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.

Macrodrenagem urbana: comparativo de hidrogramas gerados pelo método precipitação vazão, Soil Conservation Service (SCS), entre duas equações de chuva de boa confiabilidade

Este trabalho utiliza duas equações de chuva para calcular a vazão de pico de uma bacia hidrográfica localizada na região leste da cidade de São Paulo, a bacia do córrego Tiquatira. O modelo computacional utilizado, o HEC-HMS, permite realizar as simulações hidrológicas utilizando um método de precipitação vazão muito utilizado, o Soil Conservation Service (SCS). Na região da bacia em estudo, ocorrem frequentes inundações devido ao transbordamento do córrego Tiquatira, então se destaca a importância de utilizar a equação de chuva mais apropriada para a região, a fim de que um novo projeto de drenagem não subestime as estruturas hidráulicas a serem construídas. A equação de chuva desenvolvida por Martinez e Magni (1999) é bastante utilizada para os projetos de drenagem na cidade de São Paulo, portanto é uma equação de boa confiabilidade e consolidada. Porém a equação de chuva desenvolvida por Zuffo (2009), para a cidade de Guarulhos, apresenta maiores taxas de intensidades pluviométricas; ressalta-se que o posto pluviográfico de origem dos dados para o desenvolvimento dessa equação encontra-se próximo à região de estudo. Portanto foi apresentado o impacto que pode representar na vazão de pico utilizando as equações que inicialmente seriam recomendadas em uma bacia hidrográfica da região leste da cidade de São Paulo. Palavras-chave: Modelos hidrológicos. Urbanização. HEC-HMS. Equações de chuva.

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.

GIS-based approach for morphometric characteristics and development of hydrographs for the upper watershed of Jebba Reservoir, Nigeria

Nigeria's Jebba sub-basins are synonymous to frequent flooding, high rate of erosion, depletion of soil nutrients and unsustainable water use. The uncontrolled flooding may be a result of numerous factors related to topography, geology, climate and human activity. The present work was an attempt to describe the application of Geographical Information System (GIS) and Digital Elevation Model (DEM) for the estimation of morphometric characteristics of eight sub-basins in the upstream watershed of Jebba reservoir, Nigeria. Morphometric characteristics such as topographic, areal, relief and network were determined. Soil Conservation Service (SCS) technique was applied to estimate hydrographs. The study revealed that sub-basin number 3 had the lowest time of concentration and maximum depth of runoff while sub-basin number 2 had maximum ratio of circulation of 1.8 and it is tagged as the area that is highly prone to flood. The peak runoff in the sub-basins ranged between 330.10 and 924.86 m3/s (25-year return period) and for 100-year intervals ranged between 502.69 to 1408.40 m3/s. The estimated peak runoffs can be adopted for designing and constructing erosion control structures in the catchment area.

