Completion Date
March 2023
Options Evaluated
7 Strategies
Study Period: Multi-year comprehensive analysis completed March 6, 2023
Study Location
Primary Area: Butler County, Missouri - Black River Watershed
Extent: From Clearwater Dam to Corning, Arkansas (approximately 200 miles)
Study Purpose
This comprehensive hydrologic analysis was conducted to evaluate flooding issues and identify potential mitigation strategies along the Black River in Southeast Missouri. The study addresses concerns from local communities about increased flooding frequency and duration.
Analysis Components
- Clearwater Dam operational scenario analysis
- Geomorphic mapping and channel analysis
- Precipitation and streamflow trend analysis
- Groundwater-surface water interaction modeling (GSSHA)
- Surface water hydraulic analysis (HEC-RAS)
- Historical channel stability assessment (1948-2019)
Primary Finding: Recent flooding is primarily driven by increased precipitation patterns, not channel changes or dam operations.
Precipitation Trends
- Annual Totals: Statistically significant increases in total precipitation
- Storm Intensity: Higher intensity rainfall events occurring more frequently
- Event Frequency: More frequent high-intensity precipitation events
- Climate Pattern: Long-term trend indicating continued increases
Streamflow Changes
- Baseflow: Significant increases in baseline river flows
- Runoff Component: Higher volume and faster response to precipitation
- Peak Flows: Increased magnitude of flood events
- Duration: Extended periods of elevated water levels
Groundwater Impact
The study revealed high connectivity between groundwater and surface water in the Black River watershed. This connection prolongs flooding conditions even after surface water levels begin to recede, creating extended periods of agricultural impacts.
Channel Stability
Historical Analysis: No major bed elevation changes detected from 1948-2019, confirming that flooding increases are precipitation-driven rather than caused by channel degradation or aggradation.
⚠ LIMITED BENEFIT
Description
Remove short transverse levees at the Coon Island Conservation Area to allow floodwaters to access additional storage area.
Impact Analysis
- Water Surface Reduction: Very localized reduction up to 1 foot
- Flow Range: Benefits limited to 4,000-5,000 cfs flow range
- Flood Duration: Minimal impact on overall flood duration
- Geographic Extent: Benefits confined to immediate vicinity
Assessment
Recommendation: Local drainage improvements (Option 2) would provide more predictable and widespread benefits than this targeted levee removal. Consider only as part of comprehensive strategy.
✗ NOT RECOMMENDED
Description
Extensive, system-wide channel dredging to remove accumulated sediments and increase channel capacity throughout the study area.
Concerns & Risks
Significant Risks Identified:
- Downstream Impacts: May increase water levels downstream during high flows
- Head Cutting: Risk of upstream-migrating channel degradation
- Bank Failures: Could trigger widespread bank instability
- Levee Threats: May undermine nearby levee systems
- Limited Duration Impact: Minimal effect on flood duration
- High Costs: Extremely expensive implementation and maintenance
- Temporary Benefits: Channel will naturally fill in over time
Technical Analysis
Modeling results indicate that comprehensive dredging could create channel instability that propagates both upstream and downstream. The risks of infrastructure damage and environmental harm outweigh potential benefits.
✗ NOT RECOMMENDED
Description
Create artificial cutoffs through meander bends to shorten river length and increase gradient, theoretically improving conveyance capacity.
Significant Risks
Multiple Critical Concerns:
- Continued Degradation: Initiates ongoing channel degradation and head cutting
- Bank Failures: Triggers widespread bank failures threatening infrastructure
- Levee Systems: Places existing levee systems at severe risk
- High Construction Costs: Extremely expensive to implement
- Perpetual Maintenance: Creates ongoing maintenance requirements
- Habitat Disruption: Destroys valuable aquatic and riparian habitat
- Floodplain Disconnection: Eliminates beneficial floodplain functions
Limited Feasibility
Spatial Constraints: Only potentially considered feasible in limited areas with large floodplain width on both sides of the river. Even in these locations, risks substantially outweigh benefits.
Historical Context
Historical channelization projects in similar settings have demonstrated long-term negative consequences including perpetual instability, high maintenance costs, and environmental degradation. Modern engineering practice has moved away from this approach.
✗ NOT EFFECTIVE
Description
Evaluate alternative operating scenarios for Clearwater Dam to determine if modified release patterns could reduce downstream flooding impacts.
Analysis Results
Ineffective and Potentially Harmful:
- Increased Spillage: Attempts to limit releases result in increased uncontrolled spillage
- Dam Safety Risk: Creates potential risk to dam safety and structural integrity
- Higher Peak Releases: Results in higher peak releases when spillway is activated
- More Critical Days: Increases number of days above critical elevation thresholds
- No Downstream Benefit: Provides no measurable benefit to downstream flood conditions
- Worse Outcomes: Generally produces worse flooding outcomes than current operations
Technical Findings
Multiple operational scenarios were modeled and tested. All alternatives to current operations either provided no benefit or resulted in worse conditions downstream. Current dam operations are optimized for both dam safety and downstream flood reduction.
