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Trend Analysis Variations and Relation Between Discharge and Rainfall: a Study on Kushiyara River

M. E. Uddin
Department of Geography and Environment, Shahjalal University of Science and Technology, Sylhet

S. A. Akter
Department of Geography and Environment, Shahjalal University of Science and Technology, Sylhet

M. J. Uddin*
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail

M. T. M. Diganta
Department of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Tangail

Abstract/ Executive Summary:

Water resources and rivers play a very important role in economy and agriculture. But due to climate change and improper management, water resources are losing the natural discharge capacity from upper stream. This study was under taken to find out the trends and variability of rainfall and discharge at two stations of the Kushiyara River. Rainfall and discharge data Daily time series data of stream flow or discharge at Sheola (1976 to 2007) and Sherpur (1982 to 2007) and observed discharge data in certain interval from 2008 to 2016 have been analyzed in this study. For trend analysis, Mann-Kendall Test (MK) and Sen’s Slope Estimator method were used as non-parametric test and relationship assessment was done by undertaking Pearson’s Coefficient of Correlation. Annual discharge at Sheola and Sherpur station showed downward trend and maximum discharge was found downward trend at both stations. In Mannkendall test and Sen’s Slope Estimator method showed downward trend in most cases. Climate change and improper land management may have influenced the present condition.

Keywords: Annual and seasonal rainfall, Kushiyara river, Seasonal discharge, Trend analysis

Location: Kushiyara River within Sylhet and Maulvibazar district

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Non-commodity: Rainfall, Trend analysis

Objectives:

Objective of the study was to assess the annual and seasonal discharge of Kushiyara River at Sheola station and Sherpur station; to appraise the annual and seasonal rainfall of Kushiyara River at Sheola station; to analyze the trend of discharge of Kushiyara River at Sheola and Sherpur station; to find relation of discharge between Sheola and Sherpur station; to analyze the trends in Rainfall at Sheola Stationand to find relation between discharge at Sherpur station and rainfall at Sheola station.

Methodology:

This study area of this research was Kushiyara River within Sylhet and Maulvibazar district. Kushiyara River is a Trans-boundary Rivers of Bangladesh. Kushiyara River originates from the northern hills of Assam in India where it is known as Barak and then it flows further creating the border between Nagaland and Manipur states. The river enters Bangladesh along 24°53' north latitudes and 92°32' east longitudes after flowing westward from Milchar in Kachar district (India). Kushiyara River has a lengthof about 161 km with an average width of 250m and in the monsoon season the mean depth of the Kushiyara reaches up to 10m.For the collection of hydrologic data, two gauging stations were selected which are known as Sheola and Sherpur. Sheola station locates in Sylhet district and Sherpur Station locates in Maulvibazar district. Selection of two gauging station was based some factors such as hydrologic conditions or characteristics are not same at all places of river course, upper stream and lower stream shows different characteristics of discharge, lower stream discharge always depends on upper stream discharge, rainfall station of Sheola which is located near the upper stream of river has contributed to lower stream discharge by runoff, base flow etc. Daily time series data of stream flow or discharge at Sheola (1976 to 2007) and Sher pur (1982 to 2007)and observed discharge data in certain interval from 2008 to 2016 have been analyzed in this study. Total period of discharge data is 42 years at Sheola station and 35 years at Sherpur station. In other hand, daily time series data of Rainfall at Sheola station have been analyzed. Time period of rainfall data is 40 years which is 1977 to 2016. All of time series data are secondary data which have been used in this study. These data are collected from government authorized organizations. Discharge (from 1976 to 2007) of Sheola station and discharge (from 1982 to 2007) of Sherpur station and rainfall (from 1977 to 2008) of Sheola station have been collected from National Water Resource Database (NWRD) founded and maintained by Water Resource Planning Organization (WARPO). Base map of Sylhet and Maulvibazar district are collected from website of Local Government Engineering Department (LGED).In trend analysis, there are two types of trend test which one is parametric test and another one is non-parametric test. Mann-Kendall Test (MK) and Sen’s Slope Estimator method is used as nonparametric test. Non-parametric data is more reliable forhydrologic data. It was used to making decision on trend. Mann-Kendall’s trend test The non-parametric Mann-Kendall test is commonly employed to detect monotonic trends in series of environmental data, climate data or hydrological data.The purpose of the Mann-Kendall (MK) test (Mann 1945; Kendall 1975; Gilbert 1987) is to statistically assess if there is a monotonic upward or downward trend of the variable of interest over time. Main benefit of this test is that the data need not conform to any particular distribution. No assumption of normality is required (Helsel and Hirsch, 1992). It is highly recommended for general use by World Meteorological Organization (Mitchell et al., 1966). The hypotheses of Mann and Kendall’s trend test is H0 = Time series values are independent and identically distributed i.e. there is no trend. HA = There is a monotonic (not necessarily linear) trend. So, it is a teo-tailed test. The test statistic, S (score) is then computed as Where, sign (yj-yi) is equal to +1, 0, or -1, n is the total number of observation. A positive value of S indicates an ‘upward trend’ and a negative value of S indicates ‘downward trend’. It has been documented that when n>=8, the statistic S is approximately normally distributed with mean. Statistical Analysis Pearson’s coefficient of Correlation is used to show the relationship between variable. Discharge-discharge, discharge-rainfall relation is determined by correlation. Relation is spectacled by percentage. Probable error (PE) is calculated to examine the significance of correlation. Coefficient of correlation is calculated to determine the dependency rate of dependent variable on independent variable. All types of data were processed and analyzed by using Microsoft Office 2013, Minitab 18 and MAKESENS 1 0. The Maps had been prepared by using Arc GIS 10.3 software. After data entry had been completed, simple one way tables and graphs had been prepared for the analysis to make the report more understandable.

Source of Information: J. Environ. Sci. & Natural Resources, 10(2):121–132, 2017 ISSN 1999-7361

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Main targets of study are trend analysis, relation of discharge and rainfall. Mann-kendall test, Sen’s slope and correlation have been conducted to achieve these targets. Besides these, monthly variation of rainfall and discharge have been analyzed in this study. Coefficient of variation hasbeen used to find monthly variation. Statistical methods have been conducted to this study. Fromthis research, it has been appeared that annual discharge of Kushiyara River is decreasing and rainfall at Sheola station is also decreasing. Sedimentation, transportation, irrigation and fishing are strongly links to river. Decreasing trend of yearly discharge at Kushiyara River might affect the water demand to meet the needs of growing communities, farmers, energy producers and manufacturers. Irrigation and navigation would be affected severely. Rainfall is decreasing year to year. Irrigational and sedimentation activities will be hampered due to scarcity of rainfall. In winter season, monthly variation of rainfall is maximum than other seasons. So it needs to take proper plans for replenish the surface water management otherwise surface water condition would be worse.

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