There is no reason why you should need anything more than sandbags to protect your property, they work perfectly as flood barriers for doors. The people who still suffer from water ingress when using sandbags as a flood protection measure are the ones that haven’t used them properly.
The one thing that people forget to do is to purchase a piece of plastic sheeting to put in place before they lay the sandbags. That way, if a little water still gets through the sandbags, the plastic sheeting will be there to catch it. Attach the plastic sheeting to the wall surrounding the door and fix in place with some tape.
Build your sandbag wall the same as you would build a brick wall with an overlap bond. You will then fold the plastic sheeting over the second to last layer of sandbags.
Make sure that you have enough sandbags to be able to cover the job, if you need to build anything that is more than three layers of sandbags high, then you’ll have to build a pyramid style wall the same as below.
After each sandbag is laid, make sure you stamp them in place to get rid of any gaps that water could potentially penetrate.
If you lay the sandbags as they are intended to be used, they will stop water. Just make sure you take a look at the diagrams before you start and you shouldn’t have any problems.