A02

Impact of river-damming and sand-mining on bank erosion in the Vietnamese Mekong Delta〇Basil WIETLISBACH, Doan BINH, Giovanni DE CESARE, Sameh KANTOUSH, Tetsuya SUMI

Recently, the lives and economy of local people inafter the procedure illustrated in Figure 1.

the Vietnamese Mekong Delta (VMD) are threatened

The resulting surface change between the two years

due to increasing river bank (RB) erosion, coastline

for each RB extraction approach is then compared toretreat, subsidence and other changes in the region.

the one obtained from a geometrically corrected

Among various causes for these processes, theGoogle Earth data set. In this reference data set, thereduction in the sediment supply from the upper

RB of the study site was digitized manually for 2014

Mekongbyand 2019 and the surface change between the twohydropower dams together with large-scale aggregate

years was calculated using the same approach as formining in the riverbed and its tributaries is to highlight.

the Landsat data set (Figure 1). The best performing

While the impacts of the dams in sediment reduction

RB extraction approach is identified.

Riverduetosediment

trapping

in the VMD have been investigated by someFinally, to further increase the accuracy of theresearchers, the associated impacts of such sedimentextracted RB position, spectral mixture analysis is

reduction on RB erosion and the pernicious effects ofperformed on the before identified, best performing

sand mining in the VMD has little known.

RB extraction technique. Its basic idea is to identify
the amount of water contained in a pixel square

The present study analyses in a first step thearound the extracted RB and to shift the RB position

performance of different RB extraction methodologies

accordingly. This procedure results in a sub-pixelin the context of the VMD for Landsat imagery. Theaccuracy. The result is validated comparing it again toselected

the reference data set.

methodologies

include

NDVI,

NDWI,

MNDWI, WNDWI and AWEInsh. They are based on
spectral indices which are the result of two or more

In a second step, the identified RB extraction

spectral bands to enhance the discrepancy between

technique is used to analyze the RB dynamic within awater bodies and land. To segment their outputs

100 km long segment of the Mekong river in the

finally

intosegmentationwaterandmethods

land,
arethreedifferent

VMD from 1982 to 2019. Based on the results, theapplied:default

impact of dam construction and sand mining activity

thresholding, Otsu method and an approach based onmathematicalmorphologicaltechnique.

These

approaches are applied to extract the RB of theMekong river within a 20 km long segment in theVMD for the years 2014 and 2019. The extracted RB
is then divided into 200 m long segments for eachapproach for both years. The surface change between
the two years is calculated for each of those segmentsin the VMD on RB erosion is analyzed.
REFERENCES
Chang Huang, Yun Chen, Shiqiang Zhang, and Jianping
Wu. Detecting, extracting, and monitoring surface
water from space using optical sensors: A review.
Reviews of Geophysics, 56(2)-333-360, 2018
Binh, D.V., Kantoush, S., Sumi, T. (2020): Changes tolong-term discharge and sediment loads in theVietnamese Mekong Delta caused by upstream dams,Geomorphology, Vol. 353, 107011.

Figure 1: Schematic illustration of the surface change analysis procedure for one segment. Green represents land,blue represents water. The background image is from 2014. The same MCP’s are manually selected in each data
set at location which are easy identifiable (f.ex. river mouth). Lseg = 200 meters.