Climate Change and Food Security- making the best use of rainfall and run off.

Think laterally..

The greatest challenge to farmers in semi-arid/ arid areas is how to make the best use of rainfall or run-off when it becomes available. Sometimes, we miss solutions to problems because they connect, in our mind, to solutions to problems that are diametrically opposite to the ones we face.... 

Consider then the following, for centuries, communities in areas prone to flooding have been avoiding the ravages of floods by controlling the movement of surplus water using “sandbags”. So widespread is the practice of filling small sacks with soil/ sand and placing them to prevent major catastrophes by:-

Stopping the swamping of sea-side towns by spring tides,

Stopping the overflow of major inland rivers and canals;

Directing the flow of flood-waters from any source away from city centres and power-stations; or simply by

Preventing run-off from entering private houses, shops and other public buildings;

that millions of small sacks are manufactured every year, to be distributed to communities vulnerable to floods throughout the world.These same small sacks that may be quickly filled and handled by either men, women or children have just as important a role to play in preventing the escape of water in dry areas by:- 

Holding rainfall in place where it falls by placing the bags in a line along a contour, or

Stopping sheet flow by placing the bags in a line along a contour- as before- to stop the flow and allow the water to infiltrate the soil,

Diverting streams and maybe even small river flows- to the place where the water will be most useful which may well be to olive-trees or vegetable plots in the foothills of the Pyrenees; or to sorghum plots in the Red Sea Hills of Sudan. 

The use of sandbags is recommended:-

1. Where stream size is small or a steady sheet flow is anticipated that could be diverted to gardens or fields;

2. In large-scale schemes with well-ordered head-works, where the main flows are controlled but where tertiary and in-field earth-bunds are vulnerable to breaches that must be rapidly plugged when they occur during the event to prevent water loss and erosion;

3. In schemes with cascading terraces where eroded bunds need increasing in height immediately to retain the required depth of water (0.5m);

4. All schemes where field entrance is through a single opening that should be closed quickly when the field is full and the flood is still flowing;

5. All schemes where gulleys appear after a single flood and need healing (isolating from further flows by stopping the water entering the head of the gulley);

6. All schemes where farmers wish to extend their growing areas rapidly by capturing an unexpected water harvest.

A guide as to how to use sandbags is given below. Further details may be obtained from < This e-mail address is being protected from spam bots, you need JavaScript enabled to view it >

A note on the use of sandbags for control of stream and sheet water flow.

Sandbags: small hessian or poly-weave sacks with a capacity of around 10kg

Sandbags are one of the most well- known devices for keeping floodwater under control. Types of floodwater that can be prevented, constrained or diverted with sandbags include:-

Holding rainfall in place by placing lines of sandbags end- to- end along contours;

Controlling sheet run-off from rains elsewhere by placing a single or double layer of sandbags end-to-end to contain or divert sheet run-off to preferential areas.

Diverting streams- creating new banks /bunds with pyramid placements for barriers more than 3 bags high.

Mending breaches in earth bunds (pyramid placement).

Overflowing rivers and streams- by strengthening and increasing the height of banks/bunds with layers of bags on top of existing banks/bunds.

Unfilled sandbags and a supply of sand or any soil that is available at the site is all you need to erect an effective barrier, as generations of experience in flood control have proven.

How to Fill and Position Sandbags

This is a two person job: one person holds the bag open and one person fills it.

Do not fill bags more than half full.

It is not necessary to tie the end of the bag.

Tuck the opened end under the filled half of the bag and position the bag with the tucked end pointing into the water flow.

Remove any debris from the area where the bags are to be placed.

For sheet flow control with single/double bag lines, place the half filled bags lengthways and not at right-angles to the direction of the water flow.

For more substantial barriers, place bags in layers like a brick wall.

Make sure that in the next layer each bag overlaps the one below by half.

Stamp bags firmly into place to eliminate gaps and create a tight seal.

Pyramid Placement Method

If you need to create sandbag structures more than three layers high you will need to build in a pyramid shape.For the structure to be stable, you should build the ‘sandbag wall’

three times as wide as you need it to be high

It will also be more effective if you alternate the layers lengthways and crosswise.

Tuck the loose end firmly under the filled portion of the bag

Stamp each bag in place.

WITH STRONG FLOWING STREAMS, DON’T BE GREEDY; DON’T TRY TO DIVERT THE WHOLE STREAM AND BUILD THE STRUCTURE in the shape of an arrow head ON THE INSIDE OF A BEND.