Urgency of Conservation of Gunung Sewu Groundwater Sources
By : Ronald Eberhard
Usually people get water from a fertile area, but can you imagine there is a way to get water from a source that not located in a fertile area. The meaning of infertile area in this context is karsts area. There are many karsts area, but one in Gunung Sewu is interesting. The interest point of Gunung Sewu, the name was taken from Javanese language translated as “Thousand Hills”, is the relief of the area is dominated many times by that number of remarkably similar, small conical hills. Each hill is around 50m high and 300m in diameter. The result is a distinctive but chaotic landscape lacking an integrated active valley network.
Gunung Sewu is a range of hills covering about 800 square kilometers, adjacent to the south coast of Central Java. The area lies immediately south of the small town of Wonosari and about 50km southeast of the city of Yogyakarta. The hills form a unit elongated east-west, with along the central crest line mostly around 250-300m but rising to over 500m to the northeast. To the south the hills drop steeply to the coast, while to the north they fall to the plain of the Wonosari Plateau at an elevation around 175 m. The conical hills developed in strong reed lime stones are the natural product of a long period of tropical karsts erosion, and Gunung Sewu does in fact constitute one of the world’s finest example of cone karsts.
The unique point about Gunung Sewu that related to water resources is the complete replacement of any surface drainage systems by an integrated under drainage system. Surface water in the area is confined to short stream out active only in the wet season and feeding into sinkholes, or pounded depression locally known as “telaga”, which develop where drainage is impeded by thick valley clays and the lack of an adequate sinkhole. Cave entrances abound, and there are hundreds of open sinkholes, in the floors almost every depression between the small conical hills. The underground watercourses coalesce and mostly feed to springs along the south coast. Within Gunung Sewu itself, the groundwater drainage is typical of that of mature karsts in that the great majority of the flow is through discrete, widely-spaced conduits, or caves, and most water drains rapidly downwards through the lime stone to a deep and gently graded water table. These two factors combine to make the economic exploitation of the groundwater in Gunung Sewu very difficult.
Nowadays groundwater is not stand anymore as a free commodity but developed into an economic commodity that has an important role even in some places has become more strategic. To optimize groundwater exploitation there is a guide in planning groundwater exploitation. The plan including the stock taking of groundwater potential, exploitation planning, permission, checking and controlling, also groundwater conservation. The stock taking of groundwater potential is consider as the most determining in groundwater exploitation that environment based because of the availability and the potential of groundwater in area is determined by natural factor. The first step in the stock taking of groundwater potential is stock taking all the aspect of groundwater to know its potential through mapping activity, investigating, research, exploration and evaluation, collecting and managing groundwater data. The stock taking activities above done through collecting, evaluating and analyzing data to get :
Information of groundwater basin limit
Information of dimension, geometric and aquifer parameter
Information on supplement area and groundwater dismissal area
Information of groundwater debit
Information of groundwater quality
Information on the debit groundwater exploiting
The second step is groundwater exploitation planning. To fulfill a demand groundwater exploitation must consider :
Groundwater need for long term based on the groundwater exploitation development plan that exist and the future development plan for groundwater exploitation
Invention (mathematic simulation model) of hydro geologic condition that similar to natural condition
Groundwater exploitation planning in a certain time that fits the safe quota of groundwater exploitation so that the exploitation doesn’t cause negative effects
Groundwater exploitation to fulfill demand must less or maximally even with the natural supportability
Locations that have a critical condition of groundwater environment will have its own exploitation regulation and the further exploitation must fit its natural supportability. For the establish one obligated to minimize exploitation debit
The third step is permission. Water resource or groundwater drilling can be done after get drilling permission and groundwater exploitation permission with rules below :
The allocation of groundwater exploitation for drinkable and household water is the main priority above other needs
Groundwater exploitation on free aquifer, the first priority is for drinkable and household water
Groundwater exploitation for other needs will not disturb the household needs
In managing, exploitation based on allocation priority rules and also concern about civil needs and local condition
The permission is act as a form of legal aspect.
The fourth step is checking and controlling. The successes of groundwater exploitation that environment based is determined on checking and controlling functions so that the continuity of groundwater exploitation can take place.
The first part is :
Checking
Checking activity involves :
Checking the operation of technique requisite that listed in the groundwater exploitation permission
Checking for the operation of environment analysis
Checking for the possibility of the pollution of groundwater environment
Controlling
Controlling activity involves :
Monitoring activity that are :
The monitoring of groundwater debit and quality
The monitoring of environment effect because groundwater exploitation
The monitoring in the changing of ground function and exploitation
Production of groundwater exploitation controlling map that include determining :
Groundwater zoning (safe, affected, critical and damaged)
Aquifer deep that safe for exploitation
Groundwater exploitation debit quota based on the supportability potent
Groundwater exploitation debit based on allocation
Giving administrative sanction and law sanction based on the rules and constitution that valid concerning drilling operator and or groundwater consumer if there any damage in the environment because groundwater exploitation
The last step is groundwater conservation. Groundwater conservation is groundwater management to guarantee the exploitation wisely and guarantee the debit with constantly keeping and optimizing its quality. In brief, this is a needed act in groundwater resource using so that that the exploitation will be optimal and continuously without creating negative effects on the condition and the environment of groundwater resources.
Technique efforts that can be done in groundwater conservation operation is involving :
Maximizing the groundwater supplementation
Regulating the groundwater using
Groundwater protection
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