Interface Model

Introduction

The interface model modifies the water surface elevations of flood plain grids and channel elements at specified time intervals (update intervals). There are three cases of interface situations: (1) channel overflow, (2) grid overflow, and (3) flooding of channel and grid elements.

Channel Overflow

When the channel is overflowing; the excess water is temporarily stored in the vertically extended space (figure 15b). Actually, it is the volume per unit length. This excess water is the product of the depth of water, width of the channel and length of the channel and is subsequently uniformly distributed over the grid elements. In other words, the new grid water surface elevation is equal to the old water surface elevation plus a depth of hw/L, and the channel water surface elevation now matches the parent grid water surface elevation.

Grid Overflow

When the water surface elevation of the grid element is greater than a specified surface detention (figure 15a), the excess water drains into the channel element and the new water surface elevation is changed according to the following two conditions (figure 15c), (a) if v > v', where v denotes the excess volume of water per unit length and v' denotes the available volume per unit length, the new water surface of the grid element is A= A - (v-v')/L and the new water surface elevation of the channel element is also equal to A; (b) if v < v', the new water surface elevation of the grid element is A = A- h and the new water surface elevation of the channel element is B = B + v/w.


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