GEOPOTENTIAL CONSERVATION OF JIRAK RIVER BASIN AS A GUNUNG SEWU KARST CONSERVATION DEVELOPMENT MODEL AT SOUTH YOGYAKARTA

PROCEEDINGS JOINT CONVENTION BALI 2007
The 32^nd HAGI, The 36^th IAGI, and The 29^th IATMI Annual Conference and Exhibition

GEOPOTENTIAL CONSERVATION OF JIRAK RIVER BASIN AS A GUNUNG SEWU KARST CONSERVATION DEVELOPMENT MODEL AT SOUTH YOGYAKARTA

Srijono ¹⁾ , Dwikorita Karnawati ²⁾ , Kirbani Sri Brotopuspito ³⁾ ,
Bambang Hendro Sunarminto ⁴⁾ , Dulbahri ⁵⁾

¹⁾ Post Graduate Student, Dept. of Geography UGM, Yogyakarta 55281
sriy_geougm@yahoo.com
²⁾ Co-Promotor, Dept. of Engineering Geology UGM, Yogyakarta 55281
³⁾Co- Promotor, Dept. of Physic UGM, Yogyakarta 55281
⁴⁾ Co-Promotor, Dept. of Soil Science UGM, Yogyakarta 55281
⁵⁾ Promotor, Faculty of Geography UGM, Yogyakarta 55281

ABSTRACT

Jirak river basin is a part of Wonosari Basin physiography and Gunung Sewu Karst at South Yogyakarta. Drainage types of surface drainage change into subsurface drainage. Mining and residential development areas are indication of the area function changing. The research objectives are to identify, analyze, and submit geopotencial conservation recommendation.

Research method: geomorphology mapping, infiltration measuring, geopotencial identification, mining location, and measuring drainage water quality.

Jirak river basin divided in 2 geomorphology unit, are fluvial plain and plain – karst hills complex. The lithologies are member of Wonosari Formation, forming horizontal bedding to monocline, jointed and faulted. Lithology covered by mollisol, vertisol and inceptisol. Jirak river basin land use are for resident, agriculture and etc.

Infiltration rate average in jirak river basin 0.45 cm/min, yearly absorb coefficient 0.15, distributing water to subsurface river basin Bribin 170 l/sec. Content of Ca in the water supply is high, the impurity cause by limestone reactive and pollutant. Water chemical is polluted by pesticide, and tofu industry, detergent waste, and bacteria colli ≥ 2400, nitrite salt ≤ 0.03 mg/l, phosphate oxide 0.35 – 0.43 mg/l. Drainage water contain ferro oxide, cadmium (Cd), and Pb over the standard quality.

Land use changing function in fluvial plain the most distinctive is for ‘watu blirik’ mining, agriculture area shifting, increasing of run-off water, and decreasing of jirak river basin water quality. Mining wastes increase water impurity, with Ca²⁺ concentrate 59.1 mg/l.

Jirak river basin geopotencial conservation including limestone exploitation limitation with processing diversification, chemical substance using guidance in home industry, and also agriculture, water quality maintaining. Cave conservation from destruction caused by mining and pollutant. Forestry for jirak river basin infiltration area including Panggung Massive and Gunung Sewu physiography.

Keyword: water, river basin, Gunung Sewu, karst, conservation.