Construction Inspection Checklist for Extended Detention Basins
Introduction
Proper construction of permanent stormwater best management practices (BMPs) is essential to ensure BMPs achieve their treatment objectives; namely reducing the amount of stormwater runoff and pollution discharged to local lakes, rivers and streams.
This construction inspection checklist is intended to reduce construction errors for extended detention basins (one type of BMP). These errors can result in inadequate BMP performance and/or expensive maintenance and rehabilitation costs for the BMP owner. This checklist should be filled out by an inspector, construction supervisor and/or design engineer throughout the duration of BMP construction to assure that the BMP is installed correctly.
The items herein assume that designs follow those recommended in Volume 3 of the Urban Drainage and Flood Control District Design Criteria Manual. In some locations, design criteria may be different and certain items may not apply.
Pre-Construction
1.1 - Pre-Construction Meeting
A pre-construction meeting should be held between design engineers, project managers, contractor foreman and other relevant personnel to discuss important aspects of BMP installation, including (but not limited to) verifying the items outlined in this document.
Forebay/Energy Dissipation
2.1 – Forebay
Verify the forebay is gently sloped towards the outlet pipe or notched weir.
2.2 – Energy Dissipation
Verify that energy dissipation materials (rip-rap or other) meet design specifications and are installed according to design.
Trickle Channel
3.1 – Shape and Sizing
Verify that the trickle channel shape, width and depth are according to design.
3.2 – Slope
Verify that trickle channel is sloped (continuously) towards the outlet structure.
Micropool
4.1 – Size and Depth
Verify the micropool’s length, width and depth (generally 1-3 feet) are installed according to design.
Outlet Structure
5.1 – Trash Rack
Verify dimensions and type of trash rack (well screen or grate) are consistent with design specifications. Visually verify that trash rack openings are smaller than openings on the orifice plate.
5.2 – Trash Rack (with micropool)
Verify that trash rack extends all the way to the bottom of the micropool. Note: This only applies if the design includes a micropool.
5.3 – Water Quality Capture Volume (WQCV) Orifice Plate
Verify the number and size of orifices are consistent with design specifications. Verify the orifice plate is bolted to the structure with gasket material placed between the structure and the plate. Verify the lowest orifice is at an elevation lower than the trickle channel invert. Note: If design includes a micropool ensure that the bottom most orifice should be located at the design water surface elevation of the micropool.
5.4 – Well Screen/Orifice Plate Cap
Verify that a metal cap/plate is installed on top of the opening between the well screen and WQCV orifice plate.
5.5 – Safety Grate
If a safety grate is included in the design, verify dimensions of safety grate are consistent with design specifications.
5.6 – Signage
Verify “outlet structure modification” warning sign is per design specifications. Note: Not all municipalities require this type of signage.
Emergency Overflow/Spillway
6.1 – Weir Length and Depth
Verify length and depth of emergency overflow weir is per design specifications.
6.2 – Elevation
Verify emergency spillway elevation is lower than the rest of the basin embankments/walls and higher than the outlet structure overflow.
6.3 – Energy Dissipation
Verify rip-rap or other energy dissipation methods are installed downstream of the emergency spillway, per design specifications.
Final Landscaping
7.1 – Construction Sediment Removal
If the EDB provided construction sediment control, verify removal of all construction sediment from the basin and the upstream catchment is stable prior to landscaping.
7.2 – Vegetation
Verify seeding application rates were per landscape design specifications.
7.3 – Irrigation
Verify irrigation placement (permanent or temporary) to ensure proper establishment of vegetation.
Close Out
8.1 – Upstream Catchment Stabilization
Prior to removing temporary sediment control BMPs, verify construction in the upstream catchment is complete and landscaped areas are properly vegetated or otherwise stabilized.
Construction Inspection Checklist for Extended Detention Basins
Project: ______Site: ______
Inspector: ______Company: ______
No. / Item/Activity / Pass / Fail / N/A / Date / NotesPre-Construction
1.1 / Pre-construction meeting held to discuss BMP installation, inspection and checklist
Forebay/Energy Dissipation
2.1 / Forebay is gently sloped towards outlet pipe/notched weir
2.2 / Energy dissipation materials (e.g. rip-rap) are installed according to design
Trickle Channel
3.1 / Shape, width and depth meet design specifications
3.2 / Slope is gentle and continuous towards the outlet structure
Micropool
4.1 / Length, width and depth dimensions meet design specifications
Outlet Structure
5.1 / Trash rack dimensions and type meet design specifications
5.2 / Trash rack extends to the bottom of the micropool (if a micropool is present)
5.3 / Number and size of orifices meet design specifications
5.4 / Metal cap/plate is installed on top of the opening between the well screen and orifice plate
5.5 / Safety grate size and type meet design specifications
5.6 / Outlet structure modification sign is installed per design specifications
Emergency Overflow/Spillway
6.1 / Overflow weir length and depth meet design specifications
6.2 / Overflow weir is lower that top of basin walls/embankments and higher than outlet structure overflow
6.3 / Rip-rap or other energy dissipation is installed downstream of the spillway, per design specifications
Final Landscaping
7.1 / Verify removal of all construction sediment from basin prior to landscaping.
7.2 / Verify type and application rate of seeding meets landscape design specifications
7.3 / Verify irrigation installation (temporary or permanent)
Close Out
8.1 / Verify upstream catchment is stable prior to diverting runoff into the basin