Pit volumes, pump sizing, and alarms.
Size equipment pits and sumps to avoid water ingress around automatic HVM bollards. Enter inflow assumptions, groundwater levels, and discharge paths (334, 245, 616) to get storage/throughput recommendations with debris and maintenance allowances. Outputs slot into drawings and method statements (931, 721) and help satisfy authority reviewers for wet sites (717, 423). Include one-sentence context that naturally links upward to the parent hubs (this section and the chapter hub). Add SIRA context with a link to SIRA Bollards (UAE) when relevant. Link installation pages only if helpful: What to Expect and Installation Guide.
Important: This is a general guide. For live projects we develop a tailored
Method Statement & Risk Assessment (MS/RA) and align with authority approvals (e.g., SIRA) where in scope.
927.1 Purpose
Right-size pits/sumps for sockets, HPUs, and enclosures around HVM bollards (245, 616, 334).
Correctly sized pits protect controls and HPUs from flooding and silt, preserving reliability and rating intent. In wet or tidal locations, a sump also manages groundwater effects that can force water into ducts and sockets. This page explains inputs, a transparent sizing method, and outputs that drop into drawings/specs and reviewer packs.
Use this alongside 334 Drainage, the site drainage strategy at 245, and pit construction guidance at 616 to keep design, installation and approvals coherent.
| Aspect | What matters | Where to verify |
|---|---|---|
| Performance | Whole system (bollard + footing + drainage) | 410 Global crash ratings |
| Operations | Duty cycles, fail-state, safety devices & measures | Installation hub |
927.2 Inputs
Inflow rates, groundwater, rainfall, solids load, discharge options (423, 616). Crash rated bollard pits included.
Start with credible inflows: (a) rain ingress via covers/slots, (b) wash-down water, and (c) seepage from seasonal high water tables. Note debris/silt loading based on site use (events, landscaping). Confirm discharge routes—gravity to storm line/soakaway or pumped to an approved point. For saturated sites, add a freeboard margin and check 423 groundwater/soil effects.
Authority contexts (Dubai/SIRA) often require evidence of non-contamination (e.g., oil interceptors for vehicle areas) and backflow protection. Pair this with SIRA expectations (UAE) and the construction-stage guidance in 616 pits/sumps.
927.3 Method
Volume, retention time, pump duty/backup, alarms (616, 517). Includes silt allowance.
(a) Volume: size the wet well for peak inflow, silt settlement, and maintenance access. Include a silt pocket and a silt basket where frequent debris is expected. (b) Retention time: aim for short on-plateau residence to minimize odors and silt deposition; the basket/pocket takes the solids load, not the whole sump.
(c) Pump duty: select a duty or duty/assist set so the operating point matches the pump curve at the total dynamic head (static lift + friction). Provide non-return on discharge and a backflow preventer (NRV). (d) Alarms: set level switches for run, standby, and high-level alarm; add a “pump fail” alarm and an external beacon if flooding would impair automatic bollard operation. Cross-check energy/power assumptions with 517 Energy Budget.
927.4 Outputs
Pit size, pump spec hints, alarm setpoints, backflow notes (616.3–616.5). Buildable details.
Your calculator export should list: internal pit dimensions and cover class; inlet/outlet positions; pump type and duty point; cable gland details; level setpoints (pump on/off, high alarm); NRV/backflow notes; and an allowance for silt volume. Reference drawing sheets at 931 CAD/BIM Standards and ensure consistency with 934 Duct & trench details.
For submission, include a calculation snapshot in the pack and list the export in the 911 File Index with IDs that match sheet references.
927.5 Limits
Check authority rules and permits (134, 218). Local compliance.
Local discharge rules, contamination thresholds and groundwater dewatering permits vary. Confirm early via the 134 Permit & Inspection Timeline and the site’s 218 Environmental Context. Where gravity discharge is prohibited, the design must show containment, oil–water separator if required, and controlled pumping to an approved point.
927.6 Maintenance
Access, screens, desludging intervals (365, 734). Keeps HVM bollard reliability high.
Provide safe access for basket removal and desludging; size the clear opening and lifting points for routine service. Add a drain tap where practical. Define inspection and cleaning intervals in the 445 design implications context and document the routine in the 734 Preventive Maintenance Plan.
927.7 Validation
Commissioning drain-down tests and records (631–636, 716). Traceable.
At commissioning, perform a controlled fill/drain test (timed volumes) and record pump start/stop levels and high-level alarm latency. Capture evidence to the standard in 631 through 636, with photos/video conforming to 716 Evidence Capture Standards. Keep a copy in the calculations pack and handover set.
927.8 Save/Export
Schedules and typicals with IDs (931, 911). Reviewer-ready for crash rated bollards.
Export a clean schedule (pit sizes, invert levels, pump data, alarm setpoints) and embed drawing callouts that match your 931 CAD/BIM standards. Index the files per the 911 naming rules and include a calculation snapshot page for reviewer traceability.
927.9 Related
Ducting seals, groundwater, surface reinstatement (246, 423, 629). Close interfaces.
Seal duct/pipe entries with rated transit systems and 622 gland details; check seasonal groundwater uplift against 423; and restore surface finishes per 629 reinstatement & interfaces to keep drainage inlets free.
Related
External resources
927 Drainage Sump Sizing — FAQ
How do I pick between gravity drainage and a pumped sump?
What allowance should I make for silt and debris?
Include a silt basket and a dedicated silt pocket. In event-heavy or landscaped areas, reserve 20–30% of effective volume as a silt zone and specify inspection/cleaning intervals in the Preventive Maintenance Plan (734).
Which alarms are essential for automatic bollard pits?
At minimum: pump run, pump fail, and high-level alarm; add an external beacon or SCADA point if flooding could affect automatic bollard operation. Align with site 533 SCADA/BMS signals.
How do I document the sump sizing for authority reviewers?
Export the calculator schedule (dimensions, levels, pump duty, setpoints), include calculation snapshots, and index files per 911. Package with 717 Authority Submittals and the project 721 Method Statement.