EFFECT OF FLOOD PROTECTION DAMS IN THE RIVER FLOODPLAIN ON FLOOD ZONE SHAPE, FLOW VELOCITY FIELDS AND WATER LEVELS ON THE EXAMPLE OF A NUMERICAL MODEL OF THE KONDOMA RIVER

Abstract

The relevance of numerical modeling of flood zones, characteristics of flow velocity field and marks of the river water levels is caused by the necessities of engineering practical work in development of mineral deposits, which are often situated in extremely difficult hydrographic conditions. In such conditions, the standard methods for calculating the mentioned characteristics do not allow us to achieve the desired result or do not take into account the whole variety of processes occurring in open flows, which are able to significantly affect the safe and trouble-free operation of the designed constructions. The aim of the work is to show how the objects affect the change in the shape of the estimated flood zone, the flow velocity field, and water levels in conditions of constraining impact on the living cross-section of the flow during the passage of water rate of rare exceedance probability (1 % occurrence) on the example of the Kondoma river site and both existing and planned hydraulic constructions (flood control dams) and construction sites located in its floodplain. Methods. Numerical modeling of flow characteristics (estimated flood zone, distribution of speeds and directions of flow, estimated water levels) on the site of the Kondoma river was conducted using the HEC-RAS (Hydrologic Engineering Center – River Analysis System) modeling system ver. 5.0.5. The model comprised three different scenarios. Scenario 1, the floodplain is relatively unbroken and there are no flood control dams and overburden dump; Scenario 2, there is a current flood control dam and overburden dump in the floodplain; Scenario 3, there are all the current objects mentioned in Scenario 2 and a designed flood control dam in the floodplain. The studied characteristics of the Kondoma river on the site under investigation were compared within all three implemented scenarios. Results. A simulation model for the passage of flood (1 % of the exceedance probability) according to three scenarios was developed for the site of the Kondoma river, with Scenario 1 taken as the control. The model was calibrated, and the roughness coefficients of the floodplain and channel were chosen as adequate to actual conditions. Numerical flow characteristics were obtained (the shape of the estimated flood zone, the distribution of speeds and directions of flow, and water levels and depths) according to the three mentioned scenarios and the conclusions were drawn concerning the extent of influence of the current structures in the left floodplain of the Kondoma river on the shape of free surface, and also the influence under condition of a new flood control dam appearing in the left floodplain was forecasted.

Keywords

• flood protection dams
• numerical modeling
• flooded zones
• 2d hydraulic models
• simulation models
• hec-ras modeling system