Jemelak Sub Watershed is close to the junction of two big rivers, i.e., Kapuas and Melawi. Therefore, this location faces environmental issues such as a flood. To avoid its possible damages, information on peak discharge becomes critical, particularly in calculating the drainage structure. This study was aimed to predict the peak discharge in this area using a rational method. The maximum daily rainfall data from 1998 to 2017 were divided into two periods of 10 years and analyzed. In the first period,  maximum rainfall rangesfrom98.6 to 176.3 mm, while the second period fluctuates from67.6 to 190 mm. Analysis of land cover described that 43.97% of secondary swamp forests turned into shrubs and swamp shrubs in the first period. Furthermore, about 800.71 ha of secondary swamp forest tuned into 582.80 ha of bare land, 181.04 ha of a plantation, and 36.88 ha of swamp shrubs in the second period. About 95.15% of shrubs were also turned into agricultural land mixed with shrubs in the second period. The result showed that the changes in the maximum daily rainfall and land cover simultaneously affected the improvement of the peak discharge by about 2.53% in the first period and 28.30% in the second period. If the peak discharge exceeds the river capacity, then the local flooding will occur along the river border. Keywords: land cover, peak discharge, rainfall, Jemelak

Soil erosion and sedimentation are environmental problems faced by tropical countries. Many researches on soil erosion-sedimentation have been conducted with various results. Quantifying soil erosion-sedimentation and its temporal distribution are important for watershed management. Therefore, a study with the objective to quantify the amount of suspended sediment from catchments under various pine plantation areas was conducted. The research was undertaken during 2010 to 2017 in seven catchments with various percentage of pine coverage in Kebumen Regency, Central Java Province. The rainfall data were collected from two rainfall stations. A tide gauge was installed at the outlet of each catchment to monitor stream water level. The water samples for every stream water level increment were analyzed to obtain sediment concentration. The results showed that monthly suspended sediment of the catchments was high in January to April and October to December, and low in May to September. The annual suspended sediment fluctuated during the study period. Non-linear correlations were observed between suspended sediment and rainfall as well as suspended sediment and percentage pine areas. The line trend between suspended sediment and percentage of pine areas showed that the increase in pine areas decreased suspended sediment, with the slope of the graph is sharp at the percentage of pine areas from 8% to 40%, then is gentle for pine plantation areas more than 40%.

PENGARUH PERSENTASE PENUTUPAN HUTAN TERHADAP DEBIT PUNCAK DI SUB DAERAH ALIRAN SUNGAI HUTAN ALAM KABUPATEN TANAH LAUT(The effect of forest coverage percentage on peak discharge in the natural forest sub watershed, Tanah Laut Regency) ABSTRACTThe percentage of forest coverage holds an important role in regulating water in watersheds. This paper studies the influence of forest coverage percentage on peak discharge in sub watersheds with various percentage of natural forest areas. The study took place in Bakar, Tanjung, Iwakan, and Langsat Sub Watersheds, Tanah Laut Regency, South Kalimantan Province in 2017. The percentage of natural forest varied from 9,7 to 98% of the the sub watershed areas. This research was conducted by direct measurement of rainfall and stream water levels that were converted into peak discharge. The peak discharges between sub watersheds were compared to the rainfall and the percentage of forest. The results showed that in general the percentage of natural forest coverage affect the peak discharge. The forest coverage showed a positive response in lowering the peak discharge when the rainfall was below 115 mm/day. Bakar and Tanjung Sub Watersheds that had low percentage of natural forest coverage had higher peak discharge than Langsat and Iwakan Sub Watersheds, which had higher percentage of forest coverage. The relationship between the percentages of natural forest coverage with peak discharge marked by the coefficient of determination value of 53.3%. Since the existence of forest is very important as the hydrological controller, forest conservation efforts and reforestation should be conducted in the upper sub watersheds. ABSTRAKPersentase penutupan hutan memegang peran penting dalam mengatur tata air Daerah Aliran Sungai (DAS). Hutan dengan fungsi hidrologisnya berpengaruh terhadap debit sungai. Penelitian ini bertujuan untuk mempelajari pengaruh persentase penutupan hutan terhadap debit puncak di sub DAS hutan alam. Penelitian ini dilakukan pada tahun 2017 di Sub DAS Bakar, Sub DAS Tanjung, Sub DAS Iwakan, dan Sub DAS Langsat, Kabupaten Tanah Laut Provinsi Kalimantan Selatan. Persentase hutan alam bervariasi dari 9,7 sampai 98% dari uas sub DAS. Penelitian dilakukan dengan pengkuran langsung data curah hujan dan tinggi muka

Drought has become a severe disaster faced by several regions in Java, Indonesia due to land cover changes including forest conversion and the increase in air temperature. In this regard, the availability of forests related to lowflow has been a controversial debate. Forest in Java is dominated by teak; however, the hydrological teak forest has not been well known. Therefore, a research has been undertaken to know the baseflow and low-flow of teak catchments covered by various old teak forest areas. The research areas were in