PENGARUH PERUBAHAN REGIME ALIRAN DAN KENAIKAN PERMUKAAN LAUT TERHADAP HIDROTOPOGRAFI PADA IRIGASI PASANG SURUT

This research was done based on existing problems in the field related to hydrotopography changes at the tidal swamp land in West Kalimantan. After experiencing the process of developing a swamp area about 40 years, the level of agricultural productivity remains low. The low level of productivity is thought to be caused due to the low capacity of irrigation due to changes in land hydrotopography tidal swamp area. Hydrotopography is one of the aspects that influence the success of tidal irrigation. Hydrotopography shows how often a piece of land has been overwhelmed by fresh water, so hydrotopography strongly influenced by changes in river flow, sea level rise (SLR), and land subsidence. Previous research suggests a change in hydrotopography type, the change is due to the occurrence of land subsidence on tidal marsh area, that is the extent of hydrotopography types A and B were increased, but the extent of hydrotopography type C and D were decreased. How the hydrotopography changes due to the decline of flow regime and the rise of sea level is still unclear, so it is necessary to do this research. Therefore, this study aims to analyze the changes in the discharge from upstream rivers and sea level changes and their effect on the condition of land’s hydrotopography in the tidal swamp area. The study was conducted by modeling the terrain’s tidal marsh area of Pinang Luar, Kubu Raya district, West Kalimantan Province. The model used is a numerical model by using software that is relevant to the purpose of research. The variables to be reviewed are the amount of discharge of water from upstream rivers and sea level. The simulation was based on several types of hydrotopography scenarios, namely (1) the condition of channel dimensions according to plan in 2008 and the dimensions of the channel in field conditions (existing), (2) the boundary condition that differ in the value of water flow from upstream, high tides and adding value to high tides with and without sea level rise (SLR). The boundary conditions, the flow of water used in accordance with the amount of discharge during the rainy season, dry season, and the average water discharge that occurs in the upstream Kapuas River. The results showed that there have been changes in the flow regime of the river upstream, ie a decline in the trend of daily discharge in Kapuas River. The decrease is due to a decrease in hydrotopography type of flow regime of the river. The extent of hydrotopography’s variations on channel dimensions according to plan in 2008 are hydrotopographytipe B and C decreased by 3,5% and 25,2%, and the D-type hydrotopography was increased by 28,7%. Reduction of hydrotopography type B and C in the field conditions channel by 30% and 38,1%, whereas hydrotopography D-type increased by 68,1%. The changes of hydrotopography type are a result of sea level rise of 0,76 cm per year,on channel dimensions according to plan in 2008, the hydrotopography B-type and C-type have increased by 1,5% and 14%, while the D-type has decreased by 15,5%. The changes of hydrotopography in the field conditions channel, the hydrotopographyB-type and C-type have increased by 0,8% and 2,8%, while the D-type has decreased by 3,5%. The changes of hydrotopography alteration are due to a decrease in the flow regime and the water level rise occurring altogether, channel dimensions according to plan in 2008, the changes of hydrotopography B-type and C decreases by 1,1% and 25%, and hydrotopography D has increased by 26,1%. The changes in the field conditions channel of hydrotopography B-type and C decreased by 4% and 25,8%, whereas hydrotopography D-type increased by 29,8%. Changes in hydrotopography will cause modification to operation and maintenance of tidal wave irrigation. The land, originally a hydrotopography B-type turned into hydrotopography Ctype or C-type turns into D-type, causing the arrangement of water level on land will change accordingly. The changes in hydrotopography also cause modifications in the facilities and the infrastructure which have to be provided. Key words: flow regime, sea level rise, hydrotopography, tidal marsh