Conclusion: Clearwater Dam is not a contributing factor to increased flooding. Changes in precipitation patterns, not dam operations, are driving observed flooding increases.
Recommended Combined Approach: The study recommends implementing multiple strategies in a coordinated, phased manner to maximize effectiveness while managing costs and community impacts.
Immediate Actions (Year 1)
- Standard Channel Maintenance: Initiate debris removal and channel clearing from Hargrove Pivot Bridge to state line
- Safety Improvements: Address immediate safety concerns from accumulated debris
- Flow Monitoring: Establish enhanced monitoring at key locations
- Community Engagement: Begin stakeholder coordination for longer-term solutions
Short-Term Implementation (Years 1-3)
- Two-Stage Ditches: Design and implement pilot two-stage ditch projects
- Local Drainage: Upgrade priority local drainage systems
- Tile Drainage: Install subsurface drainage in high-priority agricultural areas
- Performance Assessment: Monitor and evaluate effectiveness of initial implementations
- Adaptive Management: Refine approaches based on monitoring results
Long-Term Strategies (Years 3-10)
- Strategic Levee Setbacks: Pursue opportunities for levee setbacks with willing landowners
- Conservation Easements: Develop voluntary floodplain easement programs
- System-Wide Drainage: Expand successful two-stage ditch designs watershed-wide
- Comprehensive Monitoring: Maintain long-term monitoring network
- Adaptive Framework: Adjust strategies based on changing climate patterns
Funding Opportunities
Potential Funding Sources:
- USACE Continuing Authorities Program (CAP)
- NRCS Emergency Watershed Protection Program
- FEMA Hazard Mitigation Assistance
- State emergency management grants
- Agricultural conservation programs
- Local cost-share partnerships
Success Metrics
Implementation success will be measured through:
- Reduction in water surface elevations during flood events
- Decreased duration of flooding conditions
- Improved agricultural productivity in affected areas
- Reduced groundwater flooding impacts
- Enhanced community resilience to flooding
- Cost-benefit analysis of implemented measures
- RECOMMENDED ========================================================================= -->
✓ RECOMMENDED
Description
Implement standard channel maintenance from Hargrove Pivot Bridge to the state line, with flow control structure at Swift Ditch. This approach mirrors successful USACE clearing projects from the 1990s.
Benefits
- Water Level Reduction: Approximately 0.5 feet reduction in water surface elevations
- Natural Scouring: Allows river to naturally maintain capacity through self-scouring
- Safety Improvement: Addresses concerns from accumulated debris
- Sustainability: Maintainable with regular, routine clearing operations
- Cost-Effective: Lower implementation and maintenance costs
Implementation Approach
Standard maintenance equivalent to 1990s USACE clearing project methodology. Focus on removing accumulated debris and restoring channel capacity without extensive excavation.
Key Advantage: This option provides immediate, measurable benefits while allowing natural river processes to continue maintaining channel capacity.
✓ RECOMMENDED
Description
Improve local drainage systems through enhanced ditch designs incorporating two-stage channel features, potentially supplemented with subsurface tile drainage systems where appropriate.
Benefits
- Groundwater Management: Significant impact on reducing groundwater flooding issues
- Targeted Approach: More focused solution for agricultural drainage needs
- Groundwater Reduction: Reduces groundwater surface elevations by approximately 0.5 meters
- Best Practice: Proven design for areas with perennial flow conditions
- Maintenance Benefits: Reduces frequency of required ditch cleaning
- Environmental Benefits: Provides habitat features while improving drainage
Best Application Areas
Most effective in locations where ditches require frequent maintenance due to sediment deposition. Particularly valuable in areas with high groundwater tables and where agricultural productivity is limited by prolonged saturation.
Two-Stage Design: Features a low-flow channel with adjacent benches that provide additional capacity during high flows while reducing erosion and providing ecological benefits.
✓ RECOMMENDED
Description
Relocate existing levees away from the river channel to provide additional floodplain area, reducing water surface elevations and pressure on flood protection infrastructure.
Benefits
- Maximum WSE Reduction: Greatest water surface elevation reduction (2-6 feet)
- Levee Protection: Reduces pressure and failure risk on existing levee systems
- Duration Reduction: Significantly reduces flood duration from weeks to days
- Natural Processes: Provides space for natural river meandering and sediment transport
- Ecosystem Services: Creates valuable riparian habitat and floodplain functions
- Long-term Solution: Most sustainable approach for changing climate conditions
Implementation Considerations
Land Acquisition: This option generally requires land acquisition and is often unpopular with landowners due to loss of agricultural acreage. Success requires willing sellers and community support.
Strategic Application
Most effective when implemented strategically in key locations where setbacks provide maximum benefit. Opportunities may arise through voluntary enrollment programs, conservation easements, or as part of larger watershed management initiatives.