DISCLAIMER: This analysis is prepared by Sreekanth Pannala, LID 19 Board Member, for informational and educational purposes only. This document does not represent the official position of Fort Bend County Levee Improvement District No. 19 or any affiliated organizations. The flood simulation data presented herein is based on modeling approximations and should not be used for emergency planning, insurance claims, or legal purposes. For official flood information, contact the Fort Bend County Drainage District or FEMA.

FLOOD ANALYSIS CASE STUDY

Fort Bend LID 19

Hurricane Harvey Flood Response

Analysis of drainage infrastructure performance during the historic 35-inch rainfall event of August 2017

777
Total Acres
35"
Total Rainfall
44 hrs
Outfall Blocked
~500
Structures Flooded
Prepared by Sreekanth Pannala | LID 19 Board Member
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Fort Bend LID 19 Overview

Riverstone Community Flood Protection System

LID19 Elevation Map
Ground Elevation
59 - 67 ft NAVD88

District Characteristics

777
Total Acres
2.5 mi
Herrin Levee
3
Detention Ponds
241
Snake Slough Acres

Drainage Infrastructure

  • Gravity Outfall Structure

    Primary drainage to Brazos River via Snake Slough

  • Pump Station

    Backup drainage when gravity outfall is blocked

  • Herrin Levee

    Protection from Brazos River flooding (67+ ft crown)

  • Detention Ponds J, J-Small, O

    Combined 75 acres of stormwater storage

Hurricane Harvey Impact

August 25-30, 2017 | Category 4 Landfall

35"
Total Rainfall in LID19
Over 5 days
59 ft
Peak Brazos River Stage
At Richmond Gauge
44 hrs
Gravity Outfall Blocked
River > 45 ft threshold

Compound Flooding Challenge

Intense Rainfall
35" in 5 days
River Flooding
Brazos at 59 ft
Blocked Drainage
No gravity outfall

Event Timeline

120-Hour Storm Progression

Hour 0
Aug 25, 6PM
Harvey Landfall
Rain begins over LID19
Hour 46
Aug 27, 4PM
Outfall Blocked
Brazos exceeds 45 ft
Closed
Hour 72
Aug 28, 6PM
Peak Stress
34" cumulative rain
Max flooding
Hour 90
Aug 29, 12PM
Outfall Restored
Brazos recedes
Open
Hour 120
Aug 30, 6PM
Recovery
Normal levels
Event ends
Pump Station Operation 44 hours continuous
Standby ACTIVE (Hours 46-90) Standby

Geographic Flood Analysis

Elevation-based water depth modeling with LiDAR data

Hour 60: Near Peak Conditions

Flood Map Hour 60
Gravity Outfall: BLOCKED Pump Station: ACTIVE

Hour 96: Recovery Phase

Flood Map Hour 96
Gravity Outfall: OPEN Water Draining: NORMAL

Map Legend

Ground Elevation (59-67 ft)
Flood Depth Contours
LID19 Boundary
Herrin Levee

Flood Progression

120-hour animated simulation showing water level changes

Flood Animation
Start
Hour 0
Aug 25
Outfall Blocked
Hour 46
Aug 27
Peak Stress
Hour 72
Aug 28
Recovery
Hour 120
Aug 30

Interactive Simulation

120-hour flood progression with controls

Simulation Control

Current Conditions

0.0"
Rainfall
0.0 ft
Flood Depth
35.0 ft
Brazos Stage
0
Structures at Risk

Infrastructure Status

Gravity Outfall: OPEN
Pump Station: STANDBY
August 25, 2017 6:00 PM Harvey Landfall
LID 19 Boundary Low Elevation (59-62 ft) - ~500 structures Mid Elevation (62-65 ft) High Elevation (65+ ft) Outfall Pump Pond J Pond O Herrin Levee Brazos River ~0.5 mi
Water Level:
0 ft

Flood Impact

Actual flooding in lower elevation areas of LID19

Flood Impact

Structures Flooded ~500
Max Flood Depth (low areas) 2-4 ft
Peak Hour 72
Affected Elevation Range 59-62 ft