EFFECTIVE SEDIMENT CONTROL IN A RESERVOIR

Sedimentation in a reservoir cannot be avoided. The average rate of sedimentation on the storage volume reduction of a reservoir in the world is about 1 % per year (Yoon,1992), meanwhile, the storage volume reduction in several reservoir in Indonesia reaches 1,64% to 2,83% per year (Atmojo,2012). These sediment’s accumulations in the reservoir will continually reduce the storage volume, thus the intended functions of reservoirs for flood control (Atmojo, 2013), irrigation and water supply, electric generation, etc. will also reduced and not optimal. Some of sediment control measures have been practiced in reducing sediment accumulation in reservoirs around the world. In principle, there are two approaches i.e., reduce the sediment input to a reservoir by land conservation, construction of check dam, sand pocket, diversion channel, etc. and reduce the sedimentation in the reservoir by sluicing, turbidity current, dredging, and flushing (Morris and Fan, 1998; Emamgholizadeh et al., 2006). This paper presents the performance of sediment’s reduction from a reservoir by flushing, sluicing, and disturbing flushing based on some laboratories results (Atmojo,2012). It is expected that this paper can contribute to elicits some finding on the selection of which suitable method for sediment reduction from a reservoir

PENGELOLAAN DAERAH ALIRAN SUNGAI BERINGIN

Banjir tahunan yang terjadi di Sungai Beringin menyebabkan kerugian bagi masyarakat di sekitar Sungai Beringin, baik secara finansial maupun jatuhnya korban jiwa. Salah satu penyebab banjir Sungai Beringin dikarenakan perubahan tata guna lahan yang semula dari kawasan hutan menjadi daerah permukiman dan industri. Hasil dari penelitian menunjukkan bahwa DAS Beringin mengalami perubahan tata guna lahan yang signifikan dari tahun 1995 sampai 2015. Alih fungsi lahan tersebut menyebabkan debit banjir kala ulang 2 tahun meningkat dari 97,70 m3/dtk pada tahun 1995 menjadi 138,10 m3/dtk pada tahun 2015. Debit banjir ini melebihi prediksi debit banjir kondisi RTRW tahun 2011 – 2031 sebesar 112,40 m3/dtk. Skenario pengelolaan DAS Beringin efektif mereduksi debit banjir sebagai berikut pembangunan embung dengan kapasitas ± 27.780 m3 mampu mereduksi debit banjir dari 138,10 m3/dtk menjadi 95,20 m3/dtk atau sebesar 38,74%, sementara pembuatan sumur resapan sebanyak 7.978 buah dengan diameter 1,20 m dan kedalaman 3,00 m mampu mereduksi debit banjir dari 138,10 m3/dtk menjadi 101,00 m3/dtk atau sebesar 26,86%, dan penambahan Ruang Terbuka Hijau (RTH) mampu mereduksi debit banjir dari 138,10 m3/dtk menjadi 127,70 m3/dtk atau sebesar 7,53%.Kata kunci: DAS Beringin, debit banjir, tata guna laha

Simulation of Coastal Erosion Model to Support Disaster Mitigation in Coastal Sayung, Demak District

Coastal Sayung, Demak has occurred agricultural land and mangroves conversion for opening the ponds. Land use change inflict 2 small villages sink, namely Tambaksari (1997) and Rejosari (2004). The small villages are damaged by coastal erosion. This coast is an area affected by tides. The study aims to evaluate the erosion in coastal Sayung, by simulation model with mathematic model. The simulation results are calibrated with March and June 2016 bathymetry data. Bathymetry data is obtained by echosounder to acquiring contour depth. Wind data was obtained from NOAA for 10 years. Sediment sampling results indicate the type of silt (72%), clay (24%), and fine sand (4%), with specific gravity 1.51 – 1.85 tons/m3. The data used for hydrodynamics and erosion modeling with mathematic model. The simulation results indicate the greatest erosion value occurs in the transition season I, which is 94,000 m3. Patterns of erosion strongly influenced by the current patterns of a particular season. When the West, current and erosion patterns move towards northeast, and otherwise with the East. The most eroded villages are Sriwulan and Bedono, then Timbulsloko, and the smallest is Surodadi. The results of this study can be used to support disaster mitigation in the coastal Sayung, Demak. Keywords: bathymetry, coastal Sayung, erosion, mathematic model, sedimen

Pendugaan Limpasan Permukaan dengan Modifikasi Parameter Metode Soil Conservation ServiceCurve Number (SCS-CN)

