The Role of Human Activities in Streambank Stability: Lower Sakarya River (NW Turkey)

Abstract

The main objective of this study is to determine historic and current human impacts on streambank stability in Lower Sakarya River. Remote sensing and Geographical Information System techniques with conjunction field works were performed to identify the impact of human alteration on streambank stability in the riverine environment of the eastern portion of Sakarya province. LULC (land use/cover) and historical streambank changes were analyzed from Landsat 1-5 Multispectral Scanner (MSS), Landsat-7 Enhanced Thematic Mapper Plus (ETM+), and Google Earth images between 1995 and 2016. As results, a significant LULC changes have been observed along the buffered zone due to population growth. Recently, change in LULC type from agricultural to urban usage has changed river equilibrium. The stream channel also became more stable and straight as man-made modifications including a hydropower (HES) dam constructed in 2010, which primarily reduced flood frequency, water velocity, stream power, shear stress on sediment particles temporarily deposited along the streambank. After the year of 2010, downstream portion of the dam had experienced narrowing and expanding mid-channel bars. Moreover, the channel has been slightly moved towards east especially along urbanized and sinuous courses. The streambank displacement ranged from 2.9 m to 36 m in the region. Instream mining activities and bridge constructions in the region also disturb active streambanks, which raise a concern about instability of streambank and potential damage to infrastructures. Such studies are extremely important for understanding basic mechanisms of streambank evolution for further river restoration practices.

Urban Flood Event and Associated Damage in the Benue Valley, Nigeria

“…At least 64.3% of the respondents claimed to be forewarned about the likelihood of a flood event by the Nigerian Meteorological Agency and the Nigerian Association of Hydrological Science but were not sure of the magnitude. Duru (2017) noted that the Benue State Commissioner for Water Resources and Environment noted that they 'were actually aware that there would be flooding but it was the magnitude we (that they) did not know'. With such warning, a youth organization typically embarked on campaign to sensitise the vulnerable communities on cleaning of many blocked drainage channels (Plate 1) that have been implicated for preventing free runoffs, and consequently aggravating flooding.…”