The dam slope stability under the transient condition during an extreme flood

Svitlana Velychko,Olena Dupliak,S Semerikov,S Chukharev,H Danylchuk,P Nechypurenko,V Osadchyi,S Klimov,O Bondarenko,A Striuk,T Vakaliuk,S Sakhno,A Iatsyshyn

doi:10.1051/e3sconf/202128010010

Abstract

Mountain Flood Control Reservoir (MFC Reservoir) is used to reduce the flood level in the mountainous area and protect settlements downstream. The special feature of this MFC Reservoir is the fast filling during 1-2 days, short storage time at the maximum level and speed falling of the water level. Simulation of the MFC Reservoir operation was carried out on the software Midas GTS NX. Two rockfill dam models were developed: with the core and with the screen. The fluctuation of the water level in the MFC Reservoir was taken as the transformed flood from 1% to 10% probability. The fast water level change in the MCF Reservoir creates the transient seepage condition during the flood. During the water level rising in the MFC Reservoir, the upstream slope stability gradually increases because of hydrostatic pressure. After the water level begins to fall with rate of 0.7 m/hour, the slope stability decreases. The core or screen location significantly affects the stability of the upstream dam slope. The simulation showed that the upstream slope of the dam with the core was more stable. Due to the high hydraulic conductivity, the upstream dam prism with the berm significantly dampens the pore pressure in the dam and increases the stability of the upstream slope.

Highlights

The floods take place both in winter and in the warm period, but cold floods have the higher flow rates in the Transcarpathian region
The direction of water movement changes: part of the water continues to seep through the downstream slope, as evidenced by the gradual increase in water level inside downstream prism and approaching the steady state position, the second part changes direction to the upstream slope
Two different type of the impermeable layer of the dam were used for simulation: the dam with core and the dam with screen

Summary

Introduction

The floods take place both in winter and in the warm period, but cold floods have the higher flow rates in the Transcarpathian region. Due to the unstable temperature regime in winter, the frequent thaws are observed in the Tisza river basin, during which extreme cold floods are formed. In the mountainous part of the Tisza river basin floods have the high flow rate and short lag time, due to steep floodplain slopes and riverbed slope, the duration of flood does not exceed 3-5 days. One of the active flood protection measure to lower water levels is using Mountain Flood Control Reservoir, which transforms the extreme flood flow of 1% probability to safe one. Mountain Flood Control Reservoir is created by dam with the bottom spillway. In the case of the extreme flood, the part of the river runoff that exceeded the Channelforming flow is temporarily accumulated in the MFC Reservoir formed by the dam [2]. To save vegetation diversity inside the MFC Reservoir area, the duration of the water storage in the MFC Reservoir should not exceed 8-10 days, during which the water gradually flows downstream

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