Analisis MRC untuk Karakterisasi Akuifer Karst di Mataair Mudal, Kabupaten Kuloprogo

Akuifer karst memiliki triple porosity yang membuat karakterisasinya sulit dilakukan. Tujuan dari penelitian ini adalah menganalisis komponen hidrograf banjir dan membuat Master Recession Curve (MRC) pada akuifer karst yang mengimbuh Mataair Mudal. Data yang digunakan adalah debit aliran dan curah hujan yang tercatat setiap 30 menit pada November 2017 hingga Mei 2018 (6 bulan). Hasil penelitian menunjukkan bahwa Mataair Mudal memiliki complex discharge regime dengan derajat karstifikasi pada kelas 5,5. Analisis komponen hidrograf banjir menguatkan hasil perhitungan derajat karstifikasi. Waktu menuju puncak banjir (Tlag) yang tergolong cepat (2,5 jam) menunjukkan telah adanya aliran conduit. Perhitungan waktu menuju aliran dasar (Tb) baik secara manual (hidrograf banjir) maupun automatis (MRC) memiliki rerata sekitar 40 jam yang mencerminkan bahwa akuifer karst yang mengimbunya masih baik dalam menyimpan airtanah. Secara keseluruhan, akuifer karst di Mataair Mudal masih didominasi oleh retakan bertipe diffuse, meskipun sudah memiliki retakan bertipe conduit yang cukup berkembangThe objective of this research was to analyze the nature of the flood hydrograph components and create a Master Recession Curve (MRC) to estimate the degree of karstification in Mudal Spring. Discharge and rainfall data were recorded every 30 minutes at time intervals between November 2017 and May 2018. The results show that Mudal Spring has a complex discharge regime with a karstification degree in the class of 5.5. Meanwhile, the time to peak flood (Tlag) which is relatively fast (2.5 hours) shows the existence of conduit flow in the flood event. Calculation of time to baseflow (Tb) has an average of 40 hours which reflects that the karst aquifer was still good in storing groundwater. Overall, karst aquifers in Mudal Spring are still dominated by diffuse type voids, although they already have conduit type voids that are quite developed.

Master Recession Curve (MRC) analysis to characterize karst aquifers of several springs in the north side of the Karangbolong (Gombong) karst area

Karst aquifers have triple porosity (diffuse, fissure, and conduit) which makes their characterization difficult, and often requires a combination of particular methods and investigation over a long period. The purpose of this study is to analyse the components of the flood hydrograph and create a master recession curve (MRC) in karst aquifers that recharge several springs on the north side of the Karangbolong Karst Area (Gombong). The springs studied include Kalisirah, Jumbleng, and Kalikarak springs. The data used are time-series discharges recorded every 15 minutes from November 2018 to March 2020. Furthermore, the reconstruction of the flow regime for MRC is carried out with the help of RC 4.0 software, which is at the same time able to define the level of karst aquifer development. The results showed that Kalisirah and Kalikarak Springs have a complex discharge regime with a degree of karstification in class 8, while Jumbleng Springs in class 5. Analysis of the components of the flood hydrograph reinforces the results of the calculation of the karstification degree. The time to the peak (Tlag) of the Kalisirah and Kalikarak Springs is relatively fast (1.94 and 1.44 hours), which indicates that conduit flow has developed, while Jumbleng spring has a longer Tlag of 2.69 hours. Calculation of time to base flow (Tb) both manually (by flood events analysis) and automatically (by MRC) shows that Kalikarak Springs has the longest time with an average of about 31 hours which reflects that karst aquifers which contribute to it are still quite good in storing groundwater, while Jumbleng spring has the fastest Tb value with an average of 17.25 hours which reflects the shortest release of water storage compared to the other two springs.

ANALISIS KURVA RESESI ALIRAN DASAR MENGGUNAKAN MODEL RESERVOIR LINIER RECESSION CURVE HYDROOFFICE PADA DAS WURYANTORO KABUPATEN WONOGIRI PROPINSI JAWA TENGAH

The hydrograph recession curve expresses the theoretical relationship between the aquifer structure and the flow of groundwater flowing into the river basin channel. These theoretical relationships are often empirically depicted using the base flow recession curve. The hydrograph recession curve is commonly used to estimate the recessionary parameters, aquifer properties and to evaluate alternative hydrological hypotheses. The river basin hydrograph recession curve records the behavior of the relationship between the aquifer structure and its association with groundwater outflow to the river channel. This research was conducted with the aim: to analyze the characteristics of the baseflow recession based on the parameters and coefficients of the recession, and the shape of the individual recession curve and the master recession curve. The characteristics of the baseflow recession to research sub-watershed have the recession curves tend to sloped, describing the water storage well enough. The parameter Q0 (recession early), α and the recession constant Krb ranging from 0,80 – 0,90 for the individual and master recession curve in all three research sub-watershed. This calculation result indicates that the recession characteristics in three research sub-watershed have the condition of water storage is excellent, because they are supported by the aquifer characteristics dominated by the geological structures are more permeable (porous).