Review official flood information

Check the latest Annual Flood Outlook, flood-risk maps, hydrological bulletins and warnings from NIHSA, NEMA and relevant state agencies. Use them to understand whether the wider local government area, river basin or community has known exposure.

Do not treat a broad regional forecast as a substitute for site-specific assessment. Two streets in the same neighbourhood can perform very differently because of elevation and drainage.

Inspect during or immediately after heavy rain

A dry-day visit shows appearance; a wet-day visit reveals performance. Observe how quickly water leaves the road, whether drains overflow, where runoff enters the site and whether neighbouring plots discharge water toward the property.

Where a rainy-day visit is impossible, request recent dated videos from multiple points and speak with independent residents.

Speak with neighbours, security staff and local businesses

Ask specific questions: How high did the last serious flood rise? How long did water remain? Which roads stayed open? Did water enter houses, compounds or septic systems? How frequently are drains cleared?

Do not rely only on the seller’s answer. Several independent accounts are more useful than one reassurance.

Compare the site elevation with the road and neighbouring land

A plot that sits below the road, drainage outlet or surrounding compounds may collect runoff. A raised site is not automatically safe either; filling can redirect water to weak points or settle if it was poorly compacted.

A topographical survey can establish levels and help a professional plan finished floor height, drainage falls and discharge points.

Trace the drainage route from beginning to end

Do not stop at the drain in front of the property. Find out where it leads. A neat roadside drain may discharge into a blocked culvert, undersized collector, closed channel or low-lying area that backs up during heavy rain.

Check whether drains are continuous, properly sloped, covered where necessary and free from buildings, refuse or vegetation.

Look for natural water paths and nearby water bodies

Identify streams, canals, wetlands, lagoons, rivers, swamps and low corridors. Even where a channel appears dry, the land may form part of a seasonal flow path.

NEMA’s public flood guidance advises against building in a floodplain unless the property is appropriately elevated and reinforced. Planning rules may also restrict construction on drainage channels, setbacks, buffer zones or flood-prone land.

Verify planning status and required setbacks

Ask your lawyer, surveyor and town planner to confirm that the property is not committed to a drainage channel, proposed road, waterway setback, buffer zone or other restricted use. For Lagos property, the state planning law contains strict provisions regarding structures on drainage paths, swamps and areas liable to flooding.

Never assume that an existing fence, building or allocation automatically proves planning compliance.

Obtain a proper survey and, where necessary, topographical data

A boundary survey identifies the land, while a topographical survey records levels, features, drains and contours. For larger developments or difficult sites, a drainage or hydrological assessment may be needed.

Investigate the soil and quality of filling

Soft, waterlogged or reclaimed ground may require specialist foundation design. Ask whether the plot was filled, what material was used, when filling occurred and whether it was compacted in controlled layers.

For construction, a geotechnical investigation should guide foundation and ground-improvement decisions rather than guesswork.

Check access and emergency routes

Inspect every practical route into the neighbourhood. A property may have a raised compound but still become isolated when a bridge, junction or low section of road floods. Consider access for residents, emergency services, school transport, deliveries and evacuation.

Estimate the full mitigation and maintenance cost

Possible costs include site filling, soil compaction, drainage construction, culverts, retaining walls, pumps, raised electrical equipment, waterproofing, erosion control and periodic drain cleaning.

Obtain professional estimates before purchase. Do not assume that “just add sand” is a complete engineering solution.

Review estate-wide responsibility

In a managed estate, ask who owns and maintains the drains, pumps, retention areas and access roads. Check the service charge budget, emergency plan, maintenance record and responsibility for major repairs.

A well-raised individual unit cannot compensate for a poorly maintained estate drainage system.