The sangkarak river watersheds morphometric changes of Maros-Pangkajene Regency

Watersheds morphometric changes occur due to several factors, natural and or anthropogenic activities. The Sangkarak River Watersheds is one of the watersheds in Maros and Pangkajene Regencies with an area of 352.297 Ha, starting in Bantimurung area to the Makassar Strait. Since specific temporal data on the morphometric this watershed is not available and become obstacles for the fisheries management, this study aims to determine the dynamics of the watershed morphometric of Sangkarak river using remote sensing technology and Geographic Information System. The application used in this research is the DSAS (Digital Shoreline Analysis System) tool, which is an ArcGIS tool designed by USGS and ESRI to monitor shoreline movements. The data used in this research is the Landsat image data for 2002, 2008, 2013 and 2018. The results of the analysis of image data from 2002 to 2018 showed that there was a trend of river’s covering area decline up to 12.74 hectares, and presumably due to uncontrolled land uses.


Introduction
Sangkarak River Watersheds is one of the waterheds found in Maros-Pangkajene Kepulauan (Pangkep) Regencies, covering area up to 352.297 hectares. The source of Sangkarak River is in Bantimurung, Maros Regency and flow to Makassar Strait through Pangkep regency [1]. This river watersheds, is located in Rammang-Rammang Karst, a part of Maros-Pangkep Karst. Maros-Pangkep Karst, the second largest karst in the world after the one in South-Eastern China area, in part is included in Bantimurung-Bulusaraung National Park in South Sulawesi. Maros-Pangkep Karst is also known as habitat for many endemic species in Wallace region.
Rivers has an important role in the distributing water and nutrients, in water cycling and channeling surface water. In many rivers banks, cities are found since river provide water supplies and transportation. Rivers also provide agricultural lands and as for fisheries, rivers provide habitat and food for many aquatic organisms and source of livelihood. However, according to [2] land use changes of river watershed could cause the increase the amount of sediment deposited in river mouth hence changing the growth and form (river meander) and the speed of river flows. Morphometric changes of river watershed are caused by both natural process and anthropogenic activities such as deforestation, land mining, land uses, high precipitation and so forth [3]. The environmental and water quality changes could impact the aquatic live and its surrounding. In terms of fisheries, Muhtadi et al. (2017) [4] mentioned that changes in the river water quality will affect the fish composition structure of the river. Moreover, Gordon et al (1992) [5]  2 temperature will affect functional structure of fish communities, while river substrate structure and width changes will affect taxonomy structure of fish communities.
In accordance with increasing anthropogenic activities within Sangkarak River Watershed for more than two decades and their impact, directly or indirectly might change the morphometric of Sangkarak River, hence affecting the aquatic organisms in it. Therefore, this study aims at analyzing the morphometric changes of the Sangkarak River Watershed using Digital Shoreline Analysis System (DSAS) to provide reference for fisheries management of the area.     [7] is as follows:

Site and time
Note: NSM = Net River line Movement X 0 = Baseline distance to the old river line X 1 = Baseline distance to the newest river line EPR = Yearly river line changes t 0 = time of the old river line t 1 = time of the newest river line The NSM and EPR values were calculated from river line, river baseline and transect. The river line was measured from data of those five different years, having geometric value and coordinate system. As for the river baseline, is the baseline designated as the first point of transect in measuring the river line changes. The transect, also has geometric and coordinate system is put with distance 50 meters between transects and the length of 100 meters and 250 meters, depending on and adapting to the river line form and distance between the baseline and the farthest river line.

e. Analysis of land cover
The analysis was done using unsupervised method and the land cover classification was done twice. The first classification was done using composite band red, green and blue (band 321 on Landsat 7 and band 432 on Landsat 8). The second classification was done using composite band Near Infrared (NIR), SWIR-1, and Red (band 453 on Landsat 7 and band 564 on Landsat 8). This second classification was aiming to identified mangrove distribution [8]. As for land cover accuracy was done through overall accuracy test that is by counting the number of non-error samples divided by the total samples. The formula for the overall accuracy is [9]: N = X n / X 0 Note: N = overall accuracy X n = Number of non-error data/samples X 0 = Total number of samples used

River Morphometric Changes
The result showed that from 408 transects, the Sangkarak River has the highest erosion, 44.12% on its right side, while the highest sedimentation, 55.88% was found on its left side. The Sangkarak's river line changes on the right side of the river are shown at Figure 2. The result on the river line changes on the left side of Sangkarak River showed that 66.75% sedimentation and 33.25% erosion has occurred as presented at Figure 3.    Table 1.

Accuracy test
There were 92 sampling points from the total of 803 as results of transect numbers done by DSAS analysis. The value of overall accuracy test was 95%, therefore the map is feasible for further uses, as Anderson et al., (1976) [10] mentioned that the acceptability of the accuracy value in land cover mapping is 85% or 0,85.

Discussion
The highest erosion of Sangkarak River right hand side significantly found at Kecamatan Pangkajene, Pangkep Regency, with yearly average of 13,28 meters and the peak in the period of 2013-2018 due to flash flooding in 2013 [13]. On the other hand, the highest sedimentation was found on Sangkarak River left side at Kecamatan Bontoa within period of 2013 to 2018, amounted to 43.79 meters. Aside from the erosion from the river upper portion, image classification showed there is addition of 4.90 hectares mangrove in that area. Interviews to the settlers confirmed that there was mangrove rehabilitation activity, initiated by the fish ponds owners, to protect their fish ponds. According to Hogarth (2007) [14], mangrove ecosystem could slowing the river flow hence increasing the sedimentation brought by the river current.

Impacts of land cover changes to river morphometric
Landsat image interpretation year 2002 to 2008 discovered there was conversion of mangrove into fish ponds up to 353.79 hectares. This fact was the reason why sedimentation occurred in this river. Suwoyo et al., (2014) [15] research relate that 35.97% of fish ponds wastes are causing sedimentation to waters body.
Mangrove rehabilitation along the river banks done by fish farmers as well as people living on the river banks as "breakwater" and or for "extending fish ponds area" also has added to more vegetation cover of the Sangkarak River hence impacting the river morphometric.

River morphometric changes
Although the percentage of sedimentation on the Sangkarak river banks was higher than erosion, but sedimentation occurred because there is erosion or there is soil load carried by the river and deposited in the river basin [11]. The land cover data of Sangkarak River pointed out there was a narrowing area of 12.74 hectares due to the present of fish ponds and addition of vegetation along its banks. According to Strand and Pemberton (1982), one of the reason for erosion is land use degradation or damage, which in turn decreasing soil infiltration hence increasing the surface flow and causing erosion and at the end sedimentation.