Direct surface runoff is water flowing over the surface soil due to full capacity of soil infiltration. To calculate direct surface runoff at least 4 (four) main factors ie rainfall depth (P), soil type, land cover and land treatment. Currently, many models have been developed to analyze runoff from rainfall data commonly known as rainfall-runoff model. One model that simplified the complex hydrological cycle is known as the Soil Conservation Service (SCS) Curve Number (CN) or SCS-CN method has developed by United States Department of Agriculture (USDA) to estimate direct surface runoff and peak discharges in Watershed. Some researches suggest that to use this method outside the development site still needs adjustment its parameters. This research aims to modify SCS-CN method parameters in accordance with watershed conditions in Indonesia, with the following stages; (1) converting soil type based on Soil Mapping Unit (SPT) into the Hydrology Soil Group (HSG) from USDA; (2) comparing land cover class based on SNI 2010 into land cover class at USDA; (3) Determine CN matrix based on result between converting soil type and comparing land cover class, (4) Specify the maximum retention coefficient value (λ) on SCS-CN method. The results of this research conclude that determinants factors in estimation of direct surface runoff are as follows: 1) SPT conversion based on soil taxonomy in Indonesia at sub-group level, there are 7 (seven) sub-groups of soil type at research location, (2) Land cover class from USDA to land cover class according to SNI 2010 is from 66 classes to 125 classes, (3) result of matrix formulation CN value with land cover type in accordance with SNI (2010) and HSG, obtained 500 pairs of land cover types and HSG, (4) Direct surface runoff separation method using Straight Line Method dan Master Depletion Curve Method. and (5) λ value in Indonesia is 0.11, with CN composites at reseach location is 57.7. Keywords: curve number, direct surface runoff, land cover, land treatment, maximum retention coefficient value, soil type

PEMODELAN OPTIMASI GUNA LAHAN UNTUK PENGENDALIAN BANJIR PERKOTAAN (Studi Kasus: Kota Samarinda, Provinsi Kalimantan Timur)

