Morphological Study of The Pulai Watershed on Bintan Island, Riau Island

¹ Aquatic Resources Management Study Program, Faculty of Marine Sciences and Fisheries, Raja Ali Haji Maritime University, Tanjungpinang, Riau Islands
² Environmental Science Study Program, Postgraduate Program, Raja Ali Haji Maritime University, Tanjungpinang, Riau Islands
³ Marine Science Study Program, Faculty of Marine Sciences and Fisheries, Raja Ali Haji Maritime University, Tanjungpinang, Riau Islands
⁴ Environmental Study Center, Raja Ali Haji Maritime University, Tanjungpinang, Riau Islands
⁵ Sei Jang Duriangkang River Basin Management Center, Riau Islands, Tanjungpinang, Riau Islands

^* Corresponding author: diana_azizah@umrah.ac.id

Abstract

The Riau Islands are a group of small islands whose entire land is divided into watersheds. One of the watersheds in the Riau Islands that is currently the main source of raw water for the community is Sei Pulai. The condition of the watershed on Bintan Island is greatly influenced by its morphometrics. The purpose of this study is to determine the morphological characteristics of the Pulai watershed on Bintan Island. This research was conducted in 2024 with observation by survey. Data processing is carried out by physical mapping of watersheds (soil, slope and geology). The results of the analysis showed that the Island watershed was included in the category of high rainfall (average rainfall of 2,500 -< 3,000 mm/year) but the intensity of rainfall was relatively low with an average ± 19.11 mm/day; the widest geological characteristics were composed of Pre-Tertiary and Quaternary sedimentary formations and igneous rocks consisting of granite and diorite; geomorphological characteristics consist of hills and undulating, rivers have low relief, laminar river flows and no rapids are found, with clear river water color; The slope of the Pulai watershed varies with class I slopes covering an area of ±412 Ha (7%); class II covering an area of ±4,071 Ha (74%); class III covering an area of ±897 Ha (16%); class IV covering an area of ±36 Ha (1%) and class V covering an area of ±83 Ha (2%); the shape of the slope of the Pulai watershed which has a hilly area with a sunken slope will produce a sharper hydrograph uplift. In general, the morphological characteristics of the Pulai watershed are geologically dominated by slopes of 8-15%, while geomorphology is dominated by the shape of old volcanic plains. Efforts are needed to rehabilitate and plant protected areas to overcome erosion caused by the slope of hilly land and fragile soil characteristics, especially protected areas outside forest areas during the rainy season.