Analisis dan Pemetaan Limpasan Permukaan di DAS Citanduy Hulu dengan Metode SCSN

Abstrak. DAS Citanduy merupakan salah DAS yang terbesar di pulau Jawa dengan sungai utama adalah Cintanduy. DAS Citanduy terdiri dari beberapa sub DAS, salah satunya adalah sub DAS Citanduy Hulu. Perubahan tata guna lahan di DAS Citanduy Hulu terus terjadi, kondisi tsb telah mengakibatkan peningkatan debit banjir di sungai. Peningkatan debit di sungai diakibatkan adanya limpasan permukaan akibat hujan. limpasan permukaan dapat dianalisis menggunakan metode SCS (Soil Conservation Service). Metode SCS juga dianalisis berdasarkan kondisi tanah, sehingga dapat menentukan nilai Curve Number (CN) dari lahan. Hasil analisis tahun 2018, menunjukkan bahwa tutupan lahan 18,99% atau 13.735,97 ha berupa hutan (hutan primer, sekunder dan hutan tanaman). Sebaran jenis tanah di umumnya adalah Typic Dystrudepts (36,57%) dan Typic Hapludands (37,93%). Hydrological Soil Group (HSG) di DAS Citanduy Hulu didominasi oleh klas B sebesar 76, 92 %. Hasil analisis didapatkan bahwa DAS Citanduy Hulu tebal runoff maksimum pada PUH 2, 5, 10, 25, dan 50 tahun secara berurutan adalah 104 mm, 133 mm, 147 mm, 171 mm dan 187 mm. Tebal limpasan permukaan minimum dengan PUH 2, 5, 10, 25 dan 50 tahun secara berurutan adalah 17 mm, 31 mm, 39 mm, 53 mm dan 64 mm. Tebal limpasan permukaan menunjukkan potensi peningkatan debit banjir.Analysis And Mapping Runoff In Watershed Upper Citanduy With SCSN MethodAbstract. Citanduy watershed is one of the largest watersheds on the island of Java with the main river being Cintanduy. The Citanduy watershed consists of several sub-watersheds, one of which is the Upper Citanduy sub-watershed. Changes in land use in the Upper Citanduy watershed continue to occur, this condition has resulted in an increase in flood discharge in the river. The increase in discharge in the river is caused by surface runoff due to rain. Surface runoff can be analyzed using the SCS (Soil Conservation Service) method. The SCS method is also analyzed based on soil conditions so that it can determine the Curve Number (CN) value of the land. The results of the 2018 analysis show that 18.99% or 13,735.97 ha of land cover is forest (primary, secondary and plantation forests). The distribution of soil types, in general, is Typic Dystrudepts (36.57%) and Typic Hapludands (37.93%). Hydrological Soil Group (HSG) in the Upper Citanduy watershed is dominated by class B by 76.92%. The results of the analysis showed that the maximum runoff thickness of the Upper Citanduy Watershed at PUH 2, 5, 10, 25, and 50 years respectively was 104 mm, 133 mm, 147 mm, 171 mm, and 187 mm. The minimum surface runoff thickness with PUH 2, 5, 10, 25, and 50 years respectively is 17 mm, 31 mm, 39 mm, 53 mm, and 64 mm. The thickness of the surface runoff indicates the potential for increased flood discharge.

Pemodelan Tutupan Lahan Untuk Menjamin Keberlanjutan Debit Sungai (Suatu Studi Di Sub DAS Cikapundung-Maribaya)

Changes in land use in the Cikapundung watershed, ie changes in forest land to built-up land, have an impact on the quantity of river water. Changes in land use in the Cikapundung River catchment are not ideal conditions for absorbing water. If land conversion is not controlled, it can have a large impact on reducing the availability of water resources for subordinate areas or what is called water scarcity. Analysis that takes into account land use and discharge can be done with several hydrological analysis methods, one of them is the Soil Conservation Service Curve Number (SCS-CN) method. Based on the calculation, the CN value was changed in 2014 from 57.275 to 62.591 where land cover changes began to occur. Keywords: land use, river water, water scarcity, hydrology, CN value

Runoff assessment by Storm water management model (SWMM)- A new approach

The present study investigated the storm wise runoff collected in farm pond with the runoff estimated by Storm Water Management Model (SWMM) and Soil Conservation Service (SCS-CN) models. The SWMM and SCS-CN models estimated runoff depth storm wise. The runoff depths correspond to the catchment area given the runoff volume from the catchment. The runoff depth estimated from the Storm Water Management Model and Soil Conservation Service model was compared against the depth of runoff estimated from the Water balance model. For small rainfall depths, the runoff estimated from the Storm Water Management Model was at par with the actual runoff volume stored at the pond. It is necessary to know the watershed runoff contribution to the river or streams due to rainfall in order to determine environmental risk or flood potential. In larger rainfall depth, the runoff volume estimated from the SWMM model was less than the stored runoff volume at Farm Pond. The Soil Conservation Service Model gave better results for larger rainfall depth compared to Storm Water Management Model. SWMM was able to simulate runoff depth for small rainfall depths of 2mm. The peak runoff depths were produced by rainfall depths of 35.5mm. Initial abstractions of the study area for antecedent moisture content i.e. AMC I, AMCII and AMCIII are 53.2, 23.91 and 10.43mm, respectively. The comparison showed that both SWMM and SCS-CN models gave better runoff quantification results.