Living by the sea means keeping one eye on the tide tables and the other on the weather forecast. When a sudden tidal surge or a combination of high tide and heavy rain threatens, sandbags remain one of the simplest and most effective ways to keep water out of doorways, garages and outbuildings. They are not a permanent flood defence, but used correctly they can buy you valuable time and reduce damage.

Understanding What Sandbags Can and Cannot Do

Sandbags are a temporary measure. They work by diverting shallow, slow-moving water and by absorbing some of the impact. They cannot hold back deep or fast-flowing water, and water will rise above them. For a typical doorway, a barrier two or three courses high — around 30 to 45 centimetres — is usually enough for a sudden tidal flood. Sandbags also work best when combined with heavy-duty plastic sheeting. The sheet goes against the door or wall, and the sandbags hold it in place, creating a continuous seal that stops water seeping through gaps.

Choosing and Filling Your Sandbags

Hessian sandbags are traditional and biodegradable, but they rot if left wet. Polypropylene bags are lighter, stronger and last longer. Whichever you choose, fill them correctly:

• Use builder's sand, sharp sand or soil free from stones and debris.
• Fill each bag about half to two-thirds full. Too full, and it will not mould to the next bag; too empty, and it will not hold its shape.
• Aim for 15 to 20 kilograms — heavy enough to stay put, light enough to lift.
• Fold the open end over and tuck it under, or tie it with string, so the fill does not spill.
• Prepare more bags than you think you need; spares are better than shortages.

Safe Stacking Methods for Doorways

The way you stack matters as much as the bags themselves. Follow these steps for a doorway barrier:

• Clear the area of mats and anything sharp.
• Lay heavy-duty polythene across the doorway, up the door and out 30 centimetres each side.
• Place the first course flat, lengthways, tight against the door, overlapping ends by half a bag.
• Stagger the second course so each bag sits over the join below — brick bonding prevents a weak straight line.
• Tamp each bag down with your foot or a mallet for a firm, compacted layer.
• Build to the height you need: two courses (30 cm) for most tidal flooding, three (45 cm) for extra security. Never go higher than three courses unless braced, as the weight can push the door inwards.
• Fold the top of the plastic sheet over the final course and secure with a sandbag to stop water running behind.

Protecting Outbuildings, Garages and Air Bricks

Outbuildings often have lower thresholds than the main house, so they need attention early. For a garage door, build a sandbag wall across the full width, using the same brick-bond method. For up-and-over doors, place bags against the frame too. Air bricks and vents are a common weak point. Do not block them permanently, as your building needs ventilation, but for a flood event you can cover them with a plastic sheet and a single row of sandbags. Remove the covering as soon as the water recedes. A single course around a shed base stops water seeping under the floor. If you have a low window or a cellar light, treat it like a doorway: plastic sheet first, then sandbags.

Removal, Drying and Storage

Once the floodwater has gone down, do not leave sandbags in place. Damp bags against a wall can cause rot. Remove them carefully:

• Wear gloves and, if the sandbags have been in floodwater, a dust mask. Floodwater can contain sewage and contaminants.
• Lift bags with your legs, not your back. Get help for heavy bags.
• Dispose of sand that has been in contact with floodwater at a council waste site. Do not spread it on your garden or use it in play areas.
• Hessian bags can be washed, dried thoroughly and reused if intact. Polypropylene bags can be hosed down and dried. Throw away any torn or mouldy ones.
• Store dry sandbags flat in a dry shed or garage. Keep empty bags and a few filled ones ready for the next warning.

Before the Next High Tide: A Quick Checklist

Keep a flood kit ready: empty sandbags, a supply of sand or soil, heavy-duty plastic sheeting, gloves, a mallet and a torch. Check your tide tables and sign up for flood warnings from your local council or the national flood service. Know where your door thresholds and air bricks are, and practise a dry run so that you are not learning on the job in the dark and rain. Coastal living is a joy, and a little preparation means you can enjoy it with confidence, whatever the tide brings.