Floods

Table of contents

Introduction

What causes floods?

Preparing for a Flood

Introduction

A flood is the very rapid covering with water of an area that is normally dry. Most flooding is caused by rainfall, and occasionally by storms, earthquakes, and rivers overflowing their banks.

The tremendous force and utter suddenness of floodwaters represent a real danger to both human and animal life (by drowning, after being trapped in an innocent-seeming flood wave). Rescue units throughout the world, using rubber dinghies and other special equipment, are often called on to help those trapped by floods.

Roads and buildings, too, are liable to extensive damage caused by flooding. Some roads are repaired yearly at the end of the flood season.

Studying floods and knowing their risk factors is very important.

In Israel, floods are a phenomena associated in particular with river beds and wadis in the Judean Wilderness and the Negev Desert.

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What causes floods?

A unique combination of climatic and geographical factors creates the right conditions for a flood to occur: heavy, continuous rainfall, ground that is impervious to drainage, a large catch basin for the stream water, and steep slopes leading to the catch basin.

That is to say, if rain is falling and the ground affords no drainage, the rain water stays on the surface. Small rivulets combine into small brooks; these combine into larger brooks and streams. At its source, near the watershed line, the flood looks like a stream coming out of nowhere. On a slope, the flood creates greater and greater streams and waterfalls. The force of the flood depends on the amount of rainfall and on the size of the catch basin. The more rain falls, the more water will flow. The larger the catch basin is, flows from more streams join in, and therefore the flow there is that much stronger. As stated above, flooding that is the result of natural disasters, capable of creating similar conditions, is also possible.

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Preparing for a Flood

Flooding, like earthquakes and fires, strike the home front without prior warning.

The main problem with forecasting a flood that occurs as the result of rainfall lies in the fact that there is no direct relationship between the area of rainfall and the flood area. It is enough that there is local rainfall in the Sinai Wilderness for Nahal Paran in southern Israel, to flood and cover the Arava road. Thus, for example, local rainfall and impervious ground cause water in small brooks related to the catch basin of Nahal Paran, which starts in Egypt, to mass. The water comes together, accumulates, and builds up great might. The steeper the slope, the more sudden and stunning is the flood wave that takes the Arava by surprise, an area that seems totally dry, without a cloud in the sky.

Cooperation between weather forecasting stations and high levels of inspection and analysis of the catch basins help to predict floods and to minimize the damage that such floods can bring in their wake. In order to prevent disasters from happening, civilian awareness is critical: listening to the media for directions, and following them to the letter.

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