What storm water and flood management covers
Storm water work deals with where water goes during and after rainfall: how it is collected on a site, how it is conveyed away, and what happens downstream as a result. Flood management deals with the other side of the same problem — establishing which parts of a site are at risk from an existing watercourse, and what may and may not be built there.
Both are treated together because a development that solves its own drainage by pushing the problem downstream will not be approved, and should not be built.
Typical deliverables
- Storm water management plans — the overall drainage strategy for a site, including attenuation where post-development runoff must be limited to pre-development rates.
- Drainage system design — pipes, inlets, channels, culverts and outfall structures sized for the design storm.
- Flood line determination — hydrological and hydraulic analysis establishing flood lines along a watercourse, for planning applications and for setting safe development setbacks.
- Attenuation and detention facilities — sizing and detailed design of ponds and other storage.
- Earth dam analysis and design — structural and hydraulic assessment of embankment structures, including spillway capacity.
When you need it
Flood line determination is usually required where a site falls near a river, stream or drainage channel, and authorities will ask for it before approving a layout. Storm water design is required on essentially every development that changes the amount of hard surface on a site, which is nearly all of them.
It is also worth commissioning this work when an existing property floods, ponds, or discharges onto a neighbour, since the fix is frequently a modest change to levels or an additional outfall rather than a wholesale rebuild.
How we work
Analysis starts from catchment characteristics and rainfall data, with the site levels confirmed by topographical survey. From there we model the runoff, size the system to the agreed design storm, and check the downstream condition before and after development. Where attenuation is needed, we design it to release at a rate the downstream system can actually accept.
The output feeds directly into the civil drawings and, where the work goes to site, into construction supervision so that what was designed is what gets built — with drainage in particular, small deviations in level during construction have outsized consequences.