Why this matters now
“Half a month’s rain in a day” is becoming a familiar headline. Slow‑moving summer storms are dropping intense volumes over tight catchments; winters arrive on already saturated ground; and longer dry spells leave soils baked so that the first heavy rain simply runs off. The result? More surface water on the network, flash‑flooding in places far from mapped rivers, rising reactive costs and increased public complaints.
Traditional carriageway drainage still does essential work, but most urban and highway systems were designed around historic rainfall assumptions and steady conveyance. When rainfall intensity outruns pipe capacity – or when inlets are blocked, catchpits are already full, or outfalls are constrained – water finds its own path. Sustainable Drainage Systems (SuDS) help change those pathways. This is reflected in the Flood and Water Management Act 2010 (Schedule 3), which was developed to ensure new developments manage surface water sustainably, clarify who approves and maintains SuDS, and prevent uncontrolled connections that overload existing drainage networks.
How can SuDS help?
SuDS is less about “building a pond” and more about managing rainfall where it lands. By slowing runoff, creating places for temporary storage and letting water soak, filter or be released at controlled rates, SuDS reduce the burden on conventional drainage. Visible, surface‑based components also make water management legible to communities – a useful by‑product when explaining local flood risk.
Core outcomes: when SuDS are well planned and maintained:
Water quantity – lower peak flows into drains and watercourses.
Water quality – trap sediment, hydrocarbons and debris before discharge.
Amenity & understanding – green space that shows where water goes.
Biodiversity – habitat, shade and cooling in hard landscapes.
These blue‑green assets increasingly sit alongside statutory flood duties, active travel schemes and placemaking projects, giving authorities multiple returns from the same intervention.
Climate signals
Recent UK assessments and day‑to‑day operations point to three shifts that matter for drainage planning: heavier short‑duration bursts, wetter (on average) winters, and flashier summer downpours that arrive on either saturated or baked ground. Each push more water toward inlets faster than systems were designed for. Planning solely to historic records risks under‑designing today’s work and tomorrow’s budgets.
Authorities are already adapting. We’ve seen gully programmes brought forward ahead of forecast storms, roadside storage introduced where repeat ponding occurs, and natural flood management measures trialled to hold water back from vulnerable stretches. SuDS folds these strands into a joined‑up approach.
Why networks struggle in practice
Even well‑built drainage underperforms when inlet grates are leafed over, silt builds after repeated storms, downstream water levels back up, or impermeable areas silently expand through development and hardstanding. Under intense rainfall, those marginal losses translate to standing water, damaged surfacing causing potholes, and increased claims. Introducing staged storage or infiltration upstream protects downstream capacity and reduces emergency call‑outs.
Data first: understanding how water actually moves
Effective SuDS begin with evidence. Most authorities already hold valuable layers, but you can’t manage what you haven’t mapped. Before adding SuDS, authorities benefit from combining multiple data layers:
Asset data: Location, type, and condition of gullies, pipes, culverts, ditches, outfalls.
Ground levels & flow paths: LiDAR, digital terrain layers, surface water flow.
Connectivity: Which gullies actually drain where? Where do informal flow paths bypass the system?
Flood incident, complaints & standing water reports: Real‑world evidence of stress points and community feedback.
Land cover change: New hardstanding, development, compaction or tree loss affecting infiltration.
Targeting SuDS to these priority zones delivers the biggest return for limited budgets and strengthens funding bids.
Bringing it together
SuDS aren’t a replacement for drainage — they’re a way to support it. By slowing and spreading inflows, improving interception and creating controlled storage, authorities can extend the working range of existing assets, reduce reactive cleanses and build climate headroom into local networks.