Hydrology of the Sirba River: Updating and Analysis of Discharge Time Series

The Sahelian regions are affected by an increasing number of catastrophic floods in recent years as a consequence of climate and land use/land cover changes. River flow data is key to understanding river behavior and develop flood mitigation and prevention strategies. The present study provides a revision and an update of the existing discharge dataset of the Sirba River with the aim of enhancing the reliability of these data. The revision also includes the recalibration of the Garbey Kourou rating curves. The analysis of the revised discharge time series strengthens the previous findings, evidencing a positive trend in flood frequency and intensity over the entire analyzed period of 1956–2018. This positive trend is more pronounced for the last 40 years due to a significant underestimation of the rating curves used. A relevant finding is a new changepoint in the time series, detected for 2008, which represents the beginning of the period in which the highest flood magnitudes were registered. The effect of land use/land cover changes and climate changes on the water resource is depicted using flow duration curves. This research produces a revised and more reliable discharge time series that will be a new starting point for future hydrological analyses.

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Perceived Human-Induced Causes of Landslide in Chattogram Metropolitan Area in Bangladesh

10.21203/rs.3.rs-216876/v1 ◽

2021 ◽

Author(s):

Zia Ahmed ◽

A H M Belayeth Hussain ◽

Mufti Nadimul Quamar Ahmed ◽

Rafiul Alam ◽

Hafiz-Al Rezoan ◽

...

Keyword(s):

Land Use ◽

Time Series ◽

Land Cover ◽

Metropolitan Area ◽

Land Cover Changes ◽

Land Use Land Cover ◽

Weak Soil ◽

Landsat Images ◽

Level Of Education ◽

Steep Hill

Abstract This study investigates Land Use Land Cover changes in the Chattogram metropolitan area, the second largest city in Bangladesh. Using a questionnaire survey of 150 local inhabitants, the study explores perceived human-induced causes of landslides. Using time series Landsat images this study also analyzes Land Use Land Cover changes from 1990 to 2020. The analysis reveals built-up area extended rapidly during 1990 to 2020. In 1990, total built up area was 82.13km², which in 30 years, stood at 451.34km². Conversely, total vegetative area decreased rapidly. In 1990, total vegetation area was 364.31km², which reduced to 130.44 km² in 2020. The survey respondents identified extensive rainfall, hill cutting, steep hill, and weak soil texture as several reasons for landslide. Findings show that age and experience of facing landslide are two significant predictors to explain whether excessive hill cutting is solely responsible for landslide. Level of education and experience of facing landslide are statistically significant in explaining building infrastructure as solitary cause to landslide. Gender, age and income of the respondents significantly explain deforestation as the only responsible for landslide. Finally, gender, level of education, and income of the respondents significantly explain only excessive sand collection causes landslide.

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