Related to Stormwater Drainage Systems

Case Study: Phoenix Airport Storm Drain Interference (2020)

Project Overview

• Name: Sky Harbor Taxiway Extension
• Location: Phoenix, Arizona
• Year: 2020
• Project Size: $220 million
• Scope: Taxiway extension including major stormwater system rerouting
• Lead Agencies/Contractors: Phoenix Aviation Dept. /

Category of the Issue, Problem, or Challenge

• Stormwater Infrastructure
• Utility Coordination

Summary of the Issue, Problem, or Challenge
During excavation for the new stormwater main, crews struck and ruptured an active drainage trunk line that had not been clearly shown in as-built documents, resulting in sediment-laden water flooding the trench and adjacent apron.

Root Cause Analysis

Impacts Due to the Issue, Problem, or Challenge

• Flooding of adjacent airfield area, delaying paving operations
• Emergency dewatering and trench support mobilization
• Insurance claim and internal review of coordination procedures

Corrective Actions Taken

1. Mandatory subsurface utility engineering (SUE) for all storm drain corridors
2. Revised utility approval protocols with GPR verification
3. Updated stormwater decommissioning documentation process

Lessons Learned

• Storm drainage systems may differ significantly from records
• Major trenching should always be preceded by subsurface verification
• Utility misidentification near storm drains can cause flooding and delays

Case Study: Atlanta Detention Tank Construction Collapse (2018)

Project Overview

• Name: BeltLine Southeast Segment
• Location: Atlanta, Georgia
• Year: 2018
• Project Size: $150 million
• Scope: Urban trail and greenway project with underground stormwater detention infrastructure
• Lead Agencies/Contractors: Atlanta BeltLine Inc. /

Category of the Issue, Problem, or Challenge

• Deep Excavation
• Stormwater Detention

Summary of the Issue, Problem, or Challenge
A precast underground stormwater detention vault collapsed during installation due to lateral pressure from adjacent saturated soils after a series of heavy rains.

Root Cause Analysis

Impacts Due to the Issue, Problem, or Challenge

• Collapse damaged installed precast sections and nearby utilities
• Major delay and cost impact to trail opening
• Investigation by city risk management division

Corrective Actions Taken

1. Updated shoring and backfill protocols for detention structures
2. Required groundwater monitoring for all deep vault sites
3. Training on phased installation under wet conditions

Lessons Learned

• Precast detention systems require dry, well-compacted bases
• Wet-weather work demands special precautions for excavation and backfill
• Risk increases when construction speed overtakes drainage site readiness

Case Study: Dallas Subdivision Detention Pond Breach (2022)

Project Overview

• Name: South Dallas Flood Control Improvements
• Location: Dallas, Texas
• Year: 2022
• Project Size: $95 million
• Scope: Regional stormwater detention and neighborhood flood mitigation
• Lead Agencies/Contractors: Dallas Water Utilities /

Category of the Issue, Problem, or Challenge

• Stormwater Detention
• Earthwork

Summary of the Issue, Problem, or Challenge
A newly constructed earthen detention pond experienced a breach during an unexpected rain event. The embankment had not yet been fully compacted and stabilized, and water overtopped the inlet control structure, eroding a slope and causing partial failure.

Root Cause Analysis

Impacts Due to the Issue, Problem, or Challenge

• Adjacent properties flooded during breach
• Rework of pond liner, slope stabilization, and sediment removal
• Additional oversight from FEMA due to partial federal funding

Corrective Actions Taken

1. Mandatory pre-storm inspections and pond monitoring
2. Emergency action plans required for detention features in progress
3. Use of real-time erosion control sensors on critical embankments

Lessons Learned

• Storm events can severely impact incomplete detention systems
• Temporary drainage features must be sized and maintained for active weather
• Final stabilization cannot be deferred near major storm seasons

Case Study: Spokane Culvert Collapse During Fill (2016)

Project Overview

• Name: Highway 195 Widening Project
• Location: Spokane, Washington
• Year: 2016
• Project Size: $73 million
• Scope: Road widening and new storm culvert installations
• Lead Agencies/Contractors: Washington State DOT

Category of the Issue, Problem, or Challenge

• Culvert Installation
• Embankment Fill

Summary of the Issue, Problem, or Challenge
A 48-inch reinforced concrete pipe culvert collapsed during fill operations after being improperly backfilled without adequate lift compaction and with heavy equipment operating directly overhead.

Root Cause Analysis

Impacts Due to the Issue, Problem, or Challenge

• Pipe replacement and realignment caused 4-week delay
• Cost increase due to excavation redo and temporary detours
• DOT updated trench safety and pipe install procedures

Corrective Actions Taken

1. Pre-installation training on pipe zone backfill
2. Use of lightweight fill materials in early lifts
3. Design documents updated with constructability notes for culverts

Lessons Learned

• Culvert protection during fill requires strict adherence to compaction plans
• Heavy loading over buried storm infrastructure must be carefully sequenced
• Communication gaps between designers and crews can lead to structural loss

Case Study: Charlotte Sediment Basin Overflow into Creek (2019)

Project Overview

• Name: I-485 Outer Loop Completion
• Location: Charlotte, North Carolina
• Year: 2019
• Project Size: $290 million
• Scope: New highway loop segment with roadside drainage and environmental controls
• Lead Agencies/Contractors: North Carolina DOT

Category of the Issue, Problem, or Challenge

• Erosion Control
• Stormwater Sediment Management

Summary of the Issue, Problem, or Challenge
A temporary sediment basin failed to capture runoff during a series of construction-phase storms, discharging silt-laden water into a protected creek and violating state environmental permits.