Bencana yang sering terjadi dan paling banyak merugikan di wilayah Indonesia adalah banjir.Kerugian akibat banjir mencapai dua pertiga dari semua bencana alam yang terjadi. Masalah banjir pada umumnya terjadi akibat adanya interaksi berbagai faktor penyebab, baik yang bersifat alamiah maupun faktor yang diakibatkan kegiatan manusia. Adapun salah satu tindakan manusia yang dapat menyebabkan banjir adalah penggunaan lahan (land-use) yang tidak sesuai. Kondisi penggunaan lahan seringkali masih kurang memperhatikan konservasi tanah dan air, terutama kesesuaiannya terhadap kemampuan dan peruntukan lahan sehingga kemampuan infiltrasi tanah menjadi berkurang yang mengakibatkan nilai limpasan permukaan semakin besar. Pemodelan optimasi guna lahan pada dataran banjir sangat diperlukan untuk memaksimalkan proporsi penggunaan lahan yang sesuai untuk mengendalikan banjir. Pemodelan optimasi guna lahan mancakup 3 (tiga) bagian yaitu model spasial penentuan kawasan banjir, model spasial penentuan peruntukkan lahan dan model hidrologi untuk optimasi guna lahan. Dari pemodelan tersebut maka dapat dihasilkan kawasan rawan banjir, ketidaksesuaian lahan dan luasan lahan yang perlu dikonversi atau direkayasa agar menghasilkan debit yang dapat ditampung oleh sungai. Penggunaan SIG (Sistem Informasi Geografis) sebagai alat analisis akan semakin mempermudah dalam mengaplikasikan model yang telah dibuat melalui input data skoring dan pembobotan yang kemudian dilakukan tumpang susun secara sistematis sehingga menghasilkan peta tingkat kerawanan banjir dan arahan peruntukkan lahan. Sedangkan HEC-HMS dan HEC-RAS digunakan untuk menentukan proporsi optimal masing-masing jenis penggunaan lahan sehingga dapat mengendalikan banjir melalui rekayasa guna lahan dengan pertimbangan kawasan rawan banjir dan peruntukkan lahan. Model diaplikasikan di Kota Samarinda, Provinsi Kalimantan Timur dikarenakan wilayah Kalimantan merupakan kawasan banjir terluas di Indonesia, sedangkan Kota Samarinda pernah mengalami banjir besar pada tahun 2008 sehingga dianggap dapat mewakili wilayah lain sebagai studi kasus.Dari penelitian ini dapat diketahui bahwa faktor yang berpengaruh terhadap banjir meliputi ketinggian, kelerengan, curah hujan, jenis tanah, guna lahan , dan zona rawan luapan sungai, dimana ketinggian dan guna lahan memiliki dominasi pengaruh. Ketidaksesuaian guna lahan pada kawasan dengan elevasi tinggi akan semakin meningkatkan kerawanan banjir, karena debit banjir(Q) menjadi lebih besar. Proporsi guna lahan yang optimal pada suatu DAS tidak dapat disamakan antara DAS satu dengan lainnya, karena memiliki keberagaman topografi dan curah hujan. Setiap sub DAS yang memiliki kawasan rawan banjir diprioritaskan untuk memiliki hutan > 10% luas DAS sebagai kawasan resapan. Kata Kunci: banjir, guna lahan, model, perkotaan Disasters that often happen and caused many hazard impacts in Indonesia is flood. The hazard impact can reach two of three from all disaster that happen. Flood problems generally happen caused by interaction of many factor, such as natural and human activity factor. One of human activity that can caused flood is land used that not suitable. The land used condition is often not based on land and water conservation, especially about suitability for land capability, so it caused land infiltration came more less and run off value more increase. Land Used Model on flood land is very important to optimize the land used proportionthat is suitable to control flood. The model has 3 (three) elements, spatial model to determine flood area, hydrologic models to optimized land used, and spatial model to recommended area. GIS are used as analyst tools that will make more easily in applicating model that has madewith scoring and weighted input then overlayed systematically so can produced hazard level of flood area and recommended area. HEC-HMS and HEC-RAS use to optimizedland use proportion that can controlled flood. Model will be applicate in Samarinda City, East Kalimantan Region because of Kalimantan Region is the largest flood area in Indonesia, and Samarinda City has big flood disaster in 2008 so it can representing the other area as case study. From this study, it is known that factors influencing the occurrence of flooding include the altitude, slope, rainfall, the type of soil, land use, and river flood-prone areas, where the altitude and land use have dominant effects. Land use incompatibility in areas with a high altitude will increase vulnerability to flooding, as flood discharge (Q) becomes bigger. The proportion or the optimal land use proportion in a watershed can not be compared one another, because it has different topography and rainfall. Each sub-watershed that has flood-prone areas should have forests by >10% of the area of the watershed as catchment areas. Keywords: flood, land used, model,urba

KAJIAN RESPON PERUBAHAN PENGGUNAAN LAHAN TERHADAP KARAKTERISTIK HIDROLOGI DAS GARANG

Pengurangan areal hutan dan peningkatan areal terbangun menyebabkan meningkatnya koefisien limpasan yang pada akhirnya berakibat meningkatnya debit aliran sungai pada musim penghujan dan kekeringan pada musim kemarau. Model ekohidrologi dapat membantu memahami fenomena tersebut. Tujuan penelitian ini adalah untuk memprediksi perubahan karakteristik hidrologi DAS Garang dengan menggunakan model SWAT, mengetahui pengaruh perubahan penggunaan lahan terhadap perubahan karakteristik hidrologi; dan untuk menyusun rekomendasi perencanaan penggunaan lahan terbaik di DAS Garang. Data debit dan data iklim diperoleh dari instansi terkait. Kalibrasi model menggunakan 2 metode yaitu metode otomatis dengan menggunakan program SWATCUP.Sufi2 dan metode manual (trial and error). Model di kalibrasi dan divalidasi menggunakan data debit harian yang berasal dari stasiun pengamatan simongan. Model menghasilkan NSE (Nash Sutcliffe Coefficient) sebesar 0,769, R2 (R square) sebesar 0,867, dan PBIAS sebesar -7,54. Selama kalibrasi, dan NSE, sebesar 0,755; R2 sebesar 0,755 dan PBIAS 0,34 selama validasi. Hasil penelitian ini menunjukkan bahwa Karakteristik hidrologi DAS Garang tahun 2013 menunjukkan aliran permukaan sebesar 1711,49 mm, dengan aliran dasar sebesar 638,68 mm, denga nilai koefisien aliran dan koefisien regim aliran masing-masing sebesar 0,55 dan 23,04. Perubahan penggunaan lahan 2000 dan 2013 berpengaruh terhadap karakteristik hidrologi yaitu dengan peningkatan aliran permukaan sebesar 301,88 mm (14,64%) dan nilai koefisien aliran menjadi 0,55. Penggunaan lahan yang direkomendasikan berupa penerapan agroteknologi dengan tindakan teknik pengelolaan lahan pergiliran tanaman sesuai kontur dan kombinasi dengan teras. Kata kunci : Model SWAT, DAS Garang, koefisien aliran, koefisien regim aliran Depleting forest and the increase of build-up area make run off coeficien increase. Those also will increase stream flow at rainy season, but will decrease at dry season. SWAT (Soil and Water Assessment Tools) as one of ecohydrologi models will help us to analyze that phenomenon. The objectives of this study were to predict hydrological characteristics changes at Garang watershed, to know the impact of land use changes to hydrological characteristics and to know the best land use planning Garang watershed. Observation data were obtained from appropriate institution such as stream flow and climate data. The calibration used SWATCUP. Sufi2 and manual (Trial and error) methods. The methods resulted 13 parameters for calibration. The model was calibrated and validated by using the average daily data from AWRL Simongan. The models yielded NSE (Nash Sutcliffe Coefficient) was 0,769, coefficient of determination R2 (R-square) was 0,867, PBIAS was -7,54 during calibration and NSE was 0,755, R2 was 0,755 and PBIAS was 0,34 during validation. These results of this study indicated that the hydrological characteristics of Garang watershed were surface run off by 1711,49 mm, with base flow (638,68 mm), coefficient run off (0,55) and regime coefficients (23,04). The change of land use from 2000 – 2013 increased surface run off abaout 301,88 mm (14,64%) and run off coefficient became 0,55. The recommendation of this study is to apply agrotecnology such as crop rotation associates with contour and terrace combinations. Kaywords : SWAT model, Garang watershed, runoff coefficient, coefficient of flow regim

PERILAKU MASYARAKAT DALAM MENGELOLA SAMPAH DI KOTA BIMA NUSA TENGGARA BARAT

Perkembangan kota-kota di Indonesia menimbulkan permasalahan pembangunan seperti permasalahan transportasi, urbanisasi, permukiman kumuh, sanitasi yang buruk, penyediaan air bersih hingga permasalahan persampahan perkotaan. Sampah menjadi masalah besar perkotaan di Indonesia, tidak hanya kota besar bahkan Kota Bima pun mengalami masalah persampahan. Sebagai kota perdagangan dan kota transit, menyebabkan terjadinya akselerasi pembangunan yang memicu meningkatnya pertumbuhan jumlah penduduk dari tahun ke tahun sehingga mengakibatkan meningkatnya aktivitas penduduk

The Influence of Coastal Protective Building against Erosion in Sayung Coastal, Demak

In 1980, land conversion of mangrove occur in large numbers since the opening of the Causeway. Flooding and Rob have already begun to be felt since the year 1995 and beginning in 2000 has been sinking a Dukuh village near by Bedono. Year 2000 erosion occurred in district Sayung, Demak and in 2013 the large area known erosion area of 400 – 1300 acres along the coastline. To reduce and overcome the damage done by the shore, re-purposed soft structure (conservation) and hard structure (breakwater). The purpose of this research is to know the influence of the building protective coast against erosion. The method used is the quantitative methods i.e. include survey field and numerical modelling methods. Research results in the form of changes in the rate of erosion in Coastal Sayung Keywords: Coastal, Coastal Building, Erosion, Sediment