Detention Pond Performance

Pond J (35 acres) 36% capacity
Pond J-Small (15 acres) 48% capacity
Pond O (25 acres) 42% capacity

Infrastructure Operations

Gravity Outfall
Primary drainage structure
Blocked: Hour 46 (Brazos > 45 ft)
Restored: Hour 90 (Brazos < 45 ft)
Total Blocked: 44 hours
Pump Station
Backup drainage system
Activated: When outfall blocked
Total Runtime: 44 hours
Status: Performed flawlessly

Pump Station Upgrade

Infrastructure improvements since Harvey

Before Upgrade (2017)

Pump Capacity 60,000 GPM
Spare Capacity +20,000 GPM
Max Flood Depth 2.8 ft
Structures at Risk ~500

After Upgrade (Current)

Pump Capacity 500,000 GPM
Projected Flood Depth 0.4 ft
Structures at Risk ~40
8.3x
Capacity Increase
86%
Flood Depth Reduction
~460
Structures Protected
Modeling Uncertainty: The projected 0.4 ft flood depth may not impact most structures as many homes are built at slight elevation above their plats. This simulation is based on simplified hydraulic assumptions. Actual flood depths during any future event will vary based on storm characteristics, antecedent conditions, and infrastructure performance. Events with the exact characteristics of Hurricane Harvey (35" over 5 days with simultaneous Brazos River flooding) are extremely rare - Harvey was a 1-in-500+ year event for this region.

Simulation based on identical Harvey conditions (35" rainfall, 44-hour outfall blockage)

Flood Animation Comparison

Side-by-side 120-hour simulation: Before vs After pump upgrade

Pump Upgrade Animation Comparison

Before Upgrade

60,000 GPM (+20K spare)
  • Peak flood depth: 2.8 ft
  • Structures at risk: ~500
  • Full drainage: ~30 hours after outfall restored

After Upgrade

500,000 GPM
  • Peak flood depth: 0.4 ft
  • Structures at risk: ~40
  • Full drainage: ~15 hours after outfall restored
Animation shows identical Harvey conditions (35" rainfall, 44-hour outfall blockage)

Analysis Dashboard

Comprehensive simulation outputs

LID19 Summary Dashboard
View All Generated Plots

Key Takeaways

Lessons from Hurricane Harvey

Pump Upgrade Impact

The 8.3x pump capacity upgrade (60K to 500K GPM) means that in a repeat Harvey scenario, virtually no homes would flood - a dramatic improvement from ~500 flooded structures in 2017.

  • Flood depth reduced from 2.8 ft to 0.4 ft (86% reduction)
  • 0.4 ft likely absorbed by home pad elevation above grade
  • Faster drainage: ~15 hours vs ~30 hours after outfall restored

Compound Flooding Risk

The combination of intense rainfall and elevated river levels creates compound flooding scenarios that require coordinated infrastructure response.

  • 44 hours without gravity drainage is a significant stress test
  • Pump station maintenance is critical for emergency readiness
  • Climate change may increase frequency of such events

Modeling Value

Physics-based flood simulation provides insights into system behavior that support infrastructure planning and emergency preparedness.

  • Identifies critical thresholds (e.g., 45 ft Brazos stage)
  • Quantifies infrastructure requirements for future events
  • Supports communication with residents and stakeholders

Community Awareness

Understanding flood risk and infrastructure capabilities helps residents make informed decisions during extreme weather events.

  • Know your elevation relative to flood protection systems
  • Monitor Brazos River levels during rain events
  • Support LID infrastructure maintenance investments

Thank You

For questions about LID19 flood protection infrastructure, please contact the Fort Bend County Levee Improvement District No. 19.

Resources

Fort Bend County Drainage District
fbcdd.org
FEMA Flood Maps
msc.fema.gov
Brazos River Levels
waterdata.usgs.gov
NWS Houston
weather.gov/hgx

Prepared by Sreekanth Pannala | LID 19 Board Member

For informational purposes only. Does not represent the official position of LID 19.