Analysis of Surface Flow Rate (Runoff) on Land Use: Case Study in Loa Bakung Sub-District
Abstract
This study aimed to analyze the runoff rate on land use in the Loa Bakung Village. The results of this study are expected to be the basis for flood management in the region. The research was carried out from February-April 2021 at the Water and Soil Conservation Laboratory, Faculty of Agriculture, Mulawarman University. The object of this research is the land use of the Loa Bakung sub-district. The stages of conducting research are as follows: (1) preparation, (2) field observations, (3) data collection, (4) data processing, (5) interpretation, and (6) reporting. The data collected is in the form of; (1) an Administrative boundary map of the Loa Bakung sub-district, (2 Topographical maps, (3) Soil type maps, (4) Loa Bakung sub-watershed maps, and (5) Maximum rainfall data for the last ten years (2011-2020). This is done by calculating the surface flow rate using the rational method. The results showed that: (1) The results of the GIS analysis showed that there were five types of land use in Loa Bakung Village, namely shrubs, settlements, roads, mining, open land, and dry mixed agriculture. The use of shrubland has the largest area of 481.34 hectares, and the smallest island without vegetation, namely 27.18 hectares; (2) The highest runoff coefficient (C) is in the use of shrubland, namely 0.13463. While the value of Cor the smallest runoff coefficient is on the use of open land with a C value of 0.00493; and (3) The maximum runoff rate (Q) in the land use of Kelurahan Loa Bakung occurs in the 100-year return period (Q100) with a value of 157.4292 m3/sec and the lowest Q value appears in the five year return period (Q5) with a deal 86.1099 m3/sec.
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Introduction
Land use (land use) is an arrangement according to existing natural conditions. Its utilization requires interpretation, provision, and designation in a planned manner for use for the welfare of society.
Changes in the use of vegetation land to non-vegetative land are increasing in number inline with the increase in population, and the land is used for residential, office, industrial, and economic needs as well as other supporting facilities, which also have an impact both on the quantity of activity and the quality of the environment.
The transition of the function of an area that can absorb water into a watertight area will cause a hydrological imbalance and adversely affect the area. An area'schanges will impact the time and volume of surface runoff. In densely vegetated land, rainwater that falls will be retained on the ground, cover plants and seep into the soil through the vegetation so that surface runoff is small. In open land (without vegetation), most of the rainwater that falls will become surface runoff towards the river, so the river flow increases very quickly. An increase in surface runoff volume will cause flooding problems in the downstream watershed (Laoh, 2002).
Surface runoff is rainwater that flows over the surface of the ground. The amount of water that becomes this flow depends on the amount of rainwater per unit of time (intensity), the state of the ground cover, topography (especially the slope of the soil slope), the type of soil, and whether or not rain occurs Rahim, 2003).
The amount and speed of surface runoff depend on the catchment area and, most importantly, on the runoff coefficient and maximum rainfall intensity. Surface runoff with a high amount and speed often causes the displacement or transportation of soil masses on a large scale, causing flooding. The amount of water that becomes a stream causes the water to overflow, so the water stagnates in the area. Areas that are inundated or flooded will disrupt human activities. Human negligence in preserving nature and inaccurate land use has resulted in floods occurring in various locations, including the Loa Bakung area.
Loa Bakung Village is located in Sungai Kunjang District, Samarinda, whose area is dominated by the Kambisol-associated soil type. Rather steep topography and open land conditions. Land use in the Loa Bakung area consists of shrubs, settlements, mining, mixed dryland agriculture, and available land with a dominant Cambisol-associated soil type and rather steep topography.
This study aimed to analyze the runoff rate in the land use of the Loa Bakung Village. The results of this study are expected to provide information regarding the runoff rate in the land use of the Loa Bakung Village so that it can become the basis for handling the flood.
Conclusion
AND SUGGESTIONS 4.1 Conclusion Based on the results of research and discussion, it can be concluded as follows. 1) The results of the GIS analysis show that there are five types of land use in Loa Bakung Village: shrubs, settlements, roads, mining, open land, and dry mixed agriculture. The land use of shrubs has the largest area of 481.34 hectares and the smallest on land without vegetation, with an area of 27.18 hectares. 2) The highest runoff coefficient (C) is in shrubland, 0.13463. At the same time, the value of C,or the smallest runoff coefficient, is on the use of open land with a C value of 0.00493. 3) The highest surface runoff rate (Q) in the land use of Loa Bakung Village occurs in the 100-year return period (Q100) with a value of 157.4292 m3/sec, and the lowest Q value appears in the 5-year return period (Q5) with a value of 86, 1099 m3/sec. 4.2 Suggestion Based on this research, suggestions can be put forward, namely as follows: 1) Comparing land use in previous years to the surface runoff rate value is necessary. 2) It is necessary to carryout further research to reduce the value of Cor runoff coefficient, and it is necessary to carryout approaches in controlling surface runoff rates such as bioretention, infiltration wells, and others.
