Pumping water from the basement: how to deal with flooding at home with groundwater

Recommendation points

• Working with the basement floor
• How to equip a catchment pit
• Choosing a pump for pumping
• How and which pipe to lay
• Where to dump water

If the basement is periodically flooded, and it is not possible to solve the problem at the root, you need to at least organize the pumping of water and its discharge. Therefore, we propose to get acquainted with the technique of draining basements and the equipment used for this..

Working with the basement floor

The constant presence of water in the basement is not only a harm to the supporting structure and internal equipment. First, you need to solve the problem of practicality: remove dirt and facilitate the rapid flow of water to a certain common point, from which it will be removed. It is advisable to carry out all work during the period of the greatest drop in the groundwater level: in a summer drought or in winter, if the basement is warm.

First, you need to deepen the basement floor. Ideally, in order to reduce the harmful effect of water on the walls, it is necessary to deepen below the level of their occurrence by 25-30 cm. The floor must be planned in a special way, creating the correct slope. Even small changes in level can cause water retention, which can cause dampness and a smell of musty water in the basement..

It is easier to place the lower point for all slopes in the corner of the basement or closer to its center if the floor area exceeds 20 m². It is advisable to adhere to the length along the fall of the inclined section of no more than 5–6 m. The lines of convergence of the slopes are almost always located diagonally. Steel pipes are placed on them, used in the manner of beacons as when pouring a screed.

1. Pit. 2. Clay lock over the entire floor surface with a slope towards the pit. 3. Gutters. 4. Foundation of the house

The planned floor should ultimately be a hydraulic lock made of soaked and carefully tamped clay. Even if sandy loam has already started at the existing depth, there should be a layer of clay 15–20 cm, otherwise the deposition of sedimentary particles along with water will be pronounced. When installing a castle 30–40 cm from the walls, the floor rises sharply at an angle of 30–35 °, forming a kind of doorways, the height of which is 3–5 cm below the zero mark.

A particularly difficult case is basements with a monolithic concrete floor that has lost the integrity of the waterproofing. Slopes in this case are formed at the existing level using a preparatory screed. It is very important to ensure its high-quality adhesion to the main body, therefore, often the concrete floor has to be thoroughly cleaned and special modifiers used to improve adhesion.

In both cases, in order to make the floor suitable for walking, it is necessary to lay on it a hygroscopic bedding of 20-25 cm of fine gravel or knock down gangways. To avoid subsidence of gravel through the clay floor, it must be covered with a layer of geotextile. It is important to additionally protect the walls from high humidity, for which you can use moisture-resistant plaster or “liquid glass”.

How to equip a catchment pit

At the point of descent of the slopes, a pit is arranged in which the flowing water will be collected. It has one more purpose: in deep basements, a wide, recessed “well” helps to eliminate excess groundwater pressure and the associated floor swelling..

The pit does not have to be arranged before pouring the substrate, it is enough to knock down the panel formwork in advance in a square with a side of about 80 cm. A small depression is dug in this shape. The total volume of the pit should be 0.5 m³ or more if water is supplied actively.

The working part of the header is represented by the casing. Its diameter should allow the installation of a float drainage pump for pumping water, approximately 350-400 mm. The pipe can be either steel or asbestos-cement or polyethylene – there is no fundamental difference. In the walls, in a checkerboard pattern, holes with a diameter of 12-14 mm must be drilled with a distance of about 25 cm between them. Before installation, it is recommended to wrap the pipe with several layers of plastic mesh with a mesh of up to 5 mm.

1. HDPE pipe. 2. Pit. 3. Drainage pump. 4. Drainage pipe. 5. Gravel bedding

The bottom of the casing pipe is deaf, it can be either welded or concreted with a layer of about 7–8 cm. After installing the pipe, the formwork is removed, and the remaining space in the pit is covered with the same rubble that was used to fill the floor. Install the casing so that the upper edge comes out flush with the zero floor mark. For ease of passage, the water intake is covered with a removable welded mesh made of reinforcement.

In a concrete floor, the pit must be arranged in such a way that the horizontal insulation of the floor is not disturbed. The easiest way when pouring is to use a 20-kilogram bucket from building mixtures, which is temporarily filled with water and rubble from floating up. If there was no pit in the basement, part of the floor should be disassembled and a sump should be cast using modified concrete with low water absorption.

Choosing a pump for pumping

Most submersible slurry pumps are suitable for pumping water. Performance is of key importance: it must be large enough to cope with the volume of incoming water, at the same time, an unnecessarily powerful pump will operate in intermittent mode, which will affect the durability of the contact group and the motor.

The height of the head should be appropriate for your site and the prepared water discharge field. Usually, a lifting height of 10-12 m is quite sufficient, but you always need to make a small margin of power in case the drain pipe is not straight or has a long length..

The ingress of all kinds of debris into the pump cannot be ruled out, although with the correct arrangement of the casing, this will have a minimum value. The pump should be capable of pumping sand slurry with a fraction of up to 3-5 mm, the specific size depends on the mesh used for the casing filter.

How and which pipe to lay

For water drainage, it is desirable to use pipes with the lowest hydrodynamic resistance. For pumping contaminated water, HDPE pipes with smooth walls and the possibility of an extended laying without connections are optimal. Diameter must match the pump connection.

In the area closest to the pump, the pipe should be lifted to approximately the discharge level, that is, the first pipe segment is mounted as vertically and without kinks as possible. The outlet of the pipe from the basement must be done in the nearest wall by digging from the back side. The passage is carefully sealed with cement mortar, the damaged waterproofing is restored.

The HDPE pipe can be laid without a special prepared bed and even above the freezing depth, if a slope of at least 1000: 5 is provided. It is recommended, however, not to lay the pipe unprotected in rocky ground and open on the surface..

Where to dump water

The place for discharging the pumped out water is selected based on the volume of pumped out and the intensity of flooding. For short seasonal floods, the method of water discharge into / onto the soil with the device of the simplest filtration field is quite suitable. The trench in which the perforated section of the pipe is laid must be deepened and covered with large road rubble and sand, alternating layers with non-woven geotextiles. On average, for one cubic meter of discharged water, the length of the trench should be 6–8 m.

A more voluminous discharge requires the laying of its own channel to the nearest melioration or drainage trench. A limited amount of water can also be received by a self-equipped filter well. Do not forget that with a year-round flow of water into the basement, its continuous pumping is not the best option for disposal. An intense flow of moisture in the soil leads to its erosion, which affects both the relief and the reliability of buildings on a shallow foundation.