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MODELING OF FLOODPLAIN INUNDATION PROCESS
IN LOW-LYING AREAS
PHAM THANH HAI
∗
, TAKAO MASUMOTO and KATSUYUKI SHIMIZU
National Institute for Rural Engineering
2-1-6 Kan-nondai, Tsukuba, Ibaraki, Japan
∗
thanhhai@nkk.affrc.go.jp
A simulation model, which covers floodplains of the Mekong River from Kratie
in Cambodia to near the Vietnamese border, was developed by using a finite ele-
ment method with two-dimensional (2D) shallow-water equations. The model
was applied to typical flows of the years 2000 and 2003 (as representative of
recent large flood and drought years, respectively) in the river and floodplain
systems. Refined, unstructured, triangular FEM meshes were generated for
the study area. Main roads, dikes, colmatages, and waterway-opening works,
which may have some influence on flow-regimes, were taken into account in
the simulation. Moving boundary problem was treated by applying a threshold
technique in which nodes having a thin water depth are reset to dry ones in all
moving boundary elements every time. Finally, simulated results and observed
water-levels and discharges at available gauges were compared to verify the
model simulation.
1. Introduction
The existence of reverse flow into Tonle Sap Lake from the Mekong River
is a unique feature of the flow in and around the lake and its environs
in the Mekong River system. This phenomenon occurs annually; that is,
in May/June, the water from the main Mekong River flows down to the
lower Mekong and Bassac rivers, and at the same time flows upstream into
Tonle Sap Lake. In September/October, when the water level of Tonle Sap
Lake is higher than that of the Mekong River, this stored water starts to
drain into the lower Mekong and Bassac rivers.
1
The purpose of this paper
is to develop a two-dimensional FEM simulation model and to examine
this unique feature of flooding processes using full terms of depth-averaged
shallow water motion equations. Such models are capable of addressing
the geometric complexity usually found in topography as well as at the
boundaries of the study area.
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