Lowland reclamation for agricultural development was started 40 years ago in Indonesia. Part of the area is a tidal swamp that originated from marine sediment. Land reclamation by lowering the groundwater table promoted oxidation of acid sulphate soil that produced severe acidity. A tidal irrigation system that allows two-way flow with a reservoir at the end of the channel was introduced at the beginning of development in order to maintain water movement and increase the volume of freshwater flow. After 40 years of reclamation, water and soil quality in several schemes indicate a slow improvement of acidity. After the dry season, acid water with pH 3~4 could be found in the canal, as well as potential acid sulphate soil still found in the shallow layer. Appropriate water management in the scheme should meet at least tree objectives, i.e. supplying enough water for leaching and diluting acid water, draining excess water during storms, and keeping the potential acid sulphate soil under reduced conditions in order to avoid excessive oxidation. Evaluation of the hydraulic performance of the existing main system indicates a need for upgrading of the channel to allow enough fresh water that could support the process of leaching and flushing. RÉSUMÉLa remise en état des basses terres pour le développement agricole a été lancée il y a 40 ans en Indonésie. Une partie de la zone étaient concernée par des marais, soumis à marée et occupés par des sédiments marins. Les travaux de poldérisation, par l'abaissement de la nappe phréatique du sol, favorisent l'oxydation du sol sulfaté acide et produisent une acidité sévère. Un système d'irrigation à deux sens d'écoulement fonctionnant avec la marée et avec un réservoir en bout de canal a été introduit au début du développement, afin de maintenir le mouvement de l'eau et d'augmenter le volume d'eau fraîche. Après 40 ans d'aménagement, plusieurs programmes indiquent une amélioration lente de l'acidité de l'eau et du sol. Après la saison sèche, de l'eau acide avec un pH de 3 à 4 pourrait être trouvée dans le canal alors que du sol sulfaté acide était encore présent dans la couche superficielle. Un système de gestion de l'eau approprié doit satisfaire trois objectifs au moins, à savoir fournir suffisamment d'eau pour lessiver et diluer l'eau acide, drainer l'eau en excès pendant la tempête, et maintenir des conditions réductiques en surface pour éviter l'oxydation excessive du sol. L'évaluation de la performance hydraulique du système principal existant indique un besoin de mettre à niveau le canal pour permettre à une quantité suffisante d'eau douce d'entretenir le processus de lessivage et d'évacuation.
Due to channel sedimentation, water deficits and flood still becomes problems in Katingan tidal irrigation system, while the stakeholder plans to reclaim new area in the presence of pyrite soil. This research aims to overcome these problems through four water management scenarios simulated using HEC-RAS to meet the needs of water supply, flushing and drainage. The result shows that water leaching requirement for existing area is 2.48 million m3 and could only be fulfilled by canal normalization. Moreover, extended network with narrow intake canal supplies less than 4.3 million m3 water leaching, so that wide canal connected to the river is required to facilitate more water flowing into the system. Related to flushing, installing pumps in the middle intake could increase canal circulation with one-way outflow during ebb tide, while the inflow depends on flap gates at the same position. Furthermore, the volume of rainwater is generally able to be discharged for every rainy day by all scenario designs. However, existing condition and network expansion with narrow intake canal have less rainwater deficit duration. In conclusion, leaching and drainage aspects require more water storage and wide canal intake, where flushing criterion need the use of pumps and gates.
Dadahup lowland irrigation area, known in Bahasa as Daerah Irigasi Rawa (DIR) Dadahup, is one of the Ex-PLG areas that has been now included in the food estate program. It has been experiencing low productivity, producing only 1.7 -2.9 ton/ha/year of paddy. Farming on lowland areas is often hindered by inundation during rainy season. Such problems were observed at Blok A5 of DIR Dadahup where inundation might last for a long time. Drainage was hindered since the water level in the channel, being at +1.4 to 1.6 m, was higher than the ground level whose elevations were +1.30 m for the right area and +1.00 m for the left area. Flow simulation by employing HEC-RAS is proposed to obtain a drainage system that can overcome this inundation problem. The use of gates in the secondary and tertiary channels was analyzed to improve drainage performance. The results show that by using gates and pumps can reduce the inundation area and maintain the water level in the channel according to cultivation needs. Such as in tertiary channel, the water level in the right tertiary channel can be maintained at +1.30 m ~ +1.46 m, and that in the left tertiary channel can be maintained at +1.12 m.
Boyong River is one of many rivers originating from Mt. Merapi, flows across three autonomy administrative of Sleman Regency, Yogyakarta City, and Bantul Regency. The river experiences flood in the form of lava flow several times, and the 1994 and 2010 occurrences were considered the biggest ones along with the river history. In line with the rapid development of information and communication technology, efforts to develop the early warning system due to the Mt. Merapi disaster have been implemented by the Hydraulic Laboratory of Gadjah Mada University 2006. This paper presents the study results of Boyong River flow behavior by analyzing the data obtained from the monitoring system. The Gemawang Weir at Boyong River was selected as the river control point understudy; those include the catchment boundary, the catchment characteristics, and the hydraulic features. Monitoring equipment consists of an automatic water level recorder (AWLR), the flow visualization using a Brinno camera, and the hydrophone monitoring system. The flow hydrograph characteristics and its corresponding sediment transport rate are considered two parameters for identifying the flow behavior. The results show that the precursive and recession times of the flood hydrograph are about 1-3 hours and 3.5-5 hours, respectively.
The villages of Sumbangtimun and Kandangan, in the Lower Bengawan Solo River, Java, Indonesia, are regularly flooded. These flood‐prone areas are located in a meander of the river with low natural embankments. Flood damage losses were estimated at US$190 000 in the wet season of 2007/2008, with the largest losses in the agricultural sector, due to floods which came early before the harvest season. In this article, we explore the potential of a set of mini polders for the different types of land use, i.e. rice fields, tree crop plantations and settlements, each with different tolerances to flooding, as an alternative way to manage flood risk. The HEC‐RAS and PondPack hydraulic models were used to design an appropriate mini polder system and its operational procedures. According to the results of the model simulations, the inundation by a flood with a 2‐year return period is about 1 m deep, over 2 days, with 250 ha flooded. The inundation by a flood with a 10‐year return period is about 2.5 m deep, over 3 days, with 383 ha flooded. The models were also used to design a retention pond and pumping capacity. Copyright © 2017 John Wiley & Sons, Ltd.
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