STORMWATER MASTER PLAN TASK FORCE November 20, 2006

2007 STORMWATER MASTER PLAN CITIZENS TASK FORCE  Introduction  Task Force Contact Information  Information Binder 1997 Master Plan CD 1997 Master Plan Maps PowerPoint Presentations

2007 STORMWATER MASTER PLAN CITIZENS TASK FORCE  Review of Traveling Town Hall presentation  Questions & Answers from Task Force

2007 STORMWATER MASTER PLAN CITIZENS TASK FORCE  Storm Events of Record Rainfall gage findings Statistical review and analysis Level of storm protection verse construction cost Storm sewer design Storm sewer design frequency

2007 STORMWATER MASTER PLAN CITIZENS TASK FORCE  Questions & Answers from Task Force  Questions & Answers from Audience

Review - Traveling Town Hall 1997 Stormwater Master Plan  Citizens Complaints  Flooding Problem Maps  Project Solutions  Project Prioritization  Proposed Construction Projects

1997 FLOODING PROBLEM MAP

PROJECT PRIORITIZATION CRITERIA Public Health and Safety Street Flooding Depth Population Served Cost per Population Easement / Right-of-Way Needs Permitting / Regulatory Needs Construction Impacts Coordination with Other Projects Environmental Impacts

PROJECT COMPLETED/DESIGNED LIST

 16 Projects Complete $45 million Construction Cost  23 Projects Incomplete $35 million Construction Cost (Construction Cost in 1997 dollars)

MASTER PLAN UPDATE PROJECT TASKS  Collect Flood Information  Flooding Problem Maps  Project Solutions  Project Prioritization  Proposed Construction Projects  Funding Alternatives

MASTER PLAN UPDATE PROJECT TASKS  Collect Flood Information Flooding Questionnaires Building Commission Reported Damage Database City Engineer Database Water & Sewer Utility Database  Flooding Problem Maps  Project Solutions What storm event will we design to? Rainfall statistical frequencies Comparing apples to apples Local gage readings

MASTER PLAN UPDATE PROJECT TASKS  Project Prioritization Add/Remove Categories Evaluate Category Scoring & Criteria Evaluate Category Weighting Factors  Proposed Construction Projects Review Project Capacities (16 Completed Projects) Update Project Limits and Costs (23 Uncompleted Projects) Develop New Projects Coordinate with the Combined Sewer Program

MASTER PLAN UPDATE PROJECT TASKS  Use Project Prioritization  Use Proposed Construction Projects  Final Project Prioritization  Investigate Alternatives in Funding

STORM EVENTS OF RECORD  Rainfall Amounts  Storm Duration  Rainfall Intensity  Statistical Frequency Rainfall gage locations Rainfall gage recording intervals  What storm event will we design to?

STORM EVENTS OF RECORD Theoretically, Evansville has a 4% chance every year to receive one of the following storms: 2.4 inches in 1 hour 3.0 inches in 2 hours 3.3 inches in 3 hours 4.0 inches in 6 hours How many “4% chance” storms has the City received? It depends which rain gage you look at.

STORM EVENTS OF RECORD

 Using a 24-hour rain gage at the Evansville Airport over the last 110 years, we have received the following storms: 0 – 1% Storm(1) 1 – 2% Storm(2) 3 – 4% Storms(4) 5 – 10% Storms(10) 13 – 20% Storms(20)

STORM EVENTS OF RECORD

 Using an hourly rain gage at the EWWTP over the last 10 years, we have received the following storms: 1 – 1% Storm(0.1) 3 – 2% Storms(0.2) 4 – 4% Storms(0.4) 7 – 10% Storms(1.0) 9 – 20% Storms(2.0)

STORM EVENTS OF RECORD

 Using an hourly rain gage in Henderson over the last 5 years, we have received the following storms: 1 – 2% Storms(0.1) 2 – 4% Storms(0.2) 3 – 10% Storms(0.5) 8 – 20% Storms(1.0)

STORM EVENTS OF RECORD Conclusion: Theoretical storm intervals are conservative compared to the Airport daily gage information. Theoretical storm intervals become more accurate compared to The Airport hourly gage information. The City has received 4-10 times as many higher frequency storms at other gage locations compared to the theoretical intervals over the last 10 years.

Three Hour Rainfall Sept. 12, :30 pm to 4:30 pm 3 to 4 inches of rain fell over the Southeast side of Evansville in this 3 hour period

LEVEL OF PROTECTION COSTS  The Potential Maximum Precipitation in Evansville for a 24-hour period is 35 inches!!!  How costly would it be to provide such a drainage network to provide relief?  Every level of protection has an associated increase in construction cost. GENERAL cost increases: “4% Chance” Storm$10,000,000 “2% Chance” Storm$13,000,000 “1% Chance” Storm$16,500,000

ENGINEERING A LEVEL OF PROTECTION  Engineer the design to the requested level of protection.  Gravity solutions will include a factor of safety. When pressure is added to the drainage system, there is an additional level of protection.  How much added protection is project dependant.

MASTER PLAN UPDATE PROJECT TASKS ■ Collect Flood Information Flooding Questionnaires Building Commission Reported Damage Database City Engineer Database Water & Sewer Utility Database ■ Flooding Problem Maps  Project Solutions What storm event will we design to?

STORMWATER MASTER PLAN TASK FORCE November 20, 2006