Electronic Theses and Dissertation

Hujan berperan besar dalam proses hidrologi, terutama limpasan permukaan dan erosi tanah. Intensitas hujan tinggi dengan laju infiltrasi rendah menyebabkan air mengalir di permukaan, membawa partikel tanah, dan memicu erosi, terutama pada lahan miring atau minim vegetasi. Untuk memahami hubungan antara intensitas hujan, sifat fisik tanah, limpasan, dan erosi, digunakan rainfall simulator yang mampu meniru hujan alami secara terkontrol. Alat ini memungkinkan pengamatan langsung terhadap limpasan, infiltrasi, dan erosi pada berbagai jenis tanah, termasuk sampel dari DTA Waduk Keuliling. Penelitian ini diharapkan menghasilkan data akurat sebagai dasar pengelolaan lahan dan pencegahan degradasi tanah. Tujuan dari penelitian ini adalah untuk mengetahui limpasan permukaan dan laju erosi berdasarkan pada jenis tanah dan kemiringan yang berbeda di Daerah Tangkapan Air Waduk Keuliling menggunakan rainfall simulator.
Penelitian ini terdiri dari dua tahap utama. Pertama, pengambilan sampel tanah dan analisis sifat fisiknya, meliputi penentuan lokasi, persiapan alat, pengambilan sampel tiga jenis tanah pada kedalaman 0–30 cm dan 30–60 cm, serta pengujian tekstur, kadar air, dan porositas. Kedua, pengukuran limpasan permukaan dan laju erosi menggunakan rainfall simulator pada kemiringan 10%, 15%, dan 23%. Alat dijalankan dengan mikrokontroler ESP32, mencatat durasi, debit, dan volume hujan buatan pada interval waktu tertentu. Volume limpasan diukur dari wadah penampung, dan sedimen yang terbawa air ditimbang untuk menghitung laju erosi.
Penelitian ini menunjukkan bahwa intensitas hujan, jenis tanah, dan kemiringan lereng mempengaruhi limpasan permukaan dan laju erosi di Daerah Tangkapan Air Waduk Keuliling. Setiap jenis tanah memiliki karakteristik fisik berbeda yang mempengaruhi infiltrasi dan erosi. Podsolik Merah Kuning bertekstur lempung liat berpasir hingga liat berpasir dengan porositas 49,54–51,72%, Latosol bertekstur pasir berlempung hingga liat berpasir dengan porositas 50,05– 53,53% dan infiltrasi tinggi, sedangkan Komplek Ransing dan Litosol bertekstur lempung liat berpasir hingga liat dengan porositas 52,17–52,44% dan infiltrasi rendah. Sebelum uji, Latosol menyimpan air terbanyak di lapisan atas (19,7%), sedangkan Komplek Ransing dan Litosol terendah (15–16%). Setelah uji, Komplek Ransing dan Litosol lapisan atas memiliki kadar air tertinggi (27,1%), menunjukkan air tertahan di permukaan. Karakteristik intensitas hujan bervariasi antar jenis tanah, di mana Podsolik mengalami lonjakan tajam, Latosol meningkat stabil, dan Komplek Ransing dan Litosol memiliki dua tahap kenaikan dengan lonjakan mendadak. Limpasan permukaan dan laju erosi meningkat seiring kemiringan lereng dan intensitas hujan, terutama pada tanah berporositas rendah atau berinfiltrasi rendah. Analisis regresi menunjukkan hubungan kuat antara intensitas hujan dengan limpasan dan erosi (R² 0,73–0,98), sedangkan hubungan limpasan dengan erosi lemah (R² < 0,22), menandakan pengaruh signifikan faktor lain seperti tekstur, kelembaban awal, dan struktur tanah. Penelitian ini menegaskan pentingnya mempertimbangkan kombinasi faktor fisik tanah, curah hujan, dan kemiringan dalam pengelolaan lahan untuk mengendalikan limpasan dan erosi.

Rain plays a crucial role in the hydrological process, particularly in surface runoff and soil erosion. High rainfall intensity combined with low infiltration rates causes water to flow over the surface, carrying soil particles and triggering erosion—especially on sloped areas or lands with minimal vegetation cover. To understand the relationship between rainfall intensity, soil physical properties, runoff, and erosion, a rainfall simulator is used to replicate natural rainfall under controlled conditions. This tool allows direct observation of runoff, infiltration, and erosion across various soil types, including samples collected from the Keuliling Reservoir Catchment Area (DTA Waduk Keuliling). The study aims to determine the surface runoff and erosion rate based on different soil types and slope gradients in the Keuliling Reservoir Catchment Area using a rainfall simulator. This research consists of two main stages. The first stage involves soil sampling and analysis of its physical properties, including site selection, equipment preparation, and collection of three soil types at depths of 0–30 cm and 30–60 cm, followed by laboratory testing of texture, moisture content, and porosity. The second stage involves measuring surface runoff and erosion rates using a rainfall simulator at slope gradients of 10%, 15%, and 23%. The simulator is operated with an ESP32 microcontroller to record rainfall duration, discharge, and volume at specific time intervals. Runoff volume is measured using a collection container, and sediment carried by runoff water is weighed to determine the erosion rate. The results show that rainfall intensity, soil type, and slope gradient significantly affect surface runoff and erosion rates in the Keuliling Reservoir Catchment Area. Each soil type exhibits distinct physical characteristics influencing infiltration and erosion. Podsolic Red-Yellow soils have sandy clay loam to clayey sandy textures with porosity ranging from 49.54% to 51.72%. Latosol soils, with sandy loam to clayey sand textures, have porosity values between 50.05% and 53.53% and demonstrate high infiltration capacity. Meanwhile, the Ransing Complex and Lithosol soils have sandy clay loam to clay textures, porosity between 52.17% and 52.44%, and low infiltration capacity. Before the rainfall test, Latosol soils retained the most water in the upper layer (19.7%), while the Ransing Complex and Lithosol had the lowest moisture content (15–16%). After the test, the upper layer of the Ransing Complex and Lithosol soils showed the highest moisture content (27.1%), indicating that water was retained on the surface. Rainfall intensity characteristics also varied among soil types: Podsolic soils experienced a sharp increase, Latosol soils showed a steady rise, while the Ransing Complex and Lithosol displayed two distinct increase stages with sudden peaks. Surface runoff and erosion rates increased with slope steepness and rainfall intensity, particularly in soils with low porosity or low infiltration capacity. Regression analysis revealed a strong correlation between rainfall intensity and both runoff and erosion (R² = 0.73–0.98), whereas the correlation between runoff and erosion was weak (R² < 0.22), indicating significant influence from other factors such as texture, initial moisture, and soil structure. This study emphasizes the importance of considering the combined effects of soil physical properties, rainfall characteristics, and slope gradient in land management strategies aimed at controlling surface runoff and soil erosion