A stormwater network is fine until it isn’t, and the gap between those two states is measured in minutes. Rainfall arrives without negotiation, capacity is fixed, and every pump, gate, and basin has to perform on demand or fail in public. When a stormwater system runs blind, the consequences write themselves.

Streets flood, basements back up, outfalls discharge over permit limits, and pumps fail at the worst possible hour. By the time a daily report shows what happened, regulators, residents, and lawyers are already involved. The KPIs below are the ones an operations leader should be watching live, not pulling out of a monthly summary.

Catchment Rainfall Intensity

• Why it Matters: Rainfall intensity drives every downstream decision. Knowing what’s hitting the ground now lets you stage pumps and clear storage before flow arrives.
• What it Measures: Real-time precipitation rate across catchment rain gauges, typically expressed as inches or millimeters per hour.
• What Happens if Missed: You react after the surge instead of before it. Pumps catch up rather than get ahead, and storage fills before gates can divert flow.
• Formula: Rainfall depth / time interval
• Indicator Type: Leading. Rainfall is the input that everything else in the system responds to.
• Unit of Measure: in/hr or mm/hr
• Ideal Visualization(s): KPI blocks, KPI trend with real-time alerts, GeoMap across rain gauges
• Frequency: Real-time (every 1 to 5 minutes)
• Data Required: Tipping bucket counts, rain gauge timestamps, gauge location, intensity thresholds
• Pro Tip: Set tiered alerts on intensity, not just total volume. A half-inch in ten minutes hits the system harder than two inches over four hours.
• Red Flag: Intensity climbing on multiple gauges simultaneously while pump stations are still in dry-weather mode.

Pump Station Wet Well Level

• Why it Matters: Wet well level is the heartbeat of every lift station. It tells you if pumping is keeping up with inflow, second by second.
• What it Measures: Real-time water depth in each lift station wet well, measured against high and low alarm setpoints.
• What Happens if Missed: Levels climb past overflow setpoints and you find out from the public, not your control room.
• Formula: N/A (direct measurement)
• Indicator Type: Current. Reflects the active hydraulic balance between inflow and pumping capacity.
• Unit of Measure: ft or m
• Ideal Visualization(s): KPI blocks, KPI trend with real-time alerts, Pareto chart when ranking stations by deviation from setpoint
• Frequency: Real-time (every 30 seconds to 1 minute)
• Data Required: Wet well level transducer readings, high and low alarm setpoints, pump run status
• Pro Tip: Watch the slope of the level curve, not just the absolute height. A flat-then-rising trace during a storm usually means a pump just dropped out.
• Red Flag: Level rising while every pump shows running. Either a check valve has failed and a pump is coasting, or inflow has overrun installed capacity.

CSO Activation Frequency and Volume

• Why it Matters: Combined sewer overflows are the most regulated event in your system. Volume and duration drive permit standing, public notification timelines, and consent decree obligations.
• What it Measures: Number of overflow events at each CSO outfall and total volume discharged per event, per year.
• What Happens if Missed: Late or inaccurate reporting becomes a compliance issue before it becomes an operational one. Penalties stack quickly.
• Formula: Σ (Discharge flow × duration) per outfall per event
• Indicator Type: Lagging. The event has to occur before it can be tallied, but real-time detection still drives response and notification.
• Unit of Measure: count and gallons (or m³)
• Ideal Visualization(s): KPI blocks, Bar chart by outfall, Pareto chart when ranking outfalls by volume, Tables for regulatory reporting
• Frequency: Real-time during events, daily and monthly aggregates
• Data Required: Outfall flow measurement, level above weir crest, activation duration, event start and end timestamps
• Pro Tip: Tie every CSO activation to the upstream rainfall record automatically. Auditors will ask for that pairing every time.
• Red Flag: Frequent low-volume activations from the same outfall during minor rain events. That points to upstream blockage or an undersized control structure.

Detention Storage Available

• Why it Matters: Available storage is the buffer between inflow and discharge. It tells you how much rain the system can absorb before the network surcharges.
• What it Measures: Remaining volume in each detention or retention basin relative to its full design storage capacity.
• What Happens if Missed: Operations enters a storm with less buffer than expected and runs out of storage mid-event.
• Formula: (Max storage – Current storage) / Max storage × 100
• Indicator Type: Current. Reflects the immediate buffering capacity of each basin.
• Unit of Measure: % or ft³ (m³)
• Ideal Visualization(s): KPI blocks, Bullet chart against design capacity, KPI trend with real-time alerts, Pareto chart when ranking basins by remaining capacity
• Frequency: Real-time (every 1 to 5 minutes)
• Data Required: Basin level, basin stage-storage curve, design max storage, outflow rate
• Pro Tip: Pre-storm drawdown is free capacity. Use forecast intensity to lower basin levels before the cell arrives.
• Red Flag: Basin sitting above seasonal average level during dry weather. Outlet structure may be partially obstructed.

Sewer Surcharge Events

• Why it Matters: Surcharge means pipes are running full and pressurized. Once surcharge reaches a manhole, you’re minutes from street flooding and basement backups.
• What it Measures: Count and duration of events where the hydraulic grade line in a pipe exceeds the pipe crown elevation, by location.
• What Happens if Missed: The first sign of trouble is water in basements or geysering manhole covers, not a screen alert.
• Formula: Σ (Time HGL > pipe crown) per location per event
• Indicator Type: Current. Surcharge happens in real time and resolves once flow drops back below pipe capacity.
• Unit of Measure: count and minutes
• Ideal Visualization(s): KPI blocks, Status history trends, Pareto chart when ranking pipe segments by surcharge duration, GeoMap across the network
• Frequency: Real-time (every 1 minute)
• Data Required: Pipe pressure and level sensors, pipe crown elevation, manhole rim elevation
• Pro Tip: Track the lead time between rainfall peak and surcharge onset for each subbasin. That number is your operational window for proactive control.
• Red Flag: Surcharge appearing in segments that didn’t surcharge during similar past storms. Usually a downstream constriction or new I/I source.

Outfall Turbidity at Discharge

• Why it Matters: Turbidity is the most visible and most cited water quality parameter. Spikes at outfalls land directly on permit reports and public complaints.
• What it Measures: Real-time turbidity at MS4 or treatment outfalls, typically reported in NTU at the point of discharge.
• What Happens if Missed: Discharge events exceed permit limits without operations knowing until the lab pulls the next grab sample.
• Formula: N/A (direct sensor reading)
• Indicator Type: Current. Reflects in-stream water quality at the moment of measurement.
• Unit of Measure: NTU
• Ideal Visualization(s): KPI blocks, KPI trend with real-time alerts, SPC trend (control chart), Pareto chart when ranking outfalls by exceedance count
• Frequency: Real-time (every 5 to 15 minutes)
• Data Required: Turbidity sensor readings, outfall flow, permit thresholds, sensor calibration timestamps
• Pro Tip: Pair turbidity with flow. High NTU at low flow means a sediment source upstream, not just first-flush wash-off from the storm.
• Red Flag: Turbidity stays elevated long after rainfall stops. A construction site discharge or illicit connection is likely contributing.

Pump Cycling Frequency

• Why it Matters: Excessive starts and stops are the leading cause of pump failure. High cycle counts predict motor and check valve problems before runtime reports show any wear.
• What it Measures: Number of pump start events per hour or per day, calculated for each pump in each station.
• What Happens if Missed: Pumps fail mid-storm because a small part wore out weeks earlier and nobody flagged the cycling pattern that predicted it.
• Formula: Σ (Pump starts) / time interval
• Indicator Type: Leading. Cycling patterns predict mechanical failure days or weeks ahead of breakdown.
• Unit of Measure: starts/hour or starts/day
• Ideal Visualization(s): KPI blocks, Histogram of cycle counts, Pareto chart when ranking pumps by cycles, Status history trends
• Frequency: Real-time, rolled up hourly and daily
• Data Required: Pump run and stop status, timestamps, runtime hours
• Pro Tip: Rapid cycling during dry weather usually means the float or level controls are misaligned, not that demand is high.
• Red Flag: Cycling rate doubling on a single pump while its lead and lag partner runs normally. That pump is doing more work and will fail first.

Pump Specific Energy

• Why it Matters: Pumping is the largest controllable energy cost in stormwater operations. Specific energy reveals which stations and which pumps deserve attention first.
• What it Measures: Energy consumed per unit volume pumped, calculated per pump or per station over a defined time window.
• What Happens if Missed: Inefficient pumps run quietly for years, spending budget that could fund the next station rehab project.
• Formula: kWh consumed / volume pumped (MG or m³)
• Indicator Type: Lagging. Reflects performance over a completed pumping period rather than live operation.
• Unit of Measure: kWh/MG or kWh/m³
• Ideal Visualization(s): KPI blocks, Bar chart by station, Pareto chart when ranking pumps by specific energy, KPI trend with real-time alerts
• Frequency: Hourly aggregation, daily and monthly rollups
• Data Required: Pump motor power draw, flow rate per pump, runtime hours
• Pro Tip: Compare specific energy across pumps in the same station. The outlier almost always traces to wear on the impeller or a partially closed isolation valve.
• Red Flag: Specific energy creeping upward month over month at a station with no flow change. Mechanical degradation is in progress.

Infiltration and Inflow Rate

• Why it Matters: Every gallon of groundwater or rainwater entering the sanitary side is one less gallon of capacity available for actual sewage during a storm.
• What it Measures: Excess flow above dry-weather baseline attributable to groundwater infiltration and rainfall-derived inflow into the collection system.
• What Happens if Missed: Treatment plants accept the cost, overflows accept the consequences, and source defects keep growing year over year.
• Formula: Wet weather flow – Dry weather baseline flow
• Indicator Type: Lagging. Calculated after a wet weather event by comparing flow against the established baseline.
• Unit of Measure: MGD or m³/day
• Ideal Visualization(s): KPI blocks, Bar chart by subbasin, Pareto chart when ranking subbasins by I/I contribution, XY/scatter plot of rainfall vs I/I response
• Frequency: Calculated per storm event, rolled up monthly
• Data Required: Flow at subbasin meters, dry-weather diurnal baseline, rainfall depth, groundwater elevation
• Pro Tip: Plot I/I against antecedent moisture for each subbasin. Steep slopes point to inflow defects, while flat slopes with high baselines point to infiltration defects.
• Red Flag: Subbasin I/I response getting worse across consecutive seasons. Pipe condition is deteriorating faster than rehab is keeping up.

Detention Basin Drawdown Time

• Why it Matters: A basin that drains slowly isn’t ready for the next storm. Drawdown time tells you when the system is back to standby.
• What it Measures: Time required for a detention basin to return from peak storage to its dry-weather operating level after a storm.
• What Happens if Missed: Back-to-back storms hit a basin still partially full, and outlet controls can’t open fast enough to prevent surcharge.
• Formula: t(level = operating baseline) – t(level = peak)
• Indicator Type: Lagging. Measured along the recession limb of each storm event after the peak passes.
• Unit of Measure: hours
• Ideal Visualization(s): KPI blocks, KPI trend with real-time alerts, Bar chart by basin, Pareto chart when ranking basins by drawdown time
• Frequency: Calculated per storm event
• Data Required: Basin level over time, event start and end timestamps, outlet flow rate
• Pro Tip: Compare drawdown across similar storms over the season. A growing drawdown time means the outlet is fouling.
• Red Flag: Drawdown extending past design parameters with no upstream changes. The outlet orifice or flap gate is likely partially blocked.

Why Real-Time Visibility Matters

Stormwater operations live or die by what happens in the first thirty minutes of a storm. By the time a daily report shows a pump cycled too often or an outfall ran turbid for an hour, the regulatory clock has already started and the public has already noticed. Real-time visibility flips that timeline. Operators see rainfall climbing, storage filling, and pumps responding while the system can still be steered.

Operating blind in stormwater is expensive in ways that don’t show up on a single line item. CSO penalties, basement backup claims, emergency overtime, and accelerated pump rehabs all trace back to decisions that arrived a few minutes too late. Continuous KPIs across rainfall, hydraulic state, water quality, and asset performance give operations leaders the lead time and the evidence to act before those costs compound.

How Transpara Can Help

If real-time operational visibility is a challenge you’re facing, you’re not alone. At Transpara, we help teams like yours gain clarity from complex systems without the need to centralize or overhaul your data stack.
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