Bendungan Tugu yang termasuk dalam sistem pengaliran sungai Keser dan berlokasi di Kabupaten Trenggalek, Propinsi Jawa Timur telah disimulasikan runtuh dengan menggunakan perangkat lunak HEC-RAS 5.0.1. Sebaran banjir yang terjadi akibat keruntuhan Bendungan Tugu dengan skenario overtopping memiliki dampak yang lebih besar daripada skenario akibat piping atas. Pada skenario piping atas karakteristik banjir di lokasi terpilih yang paling parah adalah Desa Nglinggis pada jarak 500 meter dengan kedalaman banjir 7.26 meter, kecepatan aliran banjir 12.44 meter/detik, dan waktu tiba banjir 40 detik sedangkan pada skenario overtopping karakteristik banjir di lokasi terpilih yang paling parah adalah Desa Nglinggis pada jarak 500 meter dengan kedalaman banjir 7.94 meter, kecepatan aliran banjir 12.44 meter/detik, dan waktu tiba banjir 40 detik. Sehingga dalam analisa sebaran banjir digunakan skenario keruntuhan bendungan akibat overtopping yang secara administratif mencakup 14 Desa, 4 Kecamatan di Wilayah Kabupaten Trenggalek dengan jumlah penduduk yang terkena resiko diperkirakan mencapai 59.925 jiwa. Berdasarkan SK Dirjen SDA PU, tahun 2011 Bendungan Tugu diklasifikasikan Bahaya Sangat Tinggi. Keruntuhan bendungan mempunyai dampak yang sangat besar, sehingga diperlukan upaya pencegahan keruntuhan bendungan. Dari hasil analisa, Bendungan Tugu mempunyai potensi overtopping sehingga dapat memicu keruntuhan bendungan. Rekomendasi pencegahan dengan cara teknis yaitu dengan membuat emergency spillway sebesar 6 meter atau meninggikan tubuh bendungan sebesar 1 meter. Sedangkan keruntuhan bendungan akibat piping dapat dicegah dengan cara menurunkan muka air waduk dibawah elevasi kerusakan bendungan.
Installation of mulch on agricultural land, besides reducing weed growth, can also protect the soil surface from rain and erosion. This study aims to determine the effectiveness of rice straw mulch in reducing surface runoff and soil loss before entering the river. The experimental soil materials were similar to those in Sumber Brantas village, Bumiaji Sub-District, Batu. Runoff modelling utilized the Armfield S12 Rainfall Simulator - Advanced Environmental Hydrology System, with rainfall of 1 and 1.7 l/min. Land with rice straw mulch was compared to land without mulch. The land slope was adjusted to study area conditions, with mild (9%) and steep (15%) slopes. The three-Way ANOVA method was utilized for statistical analysis. In all the experimental runs, it was found that straw mulch effectively reduced the sediment yields that could enter the river area by more than 50%. The results of ANOVA analysis on sediment yield also showed that the significance value of the interactions between slope, rain intensity, and mulch usage was 0 (p<0.05). These results show that the difference in variations in these three factors determines the sediment yield that occurs. In the future, comparing straw mulch with other materials to cover agricultural land should be conducted.
Grawan Dam was built in 2004 to supply irrigation water and raw water. Lately, the dam has experienced various symptoms of damage to the overflow structure due to hydraulic behaviour and the possibility of overtopping of the dam, which endangers the stability of the dam. Therefore, it is necessary to evaluate the overflow structure system based on the current hydrological conditions and to review the slope stability. In this study an evaluation was carried out covering the safety of the slopes as well as the safety of the overflow building system. Dam slope safety was reviewed based on seepage and slope stability. The stability of the overflow structure security system was evaluated in normal and earthquake conditions. The results of the hydrological analysis on guard height, seepage that occurs safely to permit discharge, and slope stability showed 100% safety from permitted safety factors, and on hydraulic conditions resulted in proposed improvements for Vlugter ponds, transition channels, and energy dampers with planning for Q100, Q1000, and QPMF. Analysis for the stability of the overflow structure showed that it is safe against rolling and sliding, and meets the eccentricity and carrying capacity of the soil, being 100% safe.
Banyukuwung Dam is located in the villages of Sukorejo and Sudo, Sumber District, Rembang Regency, Central Java Province. This dam was built in 1995-1997 to serve the needs of 7750 ha of irrigation water and 35 l/s of raw water needs. Dam type is homogeneous reservoir, has a height of 19.40 m above the riverbed and 25.40 m above the foundation excavation. The length of the dam peak is 181.00 m and the width is 5.00 m while the reservoir volume under normal water conditions is 1.64 million m3. Along with seasonal changes and extreme hydrological behavior and based on an investigation of current geotechnical conditions, stability analysis is needed based on these two conditions. It is very important to plan operational and maintenance activities related to the dam maintenance program. So that it is expected to be useful for the relevant agencies in making operational decisions. The purpose of this study was to determine the stability of the existing Banyukuwung dam based on the latest hydrological and geotechnical behavior. The results are expected to provide recommendations in the management, operation and maintenance of the dam manager
Soil erodibility is almost always determined and regarded as a constant parameter that does not change with the climate change. Indonesia has dry and wet seasons which may greatly affected the soil properties. Most erosion models and sediment prediction have been developed based on the soil erodibility factor (K) determined from Wischmeier Nomograph; although soil physical changes due to drying and wetting cycles were neglected. This paper presents the Weischmeier soil erodibility factors affected by the soil properties' change on the drying and wetting cycles. For this particular purpose, the effect of drying-wetting cycle's repetition on undisturbed soil from Manting Basin Mojokerto had been studied. The drying-wetting cycle's processes were repeated 6 times; the properties of the soil specimens were investigated at 1, 2, 4 and 6 cycle. During the drying process, the soil specimens were naturally and gradually air dried; while in the wetting process, the soil specimens were gradually wetted up to their fully saturated condition. The soil properties such as: water content (wc), degree of saturation (Sr), void ratio (e), suction and dry unit weight were measured at every desired conditions. The Weischmeier soil erodibility factors were then determined using Weischmeier Nomograph. The results showed that the soil erodibility factors were almost insignificantly unchanged on the dry condition up to around 90% degree of saturation; but then they were decreased rapidly up to 100% degree of saturation. This is thought to be due that the permeability coefficient greatly increase at nearly saturated condition; this condition change the permeability level from very slow to slow to moderate in the Weischmeier Nomograph.
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