Umboro Lasminto

Fractal Characteristic Analysis of Watershed as Variable of Synthetic Unit Hydrograph Model

Fractal characteristic of watershed is an important parameter which influences the formation of synthetic unit hydrograph. Based on a previous study, hydrology response of watershed expressed in hydrograph form could be well presented by hydrology network characteristic as a form of fractal characteristic of watershed [1]. Fractal characteristic of watershed was stated as fractal dimension which was presented in three parameters i.e. river branch ratio (RB), river length ratio (RL) and watershed river area ratio (RA). The purpose of this research was to analyze fractal characteristic and to verify its fractal dimension stability as preliminary research to prepare variables which would be used to develop synthetic unit hydrograph model in the future. Analysis was undertaken using two methods i.e. Horton’s Coefficient Ratio and Box Counting Dimension. Analysis result revealed that fractal dimension of river network from 8 watersheds calculated using those two methods could give almost the same result, ranged from 1 to 2. Fractal dimension from calculation also showed similarity with study conducted by Tarboton et al. [2], Balkhanov et al. [3], Khanbabaei et al. [4], obtaining that fractal dimension of river network is generally in the range of 1 to 2.

A synthetic unit hydrograph model based on fractal characteristics of watersheds

ABSTRACT Synthetic unit hydrograph (SUH) is one of the rainfall-discharge transformation models that are still popularly used today primarily for estimating flood discharge for water resources planning and management. The advantage of this model is that it is able to estimate the discharge based on the sequence of time in an occurrence of rainfall, and thus the correlation between time and discharge in the form of hydrograph can be obtained. The fundamental weakness of SUH is that they are likely to produce deviations for watersheds that do not have the hydrological characteristics similar to the watersheds used as the basis for the model’s development. These deviations are estimated as a result of the assumptions used to establish the concept of unit hydrograph and the complexity of the factors affecting hydrograph, particularly the nature of rainfall and watershed characteristics that are not accommodated in the model, including fractal characteristics of watersheds that are considered highly influential on the formation of a hydrograph. This research was conducted at eight watersheds in Central Sulawesi-Indonesia to develop and construct an SUH model. The model was constructed by using some parameters based on a combination of main fractal and morphometric characteristics of a watershed. This research successfully formulated a peak time equation (Tp) as a function of the length of the main stream (L), the ratio of stream length (RL) and the density of stream network (D) with a determination coefficient (r2) of 99.8%, a base time equation (Tb) as the function of area of a watershed (A) and slope of main stream (S) with a determination coefficient of 98.2%, a peak discharge equation (Qp) as a function of peak time and a simple single curve equation derived from Gamma Distribution Equation. The validation of SUH models at eight watersheds in Central Sulawesi shows that all the main hydrograph parameters evaluated showed a very good performance.

Simulating the arrangement of subsystem to reduce inundation in the drainage system of Pepelegi housing area Sidoarjo

Pepelegi Indah Resident is a place which is frequently inundated by floodwater. This condition happened since the drainage system was designed with inappropriate waterflow method. The concern of this research was to figure out alternatives by managing the floodwater from the disposal drainage system. The existing information showed the area would be inundated if rainfall occurred for 2-3 hours. Half of Pepelegi Indah Resident would be inundated and subsidence time of flood on vulnerable time was 5-24 hours. To reduce the floodwater, some scenarios or simulations were carried out among others the management of tertiary drainage, the pool accommodation, and the provision of pumps at the enable point. From the simulation, the researcher should choose the best scenario which worked and optimally reduce the flooding. Based on the simulation results, the best scenario is the pool accommodation with new pumps at the primary channel.

Parameters Estimation of Synthetic Unit Hydrograph Model Using Multiple Linear and Non-linear Regressions

The use of synthetic unit hydrograph model (SUH) is remain popular used to transform rainfall into run off for water resources development. The typical feature of this model is that the main equation represents the shape of the curve expressed by the relationship between time and discharge. In addition, the SUH model is also expressed in three parameters i.e. peak time (TP), peak discharge (QP), and base time (TB), representing the hydrograph curve equation. In general, SUH model is developed based on morphometry parameters of watershed, especially watershed area (A), main river length (L) and main river slope (S). Another approach in hydrograph modelling is based on the fractal characteristics of watershed. This study aims to develop a synthetic unit hydrograph model based on a combination of morphometry and fractal characteristics of watersheds. The three model parameters (TP, QP and TB) were predicted using multiple linear regression and compared with multiple nonlinear regression. The results of the analysis show that the two methods showed excellent performance. The estimation of SUH parameters using linear regression resulted peak time equation (TP) as function of river length (L), ratio of river length (RL) and density of drainage network (D) with determination coefficient of 99.8%, a base time equation (TB) as the function of watershed area (A) and river slope (S) with determination coefficient of 98.2%. Using multiple non linear regression, estimation of SUH parameters formulated peak time equation (TP) as function of river length (L), ratio of river length (RL) and ratio of watershed area (RA) with determination coefficient of 99.9%, a base time equation (TB) as the function of watershed area (A) and ratio of watershed area (RA) with determination coefficient of 97.9%. Peak discharge equation (QP) is stated as a function of peak time and a simple single curve equation derived from Gamma Distribution Equation.

Studi Angkutan Sedimen Sudetan Pelangwot-Sedayu Lawas Sungai Bengawan Solo

Sungai Bengawan Solo merupakan salah satu sungai terpanjang di Indonesia yang mengalir mulai dari area hulu di Kabupaten Wonogiri dan Ponorogo hingga ke area hilir di Kabupaten Gresik. Perubahan fungsi lahan di area hulu dan peningkatan debit yang melalui Sungai Bengawan Solo membuat banjir terjadi di area hilir sungai yakni di Kabupaten Bojonegoro dan Kabupaten Gresik. Sudetan Pelangwot sepanjang 13 km merupakan saluran yang dibuat untuk mengurangi debit banjir yang terjadi dengan mengalirkannya ke laut Jawa. Namun dikarenakan pendangkalan yang terjadi akibat sedimentasi, kapasitas Sudetan Pelangwot dalam mengalirkan debit menurun. Tugas akhir ini bertujuan untuk menganalisa sedimentasi yang terjadi pada sudetan Pelangwot dengan menggunakan program bantu HEC-RAS 4.1.0 Konsep yang digunakan dalam pengerjaan tugas akhir ini adalah dengan memodelkan Sudetan Pelangwot menggunakan program HEC-RAS 4.1.0 kemudian melakukan simulasi aliran sudetan untuk mengetahui sedimentasi yang terjadi. Dari hasil simulasi yang dilakukan dengan menggunakan program HEC-RAS 4.1.0 diketahui perkiraan volume sedimentasi yang terjadi di sudetan selama musim penghujan dari tanggal 1 Desember 2010 hingga 21 Mei 2011 adalah sebesar 325.030,23 m 3 . Agradasi terjadi di sebagian besar penampang sudetan sedangkan degradasi hanya terjadi di beberapa titik. Kantong sedimen dapat dibuat sebagai upaya pengendalian sedimen pada dasar saluran sudetan di tiga titik yang berbeda dengan kapasitas total 175.875 m 3 .Pemeliharaan kantong sedimen dilakukan setiap 3 bulan sekali dengan melakukan pengerukan pada kantong sedimen.