Detention volume is not determined by hydrology alone.
It is governed by how inflow is managed against discharge over time.
Why Adaptive Discharge Matters
Detention volume is governed by discharge behavior.Static outlet structures concentrate control near design head and cannot respond to variability in storm intensity or antecedent conditions.
Conventional outlet controls are defined by a fixed Q–H relationship.
Traditional controls are defined by a monotonic Q = f(H) relationship—flow increases with head. Reaching the design condition requires increasing water level, which constrains system performance to conditions near the design head. This constrains system performance to conditions near the design head.
Automated outlet systems introduce logic-based discharge shaping, allowing flow to be managed across a broader operating range — not just at peak design elevation.
Expanding control beyond the Q–H relationship allows storage to be used more efficiently.
Cost savings in the range of 5%–30% are commonly achieved compared to passive outlet controls. Automated Outlet Structures (AOS) measure rainfall and water level in real time and adjust discharge to match the evolving storm hydrograph.
This expands the hydraulic performance envelope of the detention system and can meaningfully reduce required storage volume in both retrofit and new development applications.
Impact on Detention Design
Expanding discharge control directly impacts:
- Footprint
- Depth
- Volume
- Hydrology
The result being the AOS can meaningfully reduce the cost of site development in the early stages of the design process, allowing the design engineer to offer their clients more options in their land development plans.
How the Automated Outlet Structure (AOS) Works
The AOS integrates level sensing, telemetry, and logic-based actuation to manage discharge in real time.
Core System Architecture
- Level sensors (ultrasonic)
- AOS rain gauge (tipping bucket 1 min. 0.01″resolution )
- Remote telemetry, weather forecast and control interface optional
- Local default logic and remote updating in real time if needed
- Actuated gate position
Typical Workflow
- Monitor rainfall and water level
- Predict required detention and release timing
- Adjust gate position to maintain optimal outflow
- Log performance data for reporting and optimization
The AOS uses multiple inputs and logic to make informed flow control selections. The AOS is measuring water level and rainfall. It’s actually calculating the current storm hydrograph every minute. It compares the current rainfall at that time, to the design storm hydrographs, as the rain accumulates eventually the current hydrograph matches the design hydrograph, the AOS knows exactly what must be released for this event, regardless of the current water level. Q ≠ f(H). The AOS can set the gate position to achieve the release rate for the current storm, not water level.
These data-driven systems allow municipalities and engineers to retrofit existing basins or design smaller new ones that respond to actual conditions rather than assumptions, improving both hydraulic efficiency and lifecycle value.
Case Studies
New Development Optimization
In a new commercial development, adaptive outlet strategy reduced required detention volume by approximately 30%, reducing excavation depth while maintaining downstream discharge targets
Featured Project: District 31 – Alabaster, AL
The District 31 retrofit replaced conventional outlets in three existing ponds with automated outlet structures (AOS).
By dynamically matching real rainfall and storage conditions, the retrofit improved discharge timing, reduced peak water surface elevations, and enhanced post-storm drawdown efficiency—without expanding pond footprints.