Root Cause Analysis

Impacts Due to the Issue, Problem, or Challenge

• Fines from the NC Department of Environmental Quality
• Temporary work stoppage for environmental compliance review
• Increased monitoring frequency for all sediment basins on project

Corrective Actions Taken

1. Redesign of sediment basins to larger capacity
2. Weekly inspections with mandatory sediment removal thresholds
3. Training for erosion control subcontractors on storm forecasting protocols

Lessons Learned

• Sediment basins must be maintained below critical thresholds
• Secondary erosion control systems should be installed during storm seasons
• Runoff volume projections must include margin for construction disturbance

Case Study: Seattle Outfall Pipe Displacement (2017)

Project Overview

• Name: Alaskan Way Viaduct Replacement
• Location: Seattle, Washington
• Year: 2017
• Project Size: $3.3 billion (overall project)
• Scope: Waterfront tunnel construction with multiple stormwater outfall relocations
• Lead Agencies/Contractors: Washington State DOT /

Category of the Issue, Problem, or Challenge

• Stormwater Outfall
• Utility Relocation

Summary of the Issue, Problem, or Challenge
During installation of a large stormwater outfall pipe to the Puget Sound, crews discovered that the pipe alignment shifted due to unstable trench walls and water infiltration during dewatering. The misalignment required re-excavation and realignment.

Root Cause Analysis

Impacts Due to the Issue, Problem, or Challenge

• Two-week delay in outfall completion
• Increased costs for additional excavation and pipe replacement
• Risk mitigation reviews implemented for other utility relocations

Corrective Actions Taken

1. Enhanced trench support systems including sheet piling
2. Upgraded dewatering pumps and monitoring
3. Weather-sensitive scheduling policies introduced

Lessons Learned

• Outfall trench stability is critical and requires robust shoring and water management
• Dewatering design must exceed minimum expected infiltration during wet seasons
• Scheduling should avoid high-risk weather periods for critical underground utilities

Case Study: Houston Grading Conflict with Stormwater Swale (2018)

Project Overview

• Name: Grand Parkway Segment D
• Location: Houston, Texas
• Year: 2018
• Project Size: $750 million
• Scope: Highway construction with extensive roadside stormwater swales
• Lead Agencies/Contractors: TxDOT /

Category of the Issue, Problem, or Challenge

• Grading
• Stormwater Conveyance

Summary of the Issue, Problem, or Challenge
During rough grading operations, the planned elevation for a stormwater swale was raised inadvertently due to contractor error, causing water to pond upstream and flooding a neighboring construction zone.

Root Cause Analysis

Impacts Due to the Issue, Problem, or Challenge

• Flood damage to adjacent stockpile areas and temporary utilities
• Project delay of 3 weeks to regrade and reconstruct swale
• Increased contractor claims and disputes over responsibility

Corrective Actions Taken

1. Implementation of grade verification checkpoints at key milestones
2. Cross-disciplinary communication protocols for grading changes
3. Use of GPS-controlled equipment for swale grading

Lessons Learned

• Small grading errors can disrupt stormwater conveyance and cause flooding
• Continuous verification during earthwork is essential for critical drainage features
• Clear communication channels reduce risk of undocumented changes

Case Study: Denver Infiltration Basin Underperformance (2019)

Project Overview

• Name: E-470 Tollway Extension
• Location: Denver, Colorado
• Year: 2019
• Project Size: $400 million
• Scope: Tollway extension with multiple infiltration basins to manage stormwater
• Lead Agencies/Contractors: E-470 Public Highway Authority

Category of the Issue, Problem, or Challenge

• Stormwater Infiltration
• Environmental Compliance

Summary of the Issue, Problem, or Challenge
Post-construction testing of infiltration basins revealed poor infiltration rates caused by improper soil amendment and compaction during basin construction, resulting in surface ponding and permit compliance risks.

Root Cause Analysis

Impacts Due to the Issue, Problem, or Challenge

• Required retrofitting of infiltration basins with soil loosening and amendment
• Delay in project closeout and environmental certification
• Additional monitoring imposed by local environmental agency

Corrective Actions Taken

1. Revised soil preparation protocols with mandatory testing and verification
2. Training for earthwork crews on infiltration system requirements
3. Incorporation of independent QA testing before basin acceptance

Lessons Learned

• Infiltration basin effectiveness depends heavily on soil treatment and compaction control
• Design intent must be strictly enforced during earthwork for stormwater systems
• QA processes should include functional performance tests, not just visual inspections