ANALYSIS OF KREO SUB WATERSHED

IN SEMARANG BASED ON REMOTE SENSING

AND GEOGRAPHIC INFORMATION SYSTEMS

1. Image Interpretation

Kreo Sub Watershed administratively located in Semarang District, Kendal District and Semarang City. Astronomically it located in 110⁰ 18’ 30’’ -  110⁰ 22’ 45’’ East Longitude and 7⁰ 1’ 15’’ - 7⁰ 11’ 15’’ South Latitude. Kreo Sub Watershed extend from north to south at Ungaran Mountain north slope.

Kreo Sub Watershed image aqcuired from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data. ASTER data is an imaging instrument onboard Terra, the flagship satellite of NASA's Earth Observing System (EOS) launched in December 1999. ASTER is a cooperative effort between NASA, Japan's Ministry of Economy, Trade and Industry (METI), and Japan Space Systems. ASTER is used to create detailed maps of land surface temperature, reflectance, and elevation (NASA, 2004).

ASTER image of Kreo Sub Watershed were classifying in maximum likelihood classification method. Maximum likelihood considers both the variances and covariance of the class signatures when assigning each cell to one of the classes represented in the signature file (Horning, etc, 2010). With the assumption that the distribution of a class sample is normal, a class can be characterized by the mean vector and the covariance matrix. Given these two characteristics for each cell value, the statistical probability is computed for each class to determine the membership of the cells to the class. Output results processed in cosmetic operation (Fig.1 and Fig. 2).

Fig. 1. Land Cover of Kreo Sub Watershed

 

Fig. 2. Land Type of Kreo Sub Watershed

Based on Fig.1 about land cover of Kreo Sub Watershed, it can be seen that in Upstream Area, there are smal area of high density vegetation. Downstream Area was full of building area and lesser in Middle. Land cover of Kreo Sub Watershed was incompatible for ideal watershed. High increasing in population make uncomfortable condition in Kreo sub watershed.

On Fig. 2 it’s about land type, Andosols usually found in surrounding volcano mountain cone and high slope. Latosol mostly come from volcano material, intrusive igneous rocks. It found in wet climate, elevation between 300-1000 meters. Mediteran found in slope under 400 meters, mostly fom limestone and volcano materials.

2. Area Profile

				Vegatation Density
	More						Less
				Building Area

 

Less

More

                                                  

Fig. 3. Profile of Kreo Sub Watershed

3. Short Description for Development and Disaster

Kreo Sub Watershed is a part of Garang Watershed. There are Kreo, Kripik and Garang River which flow became one through Garang River to single outlet. In context of development and disaster, it’s comphrensive effort to view Kreo Sub Watershed as a part of Garang Watershed which affect each others.

Fig. 4. Drainage Pattern of Garang Watershed

Shape of Garang Watershed (Fig 4) like bottle, which bulge in under part and tighten in neck. In Fig 3. Shown that this watershed have high steep slope. Bottle shape have consequence, if there is high intensity of rainfall (input) that accumulate, run off will have high speed and less time to reach the downstream area. And Infiltration area in upstream decrease each day because of land opening so there is flood disaster in Semarang City. In case of Kreo Sub Watershed, which have extended shape, debit was small relative, it make time to reach downstream slower than in bottleneck shape. Infiltration capacity in Kreo Sub Watershed highest in forest land use, mixed garden and paddy field (Setyowati, 2007). Infiltration capacity in forest area is highest than the other because of coarse land texture and roots of vegetation which deep penetrate through land and make pores, so water from rainfall easier to infiltrate. But forest condition in Kreo sub watershed worse each year (Raharjo, 2009). Nugraha and Cahyadi (2012) analyze that Garang Sub Watershed was the first priority in case of flood mitigation, followed by Kreo and Kripik Sub Watershed. Kreo Sub Watershed also have potential for flood, it must be concern of all stakeholder in Kreo area in their development plans.

In a development issue, there are distribution in Kendal and Semarang Government. Cooperation between of them needs to be held, forest agency, non-government organization, private organization or anything else which related to watershed development must coordinated. Sometimes there is crash between economic or human right necesity and conservation. Conservation wants to make “green” everything and not to disturbance the balance watershed ecosystem especially in upstream area. In the other hand, human need living area, food source, etc which cause land use change. Use of remote sesnsing and geographic information system in development issue can be improve the master plans of development especially in Kreo Sub Watershed. It can be analyze, forecasting, simulating what the effect of developments in present so we can prevent the hazard or disaster.

REFERENCE

Horning, N., etc. 2010. Remote Sensing for Ecology and Conservation. New York: Oxford University Press.

NASA. 2004. Advanced Spaceborne Thermal Emision and Reflection Radiometer. Acessed from http://asterweb.jpl.nasa.gov/ at November 29^th, 2012.

Nugraha, H., & Cahyadi, A. 2012. Analisis Morfometri Menggunakan Sistem Informasi Geografis Untuk Penentuan Sub DAS Prioritas (Studi Kasus Mitigasi Bencana Banjir Bandang di DAS Garang Jawa Tengah). Conveyed on National Conference of Informatics 2012 UPN Veteran. Yogyakarta, June 30^th, 2012.

Raharjo, P., D. 2009. Perubahan Penggunaan Lahan DAS Kreo Terhadap Debit Puncak Dengan Aplikasi Penginderaan Jauh. Jurnal Riset Geologi dan Pertambangan. Jilid 19 No. 2. 69-84

Setyowati, D., L. 2007. Sifat Fisik Tanah dan Kemampuan Tanah Meresapkan Air Pada Lahan Hutan, Sawah, dan Permukiman. Jurnal Geografi. Volume 4 No. 2