Ames City Hall Campus: Stormwater Improvements Tracy Warner, Municipal Engineer for the City of Ames, IA Jake Moore, Stormwater Specialist for the City of Ames, IA Ryan Benjegerdes, Water Resources Engineer with Bolton & Menk, Inc.
Community Flooding History Aug. 2010 (26.72) June 1975 (25.57) July 1993 (25.53) June 1990 (25.4) Aug. 1993 (25.25) June 1996 (25.13) May 2008 (24.70) July 1993 (24.20) Aug. 2015 (23.98) July 1993 (23.92) July 2014 (23.79) Dec. 2015 (22.84) Sept. 2016 (19.86) Aug. 2015 (19.29) Sept. 2016 (18.68) Flood Stage (21.5) Sept. 2016 (17.42) Aug. 2015 (17.21) June 2015 (16.97) Sept. 2016 (15.56)
Traditional Stormwater Vs. New Approach - Traditional : Collect + Move runoff quickly - Out of sight out of mind - New: Iowa Storm Water Management Manual - Retain runoff on site - Treat runoff prior to release - Consider pre-settlement conditions during Design
Leading the Way Social - Using parking lot as an examples of various BMP s which can be incorporated into project. - Example for future development under city post construction ordinance. - Public Education and outreach - Examples for other sites include 24 th street, Ridgewood, Ash Ave, Blackwood Circle, Billy Sunday Rd.and so on.
Leading the Way Technical [City Stormwater Management Ordinance Requirements] - Water Quality Protection 1.25 storm event 90% of storm events are less than this first flush Treat + Retain on site - Channel Protection 1 year 24 hour event: 2.67 Release at pre-development rate (58) Must detain for minimum 24 hour period
Leading the Way Technical [City Stormwater Management Ordinance Requirements] - Overbank Flood Protection 5 year 24 hour event: 3.81 Restrict post-development peak discharge rate - Extreme Flood Protection 10 year 24 hour event: 4.46 100 year 24 hour event: 7.12 Provide safe conveyance of excess runoff
Plan Overview
Project Design Criteria Design Criteria - Comply with City s ordinance - Detention: post-development > pre-settlement - Pre-settlement mimics natural prairie - Capture and treat WQv
Project Design Challenges Design Challenges - Significant peak flow reduction required Pre-Settlement (cfs) Developed w/o SWM (cfs) 1-year 0.11 5.2 5-year 0.8 8.2 10-year 1.4 9.8 100-year 4.6 16.7 - Limited space to implement detention practices - Off-site pass-through flow
Project Design Alternatives Design Alternatives 1. Full or partial exemption from ordinance 2. Off-site detention and on-site WQv treatment 3. Sub-surface detention a. Storage chambers b. Stone voids (subbase)
Project Design Alternatives Design Alternatives 1. Full or partial exemption from ordinance 2. Off-site detention and on-site WQv treatment 3. Sub-surface detention a. Storage chambers b. Stone voids (subbase)
Design Components Permeable Pavers
Design Components Permeable Pavers
Design Components Permeable Pavers - Primary method for runoff to enter subbase - Concrete band between permeable pavers and HMA - Designed to limit cutting of pavers units - Set on bed of crushed stone
Design Components Rock Storage
Design Components Rock Storage
Design Components Rock Storage - Detention storage within stone voids - Infiltration into underlying soils - Receives runoff from permeable pavers - Minimum depth for paver structure - Varying storage depths based on runoff quantity - Subdrain conveys runoff to storm sewer
Design Components Outlet Control Structure
Design Components Outlet Control Structure
Design Components Outlet Control Structure - Restrict outlet to limit release rate - Controls 1-year through 100-year outflow - Minimal maintenance concern due to filtered runoff
Design Components Bioretention Cells
Design Components Bioretention Cells
Design Components Bioretention Cells - Intercept parking and drive aisle runoff - Rain Guardian pretreatment - Overflow provided to storm sewer
Design Components Storm Sewer Connections
Design Components Storm Sewer Connections
Design Components Storm Sewer Connections
Design Components Storm Sewer Connections - Connect to existing storm sewer - Convey upstream storm sewer through site
Design Components Off-site run-on
Design Components Off-site run-on
Design Components Off-site run-on - Trench drain to intercept off-site runoff - Convey runoff through site without diluting BMPs - Separate biocell for off-site runoff - Overflows into storm sewer
Project Design Final Release Rates - Designed to meet pre-settlement release rates - Allow passage of off-site flows - Excess WQv treatment Allowable (cfs) Post-Development (cfs) 1-year 0.11 0.11 5-year 0.8 0.6 10-year 1.4 1.2 100-year 4.6 4.4 WQv 5,550 ft 3 13,750 ft 3
Construction Schedule - April 2017 October 2017 (Break for 4 th of July) - Spring 2018 finish up SQR and Native Seeding - 2 nd Chip of Parking lot in spring
Construction Parking - Coordinating Parking - Outreach to employees - Temporary parking - Fareway - East lot - West Lots - Other city facilities
Construction Safety Fence - Fence along sidewalks - Tried to keep sidewalks open. - Had to be able to get out dumpsters