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| Title | Implementasi Kaji Cepat Hidrologi (RHA) di Hulu DAS Brantas, Jawa Timur | | Author | Widianto, Didik Suprayogo, Sudarto and Iva Dewi Lestariningsih | | Year | 2010 | | Publisher | World Agroforestry Centre - ICRAF, SEA Regional Office | | City of Publication | Bogor, Indonesia | | Series Number | Working paper nr.121. DOI: 10.5716/WP10338.PDF | | Number of Pages | 133 | | Call Number | WP0152-11 | | Keywords | Environmental services, hydrological, modeling, local knowledge, watershed |
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| Abstract: |
| Sumber Brantas Watershed is one out of five sub catchments of the Upper Brantas River, situated in Batu District, East Java, Indonesia and covering an area about 174 km2. Recently, the hydrology of the watershed was considered to be degraded in terms of the quality and quantity of water yield. Fast floods were more often during the rainy seasons, while droughts were more severe during the dry seasons. Much spring water dried out in the dry seasons and two-third of them dried out permanently in the last decade. The condition was often related to the rapid change of landuse in the watershed. The natural forest and agroforestry gardens were converted into rain fed agriculture. Analysis on land sat images from 1989 and 2002 showed that 3,702ha of natural forest and 1,153ha of agroforestry gardens has disappeared. Further analysis showed that the area of rain fed agriculture, settlements and shrubs were increasing during that period. This most likely related to the socio-economics conditions of local community as well as the variability of stakeholders? perception in best watershed management planning and practices.
The Rapid Hydrological Appraisal (RHA) implementation at the Sumber Brantas Watershed aimed to test the methodology, which is claimed to be rapid and cheap, and to validate the GenRiver Model – an important component of the methodology, to learn the stakeholders? perceptions on the watershed management and to build an understanding among stakeholders in order to select the best watershed management practices.
RHA itself is claimed as a rapid and cheap methodology that is important in the early steps of an environmental service activity. The method consists of three stages i.e. scooping, awareness and identifying partners. Scooping and identifying partners were reflected from information and data collection about study site, hydrological issues, and stakeholders who involved in the watershed management.
Watershed stakeholders consisted of three groups i.e. local community, policy makers and researchers or facilitators. Knowledge, perception and experiences from each group of stakeholders used to be called as LEK (Local Ecological Knowledge), PEK (Policy
Ecological Knowledge), and MEK (Modeler Ecological Knowledge). Meanwhile, the data
collection including spatial data, participatory landscape analysis, local and political
knowledge assessment about watershed ecology, data analysis related on hydrological
condition, and the stakeholders meeting constituted as a package of community awareness about watershed management at the study site.
In general, the perceptions on watershed hydrology among the three groups of stakeholders in Sumber Brantas Watershed (i.e. PEK, MEK and LEK) tend to be similar. The important hydrological issues in the Sumber Brantas Watershed are about flash-floods and drought, decrease of the number of springs in the watershed as well as their discharge, the decrease of water quality, and the more intensive soil loss due to erosion and landslide.
The three groups of stakeholders agreed that the discharge of main river (Upper Brantas River) depends on seasonal rainfall variability. During rainy seasons, the river discharge tends to be very high, while in dry seasons it dries up. The discharge ratio between rainy and dry season is high and tends to increase annually. The fluctuations of river discharge and the floods frequency is related to the percentage of forest area in the upstream. The above perception is supported by modelers (MEK) as indicated by the calculated discharge through simulation model under various scenarios of land cover areas. The amplitude of maximum and minimum discharges is affected by percentage of forest area in the watershed. Reduction of forest area in the watershed will increase the amplitude of maximum and minimum discharge. The simulation also shows extremely high discharges or flooding following heavy rainfall events.
LEK and PEK groups stated that the decreasing of the number of springs as well as the
discharge of the springs in the watershed was affected by deforestation. The deforestation will reduce the recharge area, so that the absence of forest will affect the discharge of the springs nearby. However, the MEK group mentioned that the most relevant recharge area of a spring is not necessarily adjacent to the spring, dependent to geologic and topographic conditions of the area. The three groups perceived that the decrease of the water quality in the watershed is mainly due to sedimentation and water pollution. Sediment in the river is mostly coming from erosion of agricultural and landslides on road-cuts, river-banks and steep lands. Pollutants in the main Brantas River is usually coming from the waste of human activity along the river, such as intensive agriculture, agriculture-based industry, and tourism activities. The agriculture-based industry along the Sumber Brantas watershed that produced pollutants are mushroom and flowers growers, intensive small-scale horticulture practices (fruits, vegetables, and flowers), and small-scale food and beverage industries. Meanwhile, the tourism activity includes hotel and restaurant business. The LEK group believed that the soil material transported into the river is mostly coming from the forest-production area that has been converted into agriculture lands by local farmers (known as pesanggem). Usually, they grow rain fed vegetables such as carrot, potato, cabbage in the steep slopes without proper management. The group also thought that the conversion of forest into agriculture land will trigger landslide evidence on the steep slopes. They were quite sure that the absence of tree vegetation on the steep lands was the major cause of landslides and flooding. Actually, the perception of the PEK and MEK group on the erosion and landslide issues are not quite
different from LEK group. However, they emphasized that slope is more prominent factor triggering landslides than the absence of trees.
Comparing the simulated discharge using the GenRiver model to the actual field measurement shows a poor relation. The measured discharge data collected by PJT 1 (Perum Jasa Tirta I) seems to have unexpected trends that cannot be explained well by the available supporting data such as rainfall data. However, the simulated discharge upon some landuse scenarios indicates some acceptable preferences compared to the actual field condition.
In conclusion, the similarity of perception among stakeholders in the watershed will give
chance to find the best management plan and practices in the near future. But there is still a problem to bring the stakeholders to sit together discussing their opinion, perception and hope on the future of the watershed. An appropriate system and mechanism of coordination and communication among stakeholders is certainly needed to build better understanding of the watershed. Environmental service mechanism can be potentially developed in Sumber Brantas watershed, since the early initiative has been explored and practiced by some stakeholders, such as Perum Jasa Tirta I. |
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