Pengaruh Perubahan Tutupan Lahan terhadap Debit Banjir di Daerah Aliran Sungai Ciliwung Hulu

Jakarta yang berfungsi sebagai pusat pemerintahan dan bisnis Indonesia seringkali mengalami permasalahan bencana banjir. Kejadian banjir yang terjadi tidak hanya disebabkan oleh tingginya intensitas hujan yang terjadi namun juga dipengaruhi oleh faktor-faktor lain, khususnya perubahan tutupan lahan yang memperkecil daerah resapan air hujan.. Studi ini merupakan suatu upaya untuk memprediksi dampak perubahan tutupan lahan yang terjadi terhadap dinamika banjir yang melanda ibu kota Negara Indonesia ini. Penelitian ini terbagi dalam 3 bagian yaitu pengumpulan data, pemodelan hidrologi dan analisis sensitivitas banjir terhadap perubahan tutupan lahan. Hidrograf Sintetis SCS CN digunakan untuk analisis hidrologi untuk mendapatkan peningkatan debit dan volume limpasan. Analisis hidrologi menunjukkan perubahan tutupan lahan berdasarkan tren yang tercatat menyebabkan peningkatan debit puncak dan volume limpasan pada tahun 2030 masing-masing sebesar 26% dan 24%. Namun demikian, dengan mengikuti Rencana Tata Ruang Kabupaten Bogor dan sekitarnya, peningkatan pengaruh banjir terhadap debit puncak dan volume limpasan dapat diminimalisir hingga berturut-turut sebesar 5.26% dan 4.94%. Setiap 13 km2 kawasan hutan atau pertanian yang diubah menjadi kawasan perkotaan atau tanah kosong, debit puncak banjir dan volume limpasan meningkat sebesar 4.63% dan 4.34%.

Application of Risk Analysis in the Screening of Flood Disaster Hot Spots and Adaptation Strategies

In recent years, Taiwan has established a sound flood control foundation in terms of river management. Due to climate change and land development, surface runoff has increased. In addition, the functions of flood control engineering facilities have their limits. Surface runoff cannot be fully absorbed by rivers, and frequent floods still occur in some areas. According to the characteristics of water flowing along the terrain to low-lying land, the terrain features can be used to find out the hot areas prone to flooding and the appropriate location of flood storage space for improving flooding. On the basis of the natural terrain environment, the disaster risk framework is used to manage environmental complexity, and to carry out research on flood warning and governance decision-making systems, so that human beings can coexist with the uncertainty of flood risk. In this study, the Zhuoshuixi Basin was used as the sample area, the SCS-CN method was used to analyze the excess runoff, and the risk concept was used to establish a flood evaluation model. In addition, through the changes in land use, the SCS-CN method estimates the difference of potential maximum retention, quantifies the variation of excess rainfall in each watershed division, and uses the digital elevation model to calculate the depression site to analyze the relationship between the difference of potential maximum retention and the depression space of the watershed. The results show that the adaptation strategy for high-risk flooded areas should be strengthened, and areas with large water storage space and a small potential maximum retention difference can be the best location for offsite compensation.

ASSESSING THE IMPACT OF URBANIZATION ON DIRECT RUNOFF IN DISTRICT 8, HO CHI MINH CITY

Ho Chi Minh City (HCMC) is among the cities that are most at risk of fl ooding worldwide. Urbanization processes have led to a change in land use, which in turn has resulted in an increase in impervious surfaces and runoff , thus again leading to the risk of fl ooding in the city. The aim of the article is to study the impact of urban development (on the example of District 8 of HCMC) on surface runoff using a combination of the interpretation of remote sensing images of the earth (ERS) Google Earth and the SCS-CN model (the Soil Conservation Service curve number). Theoretical models are used to analyze the relationship between the typology of buildings and areas of open and impervious surfaces. The interpretation of remote sensing images was carried out in the ArcGIS program. The method used to calculate surface runoff is the Soil Conservation Service Curve Number (SCS-CN) method developed by the US Soil Conservation Service and is suitable for assessing the eff ects of land-use/land cover change due to urbanization. The results of the study show the volume of surface runoff in areas with diff erent levels of urbanization in district 8 of HCMC, assessing the impact of urbanization processes on surface runoff and revealing new opportunities for managing this process. The combination of remote sensing interpretation and SCS-CN model makes it possible to assess the impact of urban development on surface runoff . Urbanization and an increase in built-up area strongly aff ect fl ooding, reducing the soil retention.

Pengaruh Perubahan Penggunaan Lahan terhadap Volume Runoff di Kawasan Perkotaan Yogyakarta Tahun 2008 – 2018

Kawasan Perkotaan Yogyakarta mencakup seluruh wilayah Kota Yogyakarta dan sebagian Kabupaten Sleman serta Bantul. Setiap tahunnya penggunaan lahan mengalami perubahan terutama pada Kawasan Perkotaan Yogyakarta, disertai dengan perubahan intensitas hujan. Penelitian ini berfokus pada hubungan perubahan penggunaan lahan dengan volume runoff. Perubahan penggunaan lahan diklasifikasikan menggunakan metode unsupervised berdasarkan citra Landsat 5 dan 8 dengan interval 5 tahunan (2008, 2013, dan 2018). Volume runoff maksimum dikalkulasi menggunakan metode SCS-CN. Hubungan kedua hasil tersebut dianalisis dengan metode korelasi Pearson. Hasil penelitian menunjukkan bahwa selama tahun 2008 – 2018 luas lahan terbangun meningkat sebanyak 19,5% dari 11.755,6 ha pada tahun 2008 menjadi 14.059,5 ha pada tahun 2018. Volume runoff mengalami peningkatan sebanyak 76,6% dari 7.268,68 m3 pada tahun 2008 menjadi 12.837,63 m3 pada tahun 2018. Hal tersebut dibuktikan dengan tingginya signifikansi hasil nilai korelasi dibawah 5% dengan t- hitung lebih besar dari t-tabel. Korelasi Y menunjukkan jika lahan terbangun bertambah 100 ha maka terdapat kenaikan volume runoff sebanyak 76.09 m3. Korelasi Y untuk lahan terbuka jika bertambah 100 ha maka terdapat kenaikan volume runoff sebanyak 59.27 m3. Pada lahan vegetasi, jika luas lahan vegetasi bertambah 100 ha, volume runoff akan bertambah 54 m3. Hal ini menunjukkan bahwa semakin luas penggunaan lahan terbangun maka volume runoff juga semakin besar.

Modelling the Event-Based Hydrological Response of Mediterranean Forests to Prescribed Fire and Soil Mulching with Fern Using the Curve Number, Horton and USLE-Family (Universal Soil Loss Equation) Models

The SCS-CN, Horton, and USLE-family models are widely used to predict and control runoff and erosion in forest ecosystems. However, in the literature there is no evidence of their use in Mediterranean forests subjected to prescribed fire and soil mulching. To fill this gap, this study evaluates the prediction capability for runoff and soil loss of the SCS-CN, Horton, MUSLE, and USLE-M models in three forests (pine, chestnut, and oak) in Southern Italy. The investigation was carried out at plot and event scales throughout one year, after a prescribed fire and post-fire soil mulching with fern. The SCS-CN and USLE-M models were accurate in predicting runoff volume and soil loss, respectively. In contrast, poor predictions of the modelled hydrological variables were provided by the models in unburned plots, and by the Horton and MUSLE models for all soil conditions. This inaccuracy may have been due to the fact that the runoff and erosion generation mechanisms were saturation-excess and rainsplash, while the Horton and MUSLE models better simulate infiltration-excess and overland flow processes, respectively. For the SCS-CN and USLE-M models, calibration was needed to obtain accurate predictions of surface runoff and soil loss; furthermore, different CNs and C factors must be input throughout the year to simulate the variability of the hydrological response of soil after fire. After calibration, two sets of CNs and C-factor values were suggested for applications of the SCS-CN and USLE-M models, after prescribed fire and fern mulching in Mediterranean forests. Once validated in a wider range of environmental contexts, these models may support land managers in controlling the hydrology of Mediterranean forests that are prone to wildfire risks.

ANALISIS STATUS DAYA DUKUNG AIR DI SUB DAS CIKERUH MENGGUNAKAN METODE SOIL CONSERVATION CURVE NUMBER (SCS-CN)

Sub DAS Cikeruh merupakan kawasan dengan laju pertumbuhan penduduk yang tinggi, yang mana hal tersebut mengakibatkan alih fungsi lahan terjadi di beberapa kecamatan sehingga berimplikasi terhadap menurunnya ketersediaan air dan meningkatnya kebutuhan air di Sub DAS Cikeruh. Penelitian ini bertujuan untuk mengetahui status daya dukung air di Sub DAS Cikeruh melalui perbandingan rasio antara kebutuhan dan ketersediaan air. Kebutuhan air dihitung dengan menggunakan standar yang ditentukan oleh SNI 19-66728.1, 2002; SNI 67281-2015; dan Ditjen Cipta Karya Dinas PU tahun 1996, adapun sektor yang dihitung adalah domestik, non domestik, industri, pertanian, peternakan, dan perikanan. Ketersediaan air dihitung dengan mengestimasi volume aliran yang terjadi di Sub DAS Cikeruh menggunakan metode Soil Conservation Service Curve Number (SCS-CN) dari USDA dengan melibatkan data hidrologi dari tahun 2011 hingga 2020. Hasil penelitian menunjukkan bahwa ketersediaan air di Sub DAS Cikeruh pada tahun 2020 adalah sebesar 351.852.088,9 m3/tahun, sedangkan kebutuhan air di Sub DAS Cikeruh mengalami perubahan yang dinamis setiap tahunnya. Kebutuhan air di Sub DAS Cikeruh pada tahun 2011 adalah sebesar 545.250.212 m3/tahun, tahun 2015 sebesar 711.121.596 m3/tahun, sedangkan tahun 2020 sebesar 520.638.257 m3/tahun. Hasil perhitungan menunjukkan bahwa terjadi defisit air di Sub DAS Cikeruh, dimana nilai kebutuhan air lebih tinggi dibandingkan ketersediaan air, adapun rasionya sebesar 0,641, yang artinya daya dukung lingkungan telah terlampaui (overshoot) karena nilai rasio < 1.

Dinâmica hidrológica da Bacia hidrográfica do Rio Subaé-BA

Monitorar os processos hidrológicos em uma bacia hidrográfica apesar de ser fundamental, por vezes se torna bastante complexo, principalmente devido a escassez de dados. Nesse sentido, o presente estudo objetivou gerar modelos hidrológicos da Bacia Hidrográfica do Rio Subaé, Bahia, Brasil, em ambiente SIG, utilizando como base o método Curva Número (CN). Para tanto, foram utilizadas imagens do Satélite LandSat8 (30m), MDE do Satélite ALOS, sensor PALSAR (12,5m), arquivo vetorial de solos na escala 1:250.000 do IBGE e dados pluviométricos do INMET. Os dados adquiridos foram processados em ambiente SIG, utilizando o Classificador supervisionado Bhattacharya, o algoritmo r.watershed e o método SCS-CN. Os resultados foram mapas de Uso e Cobertura do Solo, Escoamento Superficial e Taxa de Escoamento. A partir dos resultados foi possível inferir que o somatório das características naturais, como Relevo, Solo e Precipitação em conjunto com fatores antrópicos, dentre os quais ressalta-se a ocupação urbana desordenada, proporcionam aumento do escoamento superficial que além de resultar em inundações no perímetro urbano, sugerem um maior risco quanto à erosão do solo e degradação hídrica na área de estudo.

Gravel Mining Activity Impact on Riverbed Erosion and Bridge Foundation Stability

Geomorphological processes pose a risk that deserves attention and planning to avoid that, especially in the section near to east of Tuz bridge. This section of the valley facing a dramatic increase in gravel excavation and sorting of aggregates, consequence led to a change in the pattern of river branches flow from an anabranching river to a single-channel river, which led to a concentration of river discharge during floods. On 9th December 2018, Tuz Bridge was failed due to a heavy rainstorm three days preceding the failure event. The current study aims to conduct a field survey of all the human activities in the study area to assess river changes from remote sensing data the amount of runoff and river peak discharge based on rainfall data using SCS-CN method. In this study, ArcGIS, ArcGIS Earth, Google Earth, and WMS software are incorporated in the data analysis. The revealed results indicate the severe modification of valley morphology and converting the river pattern to flow during flood within a single channel with flow speed exceeded the critical velocity to induce vertical erosion of gravel and sands under the foundations of the bridge and causing the displacement and settlement of the bridge. The study recommends the local administration prevent gravel mining from the river valley at the upstream area of the bridge

Estimation and Analysis of Rainfall Runoff for Urban Hydrology using TR 55 SCS CN and GIS Approach in Hebbal Valley of Bengaluru, South India

Urban floods are increasing frequently and severely. Climate change is usually attributed to urban floods with insufficient evidence. While in certain cases this appears to be true, the influence of landscape change in urban growth is more important. This study analyses development of an urban landscape with the complexity of established cities and combines physiographic data for the assessment of peak surface runoff in the study area, Hebbal valley. A portion of the Cauvery river basin draining into the Pinakini river in the district of Bangalore. It encompasses a 305.21 sq.km region in East Bengaluru and North Bengaluru. The land use and land cover classification was classified as 14 different categories: dark, light, roads and vegetation. The region of study has undergone unpredictable expansion and changes in the Land Use Land Cover in the last two decades. Several flood occurrences have occurred in different regions of Hebbal Valley throughout recent years. Rainfall analysis conducted between 1970 and 2018 with 1596mm of greatest precipitation. For the study, several space and non-space data were collected and thematic maps were produced. Runoff estimates for 2018 were made for 24 micro water sheds in the Hebbal Valley using SCS-CN TR55 technique for urban hydrology. The objective of this study is to determine the quantity of peak runoff produced, to develop better urban management techniques. The finding shows that rush volume has increased in recent years as land use patterns have changed and precipitation intensity has increased substantially over shorter periods. The study suggests spatial intervention efforts to provide suitable buildings and measures for flood flow.

Pengaruh Tutupan Lahan terhadap Base Flow Index DAS Way Seputih Provinsi Lampung

Tujuan penelitian ini adalah menganalisis nilai Base Flow Index (BFI) dan debit baseflow DAS Way Seputih; menganalisis nilai Curve Number (CN) composite DAS Way Seputih tahun 2005, 2009, dan 2011; serta menganalisis pengaruh perubahan tutupan lahan terhadap baseflow DAS Way Seputih. Penentuan baseflow tahun 1973-2006 menggunakan Metode RDF (Recursive Digital Filter) terbaik berdasarkan uji kinerja, yaitu Root Mean Square Error (RMSE), R2, dan grafik FDC (Flow Duration Curv) di antara metode Lyne&Hollick, EWMA, Chapman Algorithm, dan Nathan and McMahon. Kemudian Metode RDF terbaik ini dibandingkan dengan Model SCS-CN (Soil Conservation Sevice Curv Number) untuk menentukan baseflow dan BFI tahun 2005, 2009, dan 2011 berdasarkan uji kinerja. BFI DAS Way Seputih tahun 2005, 2009, dan 2011 berturut-turut adalah 0,8178; 0,54225; dan 0,649502. Untuk nilai CN I composite, CN II composite, dan CN III composite tahun 2005 berturut-turut adalah 63,9191; 79,8869; dan 80,1315. Nilai CN I composite, CN II composite, dan CN III composite tahun 2009 berturut-turut adalah 42,7834; 60,8427; dan 83,6676. Sedangkan Nilai CN I composite, CN II composite, dan CN III composite tahun 2011 berturut-turut adalah 66,4066; 81,9460; dan 94,5943. Nilai BFI dipengaruhi oleh debit baseflow dan debit sungai. Debit sungai dipengaruhi oleh curah hujan, sedangkan debit baseflow dipengaruhi oleh perubahan luas tiap jenis tutupan lahan.