. One of the population characteristics in Indonesian is the uneven growth between islands and provinces. Since 1930, most of the Indonesian population lives in Java Island. Java as the centre of political power and economic is inhabited over two thirds of total population. Population density is the main issue of. The result of the last census shows that total population in Indonesia is about 233 million. Using projection it can be predicted that total population of Indonesia will increase to 273 million in 2025.

Nowadays, the alternative areas for agriculture development in Indonesia especially for paddy field become important issues. Tidal lowland is one of the alternatives to develop as agriculture areas. If Java Island is not able to accommodate population growth in the future, the government of Indonesia must find new locations to be developed. The only suitable locations are on the tidal lowlands which are widely available on the Sumatra, Kalimantan, Sulawesi and Papua islands.

Government and local settlers have been developing for about two million ha of tidal lowlands. The purposes of those developments were for agriculture and settlement. The Government started to reclaim tidal lowland scheme in 1970s. Transmigration, the movement of people from densely populated islands like Java to Sumatra Kalimantan and Papua, was one of the original objectives of tidal lowlands development done by the government. Government schemes are mostly in the first or the second phase. Water control structures in the secondary and/or tertiary canals have been installed in some schemes. The farmers have done various measurements by themselves. Various on-farm and post harvest measures have been taken especially under the Micro Water Management System program of the Ministry of Agriculture.

The water management zoning in tidal lowland schemes is affected by tidal fluctuation. In extreme conditions, rainy season and high tides, some areas in those schemes will be flooded. Those conditions may worsen because of lack operation and maintenance in the canals and inappropriate water control structures. Since lowland development schemes in Indonesia are mostly reclaimed for agriculture development, those conditions will affect the agriculture productivity. In this case, land subsidence will also change the water management zoning in the future.

This research is based on Geographic Information System (GIS) and model simulation. DUFLOW modelling has been used to analyze hydraulic performance for each scenario. MODFLOW modelling has been used to simulate distribution of the groundwater level in the field. Consequently the results of those model simulations has been used in ArcGIS programme to interpolate and analyse spatial data distribution. By using a Geographical Information System (GIS), the water management zoning has been prepared based on land suitability and cropping type in the schemes.

The results of DUFLOW modelling show that the condition of the canal will influence the water level in the canal. With good maintenance, the losses along the canal can be minimized. This condition strongly related to the changes of hydro-topography in the scheme. Prediction of land subsidence can be modelled by subtracting average land subsidence from present topographical condition with. The comparison of hydro-topography caused by maintenance condition and land subsidence will be simulated by using ArcGIS program. Based on hydro-topography classification, water management zoning for each secondary block can be classified. Water management zoning is important to determine the land use suitability for each secondary block.

The results of hydro-topography classification shows that canals maintenance and prediction of 30 years land subsidence will give significant changes on classification, for example area of class A will increase two times after canal maintenance and six times after prediction of 30 years land subsidence. The changes of hydro-topography classes will also give effect in water salinity and drainability which require further research to know its effect on productivity.

The purpose of maintenance is to ensure that the hydraulic infrastructure and facilities are functioning properly. Continuous maintenance is very important to obtain the advantages of the system, especially in the canal, or part of the canal, where the water velocity is low. Growth of the crop weeds are very fast and quickly reduce the water flow velocity to zero and will lead to poor water quality, supply and drainage in the farm land. The availability of special equipment like hydraulic excavators or dredgers will help the farmers maintain their canal. This equipment can be transported easily from one secondary block to another and the efficiency is much higher compare to the traditional way of cleaning by using man power.

Keywords: Water management zoning, land subsidence, lowland development, hydraulic modelling, DUFLOW modelling, MODFLOW modelling, and GIS modelling