Kajian Potensi Intrusi Air Laut ke dalam Akuifer di Wilayah Pesisir Glagah Kabupaten Kulonprogo Daerah Istimewa Yogyakarta

KIESHA ARUNDYA S, Dr. Langgeng Wahyu Santosa, M.Si.

2023 | Skripsi | S1 GEOGRAFI LINGKUNGAN

Penurapan airtanah yang berlebihan akan menimbulkan gangguan keseimbangan pada interface yang mendorong terjadinya penyusupan air laut ke airtanah atau intrusi air laut. Air laut yang bercampur dengan airtanah akan menyebabkan penurunan kualitas air sumur, sehingga air menjadi tak layak untuk digunakan. Penelitian ini bertujuan untuk mengkaji dan menganalisis potensi intrusi air laut ke dalam akuifer di wilayah pesisir Glagah, Kecamatan Temon, Kabupaten Kulonprogo, dengan pendekatan analisis: pola aliran airtanah bebas (flownet); karakteristik akuifer berdasarkan rekonstruksi hidrostratigrafi; karakteristik airtanah berdasarkan hidrokimia airtanah bebas di daerah penelitian; dan menganalisis potensi intrusi air laut di daerah kajian ditinjau dari ketiga metode tersebut. Pengambilan dan pengukuran data ketinggian muka airtanah (TMA) dan nilai daya hantar listrik (DHL) dilakukan dengan sensus, sedangkan untuk pengambilan sampel airtanah bebas dilakukan dengan purposive sampling. Analisis data pola dan arah aliran airtanah bebas menggunakan interpolasi linear. Rekonstruksi hidrostratigrafi berdasarkan pendugaan geolistrik diperoleh dari data sekunder dalam Santosa (2010). Data kandungan ion mayor sampel airtanah diperoleh dari analisis laboratorium kemudian dihitung Charge Balance Erorr (CBE) untuk menguji kualitas sampel. Analisis hidrokimia airtanah dilakukan berdasarkan metode Diagram Piper Segiempat dan Stuyfzand. Hasil penelitian menunjukkan bahwa berdasarkan ketiga pendekatan yang dilakukan, airtanah pada lokasi penelitian tidak terdeteksi penyusupan air laut dan secara umum bersifat tawar. Pola aliran airtanah mengalir mengikuti topografi wilayah yaitu dari elevasi tinggi ke rendah, yang dominan mengalir menuju ke arah laut. Rekonstruksi hidrostratigrafi menunjukkan bahwa terdapat empat lapisan. Airtanah bebas ditemukan pada lapisan bermaterial pasir marin jenuh air tawar, di bawah lapisan zona aerasi. Lapisan dibawahnya terdapat akuitard yang tersusun atas material lempung marin bercampur lanau dan pasir marin halus dan mengandung airtanah payau. Lapisan terakhir tersusun atas material lempung berupa akuiklud yang mengandung airtanah payau hingga asin. Analisis hidrokimia berdasarkan metode Diagram Piper Segiempat membagi tipe airtanah ke dalam dua kelompok yaitu bikarbonat (I) dan semi-bikarbonat (II). Analisis hidrokimia berdasarkan metode Stuyfzand tipe airtanah terbagi atas F2-NaMix, F1-NaMix, g2-Ca(HCO3)2(+), dan F3-NaHCO3(+).

Excessive groundwater withdrawal will cause distortion at the interface which encourages seawater intrusion into groundwater. Saltwater intrusion degrades water quality of wells and consequently the water becomes unfit for use. This study aims to examine and analyze the potential for seawater intrusion into aquifers in the coastal area of Glagah, Temon District, Kulonprogo Regency, using the following analytical approaches: flownet pattern of unconfined groundwater; aquifer characteristics based on hydrostratigraphic reconstruction; groundwater characteristics based on unconfined groundwater hydrochemistry in the study area; and analyze the potential for seawater intrusion in the study area in terms of the three methods. Data collection and measurement of groundwater level and electrical conductivity values were done by sensus, while unconfined groundwater sampling was done by purposive sampling. Analysis of the pattern and direction of groundwater flow data was done by using linear interpolation. Hydrostratigraphic reconstruction based on geoelectrical estimation was obtained from secondary data in Santosa (2010). Data on the major ion content of groundwater samples were obtained from laboratory analysis and then the Charge Balance Error (CBE) was calculated to test the sample quality. Groundwater hydrochemical analysis was carried out based on the Expanded Square-Piper Diagram and Stuyfzand methods. The results showed that based on the three approaches taken, groundwater at the study site was not detected by seawater intrusion and was generally fresh. The pattern of groundwater flow follows the topography of the area, from high to low elevation, which predominantly flows towards the sea. Hydrostratigraphic reconstruction shows that there are four layers of aquifer zoning and distribution of material types. Unconfined groundwater is found in a layer saturated of fresh water made of marine sand, below the aeration zone layer. The layer below is an aquitard which is composed of marine clay material mixed with silt and fine marine sand and contains brackish groundwater. The last layer is composed of clay material in the form of aquicludes containing brackish to salty groundwater. Hydrochemical analysis based on the Expanded Square-Piper Diagram method divides the types of groundwater into two groups which are bicarbonate (I) and semi-bicarbonate (II). Hydrochemical analysis based on the Stuyfzand method of groundwater types is divided into F2-NaMix, F1-NaMix, g2-Ca(HCO3)2(+), and F3-NaHCO3(+).

Kata Kunci : Airtanah bebas, Intrusi air laut, Flownet, Hidrostratigrafi, Hidrokimia