ASSESSMENT OF FLASH FLOOD HAZARD POTENTIAL IN A SMALL MOUNTAINOUS CIKUNDUL WATERSHED IN CIANJUR, WEST JAVA, INDONESIA

Flash flood is a geomorphic hazard that can cause huge losses in a short period of time. Cianjur regency, especially Cikundul Watershed is a flash flood frequent area. Therefore, flash flood potential mapping is needed to reduce the threat that can be caused by flash flood. In the flash flood potential mapping, Flash Flood Potential Index (FFPI) method is still rarely applied in Indonesia. This study aims to see the comparison of flash flood potential areas based on models developed in the FFPI method which is Smith, Brewster, Krudzlo, and Ceru models. The four models used slope, land use, soil texture, and vegetation cover as variables. Spatial analysis and statistical test was implemented to validate the flash flood potential areas with flash flood affected locations. The result reveals that Cikundul Watershed was dominated by moderate potential areas based on Brewster, Krudzlo, and Ceru model but low by Smith model. The result also reveals that 65% of 68 Sub-Sub Watershed have different potential and 35% have same potential. High potential areas in all four models was distributed in the Upper Cikundul Watershed. The Crosstab Fit Test result shows that Smith model is the closest model to the actual event

HYDRODYNAMICS MODELING IN KENDARI BAY, SOUTHEAST SULAWESI, INDONESIA

Kendari Bay is coastal water in the center of the capital city of Southeast Sulawesi province. It is shaped like a pocket with a narrow mouth and there is an estuary of a large river, namely the Wanggu river, which makes the dynamics of its waters very interesting to study. The focus of the study is the hydrodynamic factors in the Kendari Bay and Wanggu River areas. This study aims to examine the hydrodynamic conditions of Kendari Bay, mainly due to the existence of reclamation and the influence of the Wanggu River which has not been studied previously. This research method uses a two-dimensional model based on bathymetric data, tides, and the flow of the Wanggu River with a simulation time of 15 days (1 March to 15 March 2020). The modeling results were then verified with PUSHIDROSAL tidal elevation data showing an RMSE value of 0.07 indicating that the model was well constructed. The mixed tidal type with a tendency to double daily is the tidal type of Kendari Bay waters based on the Formzahl number value of 0.51. The current pattern generally moves in and out from east to west and vice versa with a varying elevation range following spring conditions of 1.75 m. The maximum tidal speed is 0.1784 m/s and the minimum value is 0.0057 m/s which is shown in the sample results of the model when the hing to low tide, and low to high tide. The results of the hydrodynamic modeling show that the current velocity increases when passing through a narrow path, namely the bay estuary and river estuary. The existence of the reclamation area affects the changes in the velocity of the current which is significantly larger and the direction of the current that undergoes a deflection follows the shape of the reclamation area. The current direction is to the southeast and then turns towards the northeast when low to high tide and eastward then turns towards the northeast when the high to low tide spring conditions compared to research before the reclamatio

PREDICTIVE MAPPING OF CRITICAL LAND IN BENGAWAN SOLO WATERSHED: AN INTEGRATED APPROACH USING LANDSAT IMAGERY AND TERRAIN ANALYSIS

Inappropriate land use can have negative impacts, increasing the risk of land becoming critical. Managing critical land and growing human needs is essential to balance land and water resources. This research aims to map necessary land in the Bengawan Solo watershed. The research method integrates remote sensing and geographic information system (GIS) methods. Critical land analysis was conducted based on the Regulation of the Director General of Watershed and Protected Forest Control Number P.3/PDASHL/SET/KUM.1/7/2018, which is used as a reference in determining whether land is categorized as critical land. The regulation uses 4 (four) variables in its processing: land cover variables, slope, erosion hazard level, and forest area. The study results show land criticality in the Bengawan Solo watershed in 2023. Most areas have low slopes (0-8%), considered non-critical, covering 30.50% of the total area. In contrast, the Potentially Critical category (8-15%) dominates with 45.94% of the area, indicating potential risks in moderately steep areas. Areas with steeper slopes fall into the Critical (10.29%) and Very Critical (2.68%) categories

UTILIZATION OF SPOT 6/7 AND LANDSAT TO ANALYZE OPEN GREEN SPACE AND BUILT AREA IN SURABAYA CITY

The migration of people from rural to urban areas is a common phenomenon nowadays. One of the goals of urbanization is in the city of Surabaya. The increase in population causes the need for housing and the need for life to increase. One of the many changes in land use is the change of land into built-up land. The increase in the area of built-up land currently raises a new phenomenon where the area of open space is reduced due to changes in land use, one of the changes in land use is from green open space to built-up land. This study aims to see the extent to which the growth trend of green open space and built-up land in the city of Surabaya by using the NDVI method to see the trend of changes in green open space in the city of Surabaya and NDBI for the land built in the city of Surabaya. The data used in this study are SPOT 7 images for green open space and Landsat 8 for built land. Based on this method, green open space in the city of Surabaya in 2015 was 29.19%, in 2016 it was 21.22%, then in 2017 it was 24.54 %, and in 2018 it was 27.60%. While for Built land in 2015, it was 26.43%, in 2016 it was 26.44%, in 2017 it was 30.99% and in 2018 it was 42.88%. Other results were also obtained for the change of green open space into the land. awakened has increased every year, namely from 2015 to 2016 by 2.67%, from 2016 to 2017 by 4.43%, and from 2017 to 2018 by 8.08%. As for the land built into green open space, namely 2015 to 2016 of 2.01%, 2016 to 2017 of 2.84%, 2017 to 2018 of 2.72%. The conclusion from this activity is that NDVI can be used to see the level of vegetation density which can indicate the existence of green open space in urban areas. And NDBI can show the existence of built-up land. The city of Surabaya, has stable green open space, while the built land continues to increase every year

UTILIZATION OF GEOGRAPHIC INFORMATION SYSTEM BASED ON UNMANNED AERIAL VEHICLE (UAV) FOR DETAILED MAPPING OF SRIWEDARI CULTURAL HERITAGE COMPLEX IN SURAKARTA CITY

Sriwedari cultural heritage complex in the City of Surakarta, Middle Java, is one of the buildings from the golden era of Keraton Kesunanan of Surakarta. Sriwedari park was built as a recreation area, entertainment, and recreation place for the Keraton family, which is why it’s called “Kebon Rojo” (Park of King). Besides being a park, there are a couple of other cultural heritage buildings like Radya Pustaka museum, Wayang Orang Building, Sriwedari Stadium, and Segaran. According to the Ministry of Education and Culture Republic of Indonesia, Sriwedari has become a kind of cultural heritage in the form of sites. The purpose of this research (1) Utilization of spatial based technology using a Geographic Information System that can map in detail the location of cultural heritage with the data sources from the Unmanned Aerial Vehicle (UAV) complete with the coordinate position and supporting information; (2) 3D Visualization using GIS-based software for distributive functional communication media that is communicative for the people. There are three stages of methods in this research. First, license/permission and collecting coordinate data (Ground Control Point) GCP, data of object distance in the field, and other information related to functions of every building. Second, UAV data processing uses spatial-based software, Agisoft Photoscan, and ArcGIS. Third, 3D and 2D map visualization about the building detail, function, and other information is available at Sriwedari Cultural Heritage Complex

SPATIO-TEMPORAL ANALYSIS OF CHANGES IN CORAL REEF AREA USING LANDSAT 8 SATELLITE IMAGERY ON PARI ISLAND, KEPULAUAN SERIBU, DKI JAKARTA

Coral reefs are ecosystems that are sensitive to change. High pressure can cause damage to coral reefs. Monitoring the condition of coral reefs needs to be done to know the current condition. One way that can be used to monitor coral reefs is by utilizing remote sensing. The research was conducted to know the changes in the coral reef area and the factors that influence the changes in the coral reef area in Pari Island, Kepulauan Seribu, DKI Jakarta in the period 2013 to 2022. The research was conducted using Landsat 8 image data from 2013 to 2022. Image data processing was done with an object-based classification method. Coral cover measurements were conducted using the Line Intercept Transect (LIT) method. The results showed a change in coral reef area of 7.02 ha with the condition of live coral cover ranging from 27-43% which is included in the fair category. The results of field measurements show that the condition of water parameters falls into the unsuitable category. The increase in area that occurred was thought to be due to management activities carried out by the Pari Island community and activities carried out by LIPI in 2016, namely conducting coral reef restoration. The decrease in area is partly due to coastal reclamation activities, destructive tourist activities, and parameter conditions

COMPARATIVE ACCURACIES USING MACHINE LEARNING MODELS FOR MAPPING OF SUGARCANE PLANTATION BASED ON SENTINEL-2A IMAGERY IN KEDIRI AREA, EAST JAVA

Data collection in smallholder sugarcane plantations is still very sensitive to the subjectivity of informants and data collectors. In the meantime, the problem with data collection on sugarcane plantation companies is a low response rate. This situation can reduce the precision of the estimates that are produced. Consequently, the goal of this research is to recognize sugarcane fields using the machine learning models on Sentinel-2A satellite imagery in Kediri Area that covering Kediri Regency and Kediri Municipality, East Java. Along with developing machine learning algorithms, this research will evaluate how well LightGBM performs when compared to other algorithms, including CART, SVM, Random Forest, and XGBoost. Each model employed hyperparameter tuning with random search and stratified 10-fold cross validation to avoid overfitting. The process of labelling satellite imagery using images from Google Street View, then predictor variables used are NDVI, NDWI, NDBI, EVI, and elevation. The most accurate classification model obtained was LightGBM, with a 98% accuracy and a cohen’s kappa of 97.7%. The estimated area of sugarcane plantations in the Kediri Regency and Kediri Municipality in September 2022 is 18,897.6 ha and 571.87 ha.

SPATIAL TEMPORAL ANALYSIS OF LAND USE CHANGES IN AREAS VULNERABLE TO EARTHQUAKES AND LANDSLIDES, (Case Study: Cianjur Regency)

Cianjur Regency is a regency that is vulnerable to earthquakes and landslides. This is because the Cianjur Regency is crossed by the Cimandiri Fault which is actively moving. Meanwhile, the population growth rate in Cianjur district has increased based on data from Badan Pusat Statistik (BPS) for 2020-2021. Population growth causes many problems, especially the problem of space. Built-up land will be higher as the population increases. This study uses the temporal spatial analysis method of land use with variables of land use in 2013 and 2022, Earthquake Vulnerability Index, and Landslide Vulnerability Index. This variable was obtained based on the processing of Landsat 8 Satellite Imagery data in 2013 and 2022 and disaster vulnerability raster data from Badan Nasional Penanggulangan Bencana (BNPB). The results of this study are a temporal spatial analysis of changes in land use from 2013 - 2022 for earthquake-vulnerable areas and landslide-vulnerable areas. Changes in the use of built-up land to the Landslide Vulnerability Index experienced an increase in area in all categories. In contrast, the Earthquake Vulnerability Index only experienced an increase in the medium and high categories

SPATIAL ANALYSIS OF QUANTITATIVE PRECIPITATION FORECAST ACCURACY BASED ON STRUCTURE AMPLITUDE LOCATION (SAL) TECHNIQUE

Quantitative Precipitation Forecast (QPF) is the final product of a short-term forecasting algorithm (nowcasting) based on weather radar data which is widely used in hydrometeorological aspects. The calculation of the accuracy value using point data on a rainfall gauge often causes a double penalty problem because the QPF prediction results are in the form of spatial objects. This study aims to apply object-based spatial verification in analyzing the accuracy of QPF based on the Short Term Ensemble Prediction System (STEPS) algorithm using the SAL technique. The verification process is carried out by calculating the index value of the structure component (S), amplitude (A), and location (L) in the QPF prediction results based on the results of weather radar observations. The index values for components S and A have a range of -2 to 2, and 0 to 1 for component L with a perfect value of 0. The case study used is the occurrence of heavy rains that caused flooding in Bogor Regency in 2020. SAL verification results from 26 case studies used shows the average value of the components S, A, and L, respectively 0.51, 0.38, and 0.21. As many as 75% of all case studies have S and L component values less than 0.5 which indicate the structure and location of the QPF prediction object is close to the structure and location of the object of observation. A positive value in component A indicates that the QPF prediction results based on the STEPS algorithm tend to be overestimated but on a low scale, namely 0.38 out of 2