Various surveys and studies have shown that the condition of water resources in Java and Bali is critical. The calculation of the of water balance in the dry season in 2003 and prediction for the year 2020 shows that the island of Java and Bali in 2003 is experiencing water deficit amounting to 13.1 billion m3. In 2020, the deficit will increase significantly to 18.8 billion m3. The index of water availability on the island of Java and Bali, where 60% population of the Indonesian live, according to a survey in 1986 amounting to 1,750 m3/person/year, is critical according to the classification of World Water Resources Institute.
The assessment of forests’ hydrological role to the continuity of the flow needs to be proven scientifically. Basic flow is one important indicator of the water resources condition in the dry season. "On the other hand, the study on the controversy of vegetation influence on the groundwater supplies need to be done to formulate the contribution of the forestry sector to anticipate water resources crisis," said Muchamad Saparis Soedarjanto, S.Si., M.T, in his doctoral open examination of Geography science at the Auditorium of UGM’s Faculty of Mathematics and Natural Sciences on Saturday (20/8). On that occasion, Soedarjanto defended his dissertation entitled 'Spatial co-variation on the relation of Vegetation Closure with Basic Flow Recession on the island of Bali'.
Spatial co-variation is an expression of geomorphology paradigm in geography, which also discusses the phenomenon of the landscape. Basic flow is one component of landscapes. In his research, Soedarjanto is trying to assess the influence of the vegetation density and its relation to the other physical aspects of the Watershed (DAS) against the base flow recession coefficient. "The research was conducted in Bali by including 30 watersheds. The implementation has three stages, namely field data measurement, data gathering from relevant agencies and data analysis," the man born in Surakarta, May 12, 1968, added.
Soedarjanto said the research is limited to the influence of the vegetation density and its relation to the other physical aspects of watersheds against base flow recession coefficient. Thus, hydrological role of vegetation in relation to its effects on ground water storage that is represented by the flow base can be studied; the influence of vegetation canopy closure toward the characteristics of watersheds basic flow is assessed as well as to find the relation with morphometry aspects, rock and soil types; and to find the spatial co-variation of basic flow in the watersheds that have various characteristics in terms of vegetation closure, morphometry, type of rock and soil.
The conclusions of Soedarjanto’s study on 30 watersheds on the island of Bali which is a tropical monsoon region and has major material in the form of volcanic quart are: first, the higher the density of vegetation canopy, the higher the absorption of ground water, thus the more powerful is the role of vegetation as a pump system in the transformation of groundwater into water vapor through transpiration mechanism.
Second, the dual role of vegetation toward the basic flow is combinative and related to other field factors, such as the drainage density and soil infiltration capacity. Third, the canopy density and rock type are the controlling factor in determining the spatial co-variation of basic flow on the island of Bali through cluster analysis of hierarchy and non-hierarchy methods. "The low value of base flow recession coefficient is found in watersheds with a low canopy density and composed of rocks with high permeability, i.e. tefra and alluvium," Soedarjanto who had served as Head Section of Watershed Evaluation, Watershed BP Unda Anyar in Denpasar, Bali, explained.
After defending his dissertation in front of the examiner team, namely, Prof. Dr. Suratman, M.Sc., Prof. Dr.rer.nat. Junun Sartohadi, M.Sc., Dr. M. Pramono Hadi, M.Sc., Drs. Projo Danoedoro, M.Sc., Ph.D., Prof. Dr. Sudarmadji, M.Eng.Sc., Prof. Dr. Sutikno, Dr. Senawi, M.P., and Dr. Ir. Harry Santoso, Soedarjanto is eventually declared to graduate cum laude and became the 1444th doctorate degree holder from UGM.