Land cover change impact on urban flood modeling (case study: Upper Citarum watershed)

The upper Citarum River watershed utilizes remote sensing technology in Geographic Information System to provide information on land coverage by interpretation of objects in the image. Rivers that pass through urban areas will cause flooding problems causing disadvantages, and it disrupts community activities in the urban area. Increased development in a city is related to an increase in the number of population growth that added by increasing quality and quantity of life necessities. Improved urban lifestyle changes have an impact on land cover. The impact in over time will be difficult to control. This study aims to analyze the condition of flooding in urban areas caused by upper Citarum watershed land-use change in 2001 with the land cover change in 2010. This modeling analyzes with the help of HEC-RAS to describe flooded inundation urban areas. Land cover change in upper Citarum watershed is not very significant; it based on the results of data processing of land cover has the difference of area that changed is not enormous. Land cover changes for the floods increased dramatically to a flow coefficient for 2001 is 0.65 and in 2010 at 0.69. In 2001, the inundation area about 105,468 hectares and it were about 92,289 hectares in 2010.


Introduction
Land cover change is dynamic process-taking place on the biophysical surfaces that have taken over a period and space is of enormous importance in natural resource studies. Land cover change dynamics are substantial elements for monitoring, evaluating, protecting and planning for earth resources. Land cover changes are the major issues and challenges for the eco-friendly and sustainable development for the economic growth of any area.
Land cover change is the conversion of open area to area woke indicated it would decrease catchment areas. Nowadays, the efforts to tackle the incident are still conventional runoff to flow quickly into the body of the river flow through the efforts of normalization techniques. Such shunt and water bodies [1]. Social and economic development drives land use and land cover changes, which have potentially enormous impacts on water resources. Changes in land use and land cover affect the partitioning of precipitation through the vegetation and soil into the main water balance components of interception, infiltration, evapotranspiration; surface runoff and groundwater recharge [2]. Land cover is an important determinant of Eco hydrologic processes in watershed systems. Continued urbanization changes the very nature of Eco hydrological regimes of watersheds and increases their vulnerability to flooding, soil loss, and water pollution [3]. The catchment hydrologic response suspects of having multiple impacts on urbanization and population concentration. The impact of land cover originates from a multiplicity of landscape modifications. This modification may potentially lead to compensations and makes it difficult to synthesize the results from the numerous case studies related to the impact of urbanization on catchments hydrologic response. In some cases, the observed data are not in full agreement with the ideas that urbanization tends to increase flood occurrence and intensity while decreasing base flow [4]. The researcher challenges of assessing the impacts of future climate change are enormous. The institutional involved in using that science for making policy are arguably even greater. The development of region has highlighted the difficulties of reconciling. The supply of climate science with the demand for research is more useful, and the policy makers used it [5].
Flood in an urban area can affect all activity in that place; in the long term, it occurs because of land cover change. This study is a modeling and investigates the effect of land use change on the urban flood in the upper Citarum Watershed using a physically based hydrological simulation model. The objective of this paper is to compare the flow changes and flood inundation area detected by a conceptual modeling approach (the residual approach) on the particular case of urbanized catchments. Urban flood modeling is the land cover change for the years 2001 and 2010 in upper Citarum watershed. Comparative analysis of this two term and conditions between 2001 and 2010 inform some conclusions about the tensions between adaptive and risk-based approaches. The role of institutional is risk in adaptation, and the importance of institutional dynamics in shaping the framing climate uncertainties and policy response to scientific knowledge.

Study Area
Upper Citarum watershed flows through the South of Bandung Regency up to Saguling Reservoir. The upper Citarum watershed spread geographically at 6°43'21.8 "-7°19'38.1" South Latitude and 107°32'2 "-107°53'51.6" East Longitude.  Upper Citarum watershed administratively passes several cities and districts, such as Regency Bandung, Sumedang, Bandung, and Cimahi. Upper Citarum watershed defined as one area that serves to accommodate, store and drain the water upstream of Saguling Reservoir (Curug Jompong) with a total area is 1.771 square kilometers.

Data Sources
The image data products used in this study are land cover data for the years 2001and 2010. In this study, the rainfall data used is the record data from 2001 to 2010. The data of rainfall sourced from the data of Major River Basin Organization of Citarum, Ministry of Public Works. The data of debit recording in this research obtained from Research Centre and Development of Water Resources, Ministry of Public Works. The data of the discharge serves as the calibration and verification reference of the modeling created. The available record data is the measurement data of water level three times a day. Upper Citarum watershed utilizes remote sensing technology to provide information on land coverage by interpretation of objects in the image. The information obtained to show areas that have the most critical and most sensitive land capability.

Land Cover Modeling
Land cover change is dynamic process-taking place on the biophysical surfaces that have taken over a period and space is of enormous importance in natural resource studies. The data processing of the land cover and its classification system uses the help the geographic information data. Based on the data obtained there is ten classifications of land cover that will be determined the area of each for years 2001 and 2010. Then the data will be compared the amount of change from 2001 to 2010 into the form of bar charts [6].

Flood Modeling
Forest cover changes can have a great impact on hydrological characteristics of a watershed. Flood discharge can increase as result of a change in land use. Flood peak flow may increase after trees cut down [7]. A simple modeling framework provided based on accessible input data and a freely available and widely used hydrological model (HEC-RAS) to check the possible effect of LULC changes at a particular sub-catchment on the hydrograph at the basin outlet [8].
In this flood modeling, the first analysis of rainfall design and flood discharge design with return period are 5-year, 10 HEC-RAS is a widely used hydraulic software tool developed by the U.S Army Corps of Engineers, which combined with the HEC-HMS platform for hydrological simulations. HEC-RAS employs 1d flood routing in both steady and unsteady flow conditions by applying an implicit-forward finite difference scheme between sequent sections of flexible geometry. In all the above models, two boundary conditions required, which usually set at the upstream end of the channel through an imposed inflow as well as the assumption of uniform water depths at the upstream and downstream end (kinematic wave condition). Although an imposed depth would result in more stable solutions than the uniform flow, we choose the latter since, in practice, it is rare to know the temporal evolution of the water depth at a particular location. The models compute the appropriate time step based on the Courant number stability criteria [9].
This method applied the Hydrologic Engineering Center River Analysis System (HEC-RAS) model to estimate the potential catastrophes for different peak outflow scenarios with conclusions and recommendations [10]. After incorporating resampling and vertical errors, all resampled raster datasets used to create a 1D HEC-RAS model. HEC-RAS is the most commonly used flood model tool in Indonesia. The HEC-RAS parameters kept unchanged for different DEMs because the goal is to investigate the sensitivity of inundation maps to topographic errors instead of trying to create newly calibrated model for each topographic dataset [11].

Calibration and Validation Method
The method compares the observed discharge, and then analyzed the parameters that influence the modeling results. Optimum parameter values in calibration found by statistical measures. The result of comparison then determined the strength in predicting the modeling by Nash-Sutcliffe model of efficiency coefficient (E). The Nash-Sutcliffe efficiency (NI) is the two criteria most widely used for calibration and evaluation of hydrological models with observed data [12]. Nash-Sutcliffe Index can range from -∞ to 1. The value of 1 (NI=1) corresponds to a perfect match of modeled discharge to the observed data. The value of 0 (NI = 0) indicates that the model predictions are as accurate as the mean of the observed data, whereas it is less than 0; it occurs when the observed is the better predictor than the model [13]. The verification process based on the observation flow verified parameter is the runoff.

Calibration and Validation Modeling
The calibrated HEC-HMS model applied for the land cover scenarios to assess the potential land cover impacts on the Snyder and SCS synthesized hydrographs obtained based on the parameters input into the upper Citarum watershed, they analyzed for calibration and verification. The rain that occurs is the total daily rain that distributed evenly in the watershed. Calibration and verification of Citarum watershed carried out at each of the maximum floods in the study sites for three years i.e. 2007, 2008 and 2010, with calibration results as shown below.

Conclusions
This study and have shown that land cover change in upper Citarum watershed is not very significant. It based on the results of data processing of land cover has the difference of area that changed is not enormous. it increased dramatically to a