| dc.description.abstract | One of the most important issues in watershed management is the use of land, especially in the upstream catchment area. People effort to fulfill their ends meet can cause land conversion. As a result of the land conversion, the Cisadane River condition seems quite apprehensive in the last two decades. Environmental degradation in Cisadane watershed in both the upstream and downstream has a heavy impact to the availability of water resources in Cisadane River. In relation to this fact, an in-depth study on land use change in Upstream Cisadane Watersheds and its dynamics need to be conducted. Particularly, the impact of land use change on water yield. This research purpose is to forecast the future of land use changes (using CLUE-S) and assess the impact of the predicted land use changes on water yield in Upstream Cisadane Watershed (using HEC-HMS). This research was conducted in Upstream Cisadane Watershed – Bogor. The study area is Upstream Cisadane Watershed with outlet of watershed in Empang, which located in both Bogor Regency and Bogor Municipality. Geographically, it is located between 6036’26.05” – 6047’08.49” South Latitude and 106044’30.27” – 106056’36.76” east longitude. Four scenarios are developed based on land use demand (population growth) and area restriction (spatial policy). The scenarios presented are not necessary the most realistic, but are made in such a way that they provide information on the functioning of the model. Binomial logistic regression is used to examine the relation between land use and possible driving factor. The result of this analysis are coefficient values that shows the contribution of each driving factor to land use change. ROC (Relative Operating Characteristics) is a method to measure the goodness of the statistical model. The probability of each land use resulted from logistic regression is compared to the real land use map to calculate the equal category of each grid cell between those maps. This method will depict the capability of regression equation to represent land use characteristics. The goodness of the statistical measurement revealed that ROC values for urban water area, grassland area, estate area, settlement area and forest area were 0.903, 0.701, 0.780, 0.813 and 0.994, which indicated that the probability of land uses built from these models were capable to represent land use changes and empirical analysis by using logistic regression method was satisfactory to examine the relationship between driving factors and land use change in study area. Through model validation process shows that overall accuracy and Kappa accuracy for land use simulation are 90.83 % and 86.00 % or categorized as fit. It indicates that the driving factors have a good capability to explain land use pattern in study area and it can be used to predict future land use pattern. According to the change detection for the land use classification year 1991, simulated year 2000, year 2010, year 2020 and year 2030, it can be seen that settlement, forest and grassland area are increasing over time, whereas estate tend to decrease and water remains constant. Based on the findings, settlement area were significantly increase during the period 1991-2009 and causing the pressures in the study area. Developing a model basin is an important step to assess the impact of land use changes on water yield in Upstream Cisadane Watershed using HEC-HMS. A configuration needs to be developed in the model basin to describe physical representation of a watershed based on its hydrology elements. In this research, there are seven hydrology elements available in HEC-HMS; Sub-basin, Reach, Reservoir, Junction, Diversion, Source, and Sink. The research employs 19 sub-basins, 9 reach, 9 junctions, and 1 outlet. Developing a model basin also includes calculation in 4 main sub-models, i.e.: loss model, transform model, base flow model, and routing model. The model calibration done by adjusting the initial abstraction, curve number and impervious area values, until the results matched the field data. The process was completed manually by repeatedly adjusting the parameters, computing, and inspecting the goodness of fit between the computed and observed hydrographs. During calibration process by using half-year daily data (February 1, 2010 – July 31, 2010), the accuracy achieved 0.524 of R2. Performance of the model was objectively evaluated by using Nash-Sutcliffe Efficiency (NSE) and Relative Volume Error (RVE), in which it gave good efficiency value (NSE) of 0.67 and 42.9 % of RVE. By using three tests it can be stated that the model is satisfactory accepted. Four hydrographs were simulated by using the same parameters in which was used during calibration and validation model. In this research, again the rainfall data of 2010 (February 1, 2010 – July 31, 2010 Period) was used as meteorological input. All these four scenarios were run using same parameters, except the curve numbers, percent impervious and initial abstraction are based on those previous land use condition. The simulated hydrograph obtain the peak flow and water yield information for four different land use scenarios. The values of each scenario peak flow are 81.00 m3/s, 81.10 m3/s, 81.00 and 81.10 m3/s for scenario 1, scenario 2, scenario 3 and scenario 4 respectively. While the value of water yield are 276,085.00 m3, 278,038.90 m3, 275,143.20 m3 and 279,178.20 m3 (all values for water yield are multiplied by 1000), for scenario 1, scenario 2, scenario 3 and scenario 4 respectively. Based on the comparison about values of water yield between scenario-based simulation for Year 2030 and existing condition of Year 2010 data shows increasing of water yield from Year 2010 to Year 2030. The increasing values of water yield influenced by forest rehabilitation activity by the government inside forest area and the development of community forest outside the forest area. Increasing values of water yield is quite high for scenario 2 and scenario 4, where government policy about restriction of land use inside forest area applied. That means government policy to prohibit land use conversion inside forest is appropriate to apply. | en |
