Why puddle pumps matter in flood defence
Puddle pumps are designed for situations where water levels are very low, or need to be pumped very low. In those conditions a standard submersible pump would either run briefly and burn out, or not work at all because the water is too shallow. The EVAK Residox 400 used here can pump water down to approximately 1mm, which makes it particularly effective for the residual water that accumulates behind flood barriers. For the background on this type of pump, see what is a puddle pump.
Manual vs automatic puddle pumps
Most puddle pumps are manual, turned on and off as required. This is deliberate, because manual operation allows the pump to reach extremely low levels. Automatic puddle pumps do exist, but they generally do not pump down as low. They are usually better suited to confined spaces such as lift shafts, chambers or sumps, where unattended operation is needed and a small standing water level is acceptable.
The site setup behind the flood barrier
In this case the EVAK Residox was deployed on a driveway behind a Water-Gate flood barrier. The barrier performed well and kept the bulk of the floodwater out of the property.
However, no flood defence is completely watertight. Seepage is inevitable, particularly at ground level and through joints, interfaces and the underlying ground, and that water needs managing or it accumulates on the dry side of the defence. This was a flash flood from a small stream, typically lasting no more than four hours. Because of the short duration, a portable puddle pump was the right solution. For longer events such as river flooding, a packaged pump station is often preferable, collecting water across a wider area and operating automatically on a float switch. In this flash flood the Residox could be placed exactly where water was pooling and moved as conditions changed, a major benefit of puddle pumps. It could also be used internally: where barriers are fitted at doorways, a puddle pump can sit inside and pump seepage back out, keeping internal levels to a minimum. This is exactly why flood barriers still need water pumps.
The role of pumps in flood defence schemes
Pumps are essential in any flood defence scheme. Without them, seepage, rainfall and groundwater all build up behind the defences. During longer events the hydraulic gradient becomes an issue: water tries to equalise, passing beneath flood wall foundations or rising through the ground, and active pumping is often the only way to manage it safely and stop levels rising behind the defence.
Hose selection and flow performance
Here the Residox was used with layflat hose. It worked, but as you can see the hose was prone to kinking, which reduced the pump's effective output.
To improve performance in future, either a suction and delivery hose could be used, or an elbow hose tail fitted. An elbow helps prevent sharp bends at the pump outlet and reduces friction losses. This has been advised for future deployments.
EVAK Residox 400 technical performance
The pump used here was the EVAK Residox 400. It has a 0.37 kW motor, a maximum head of 11 metres and a maximum flow rate of 205 litres per minute. The layflat hose introduced friction losses that reduced the achievable flow slightly, but even so the pump comfortably managed the residual water and kept the property dry. The EVAK Residox is an excellent choice for flood risk management where low-level water needs controlling: portable, able to pump very low, and robust in real-world flood defence. You can view the EVAK Residox puddle pump here, or compare it with our other picks in the Top 5 puddle pumps.
