Academic journal article The Indonesian Journal of Geography

Water Quality Characteristics of Jonge Telaga (Doline Pond) as Water Resources for the People of Semanu District Gunungkidul Regency

Academic journal article The Indonesian Journal of Geography

Water Quality Characteristics of Jonge Telaga (Doline Pond) as Water Resources for the People of Semanu District Gunungkidul Regency

Article excerpt

1. Introduction

Karst area is a landscape characterized by a unique hydrology. It makes karst a complex aquifer due to secondary porosity development, forming a more developed subsurface drainage and, hence, a rare surface drainage [Ford and Williams, 2007]. Because of the deeply located groundwater (underground river), water resources in karst areas are hardly accessible.

Doline is a karstic landform, of which the shape is a closed round or oval depression with a size of several meters to about one kilometer [Ford and Williams, 2007]. Sweeting [1972] categorized doline as a medium-sized landform. According to karst literature, it is often referred to by various terms: sinkhole, sink, swallow hole, cenote, and blue hole [Haryono and Adji, 2004]. Every doline or closed depression is composed of three components [White, 1988], namely a drain, which is a channel with high permeability that drains water from doline into the underground system, a solutionally altered zone below the bedrock surface, and a soil cover, colluvium, glacial deposit, volcanic ash or other loose material. However, surface material is not evenly distributed in every part of doline. A temporarily or perennially rainwaterfilled doline is termed telaga (doline pond). Aside from the influence of external factors such as evapotranspiration, the capacity or volume of a doline pond is controlled by its characteristics.

Because of the concomitant drought events or water issues of a karst area, water resource becomes a pressing issue in Gunung Sewu karst area. Most of the local people have no access to clean water. Therefore, doline ponds used to support 90% of water supply in the area especially before the 1990s when water supply infrastructure had not been constructed [Haryono et al, 2009]. Nowadays, many doline ponds turned dry. Only 30% of all doline ponds in Gunung Sewu remain providing water throughout the year. In some parts of the area, local people are forced to fetch water from springs or doline ponds because the groundwater (underground river) is found at a depth of more than 100 masl and, therefore, difficult to access.

Gunungkidul, one of the regencies of the Special Region of Yogyakarta, is notorious for its water scarcity during dry seasons, especially in the karst area. In addition to groundwater (underground river) and spring, water resource used to fulfill the needs of the local people is doline pond. According to Haryono et al. [2009], there are 443 doline ponds scattered throughout Gunung Sewu karst area, 282 of which are located in several districts in Gunungkidul. The districts are Purwosari, Panggang, Saptosari, Playen, Paliyan, Tanjungsari, Tepus, Girisubo, Rongkop, Semanu, and Ponjong.

Various existing problems in doline ponds include decreasing water storage, water loss, and degrading water quality. Aside from natural factors, the behavior of people around them also takes part in the emergence of these problems. In this case, the role of institutions becomes an integral part of doline pond management. The water storage of doline ponds decreases due to rapid sedimentation and infiltration rate. In addition, it may disappear due to bed sediment leak, caused by soil cover removal during lake deepening and construction building around them, and high evaporation rate. Meanwhile, water quality degradation is caused by a variety of activities within the doline ponds, such as bathing (humans and domestic animals) and washing, which introduce pollutants into the water. In addition, the surrounding land use may affect the water quality, particularly in relation to both organic and inorganic fertilizers.

An input of continuous pollution load may exceed the natural capacities of doline ponds to accommodate pollution loads that lead to water quality degradation. Even though doline ponds are hydrologically different from lakes or reservoirs, which have a real water circulation due to the presence of inlet and outlet, the assessment of their pollution load capacities uses the slightly modified principles of the same assessment for lakes or reservoirs. …

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