| Flood Risk Reduction Capital Town With Development Channel |
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Flood Risk Reduction DAM Capital Development Trenches With the Ciliwung Upper Watershed Sawiyo High rainfall that occurs in a short time cause the ratio terintersepsi water plants, soil terinviltrasi not worth the run-off. This is exacerbated when a long rain events, so almost all the rainfall will be transferred into the flow because the soil surface in a state already saturated from previous rain (Sawiyo et al., 2007).
Flood and puddles in the downstream area of recent increasing both the intensity and frequency due to damage both watersheds in the upstream, middle and downstream. DAS damage caused more by a change in land use due to competition of interests. Changes in land use in watershed Upper Ciliwung cause an increase in 100-year flood flow DAS m3/dt Ciliwung from 370 in 1973 to 570 m3/dt in 2000. Watershed management efforts vegetatively with various types of land uses, such as forests and fields followed by a garden with shady trees, show a hydrological functions better than other types of uses such as fields and fields. Because more and more changes in forests and fields into the fields and housing greater the rain cutah transferred into surface streams. Material and economic losses from floods have also tended to increase. Floods in Jakarta in 2002 for 2 weeks caused economic losses 5-6,7 trillion Rupiah. Nationally, the agricultural sector the average area of paddy crops damaged by flood disaster reaches 100 thousand hectares were from drought reaches 200 thousand hectares per year. Harvest Technique rain and surface flow Rain harvesting is a technique to harvest / hold / block rain falling and the surface flow into a media / container for Indirect water wasted. Rain harvesting techniques and surface flow can be divided into 2 of the vegetative and civil engineering diilustrasukan in Figure 1.  Figure 1. Rain harvesting systems and the flow of surface Dam Dyke Dam is one of the moat building technique to block the water harvesting and rainwater and surface flow with a certain volume in a flow path of a ditch or creek. Building dams can be constructed trench multilevel (cascade series) from upstream to downstream, so the impact on the reduction intaensitas volume and extensive flooding and irrigation services increased. Trench dam construction schemes gradually presented in Figure 2. Benefits can ditch dams, among others: (a) may reduce the risk of flooding, thus reducing the risk of erosion / sedimentation in downstream areas, (b) may reduce the risk of drought and increased irrigation area due to an increase in water reserves (stock water) according to the scale space and time, (c) of supplemental irrigation can create a diversification of crops cultivated and ultimately improve land productivity and farmers' income (d) provision of water for household purposes, (Balitklimat, 2007).  Figure 2. Illustration trench dams functioning gradually reduce the volume of peak flow, increase response time and increase soil water reserves. Model development ditch dams Design development trench dams done by considering elements of the position, dimensions / capacity and the capacity in a number of sub-watershed areas or watersheds. Based on research in 2005-2008 was the trench dams can reduce flooding and drought ntensitas significant, so the technology is feasible to be developed in a watershed pegelolaan system. The position of the trench dams In determining the criteria for the position of the trench dams need to identify factors that influence the feasibility, the level of interest and weighting and scoring system of all the elements assessed. The value (skore) is determined based on the level of importance of an element in determining the feasibility of the dam trench positions. The sum value of scoring and then will determine whether or not a point worthy of such dams built trenches. Elements that determine the feasibility of a point in the flow path of the trench can be constructed dams are presented in Table 1 and Level credentials presented in Table 2. Volume and number of dams trench Criteria for determining the model volume / capacity of the dam capacity that can be built trenches in a watershed area defined by the difference in peak flow with the safe flow (which does not cause flooding in downstream areas). For Ciliwung Upper Basin dam volume is determined based on the difference ditch summit with debit debit standby at 3 in the amount of Katulampa weir 380 m3/dt. Debit is the lowest limit that can cause flooding in the downstream (Jakarta) due to transfers of water from the watershed Upper Ciliwung. It is expected the development of dam building trenches and other facilities in the watershed with volume Ciliwung can avoid flooding on the banks of the river and more flooding in the downstream area (Jakarta). Table 1. Feasibility level element in determining the model parameters Dyke Dam Positioning |
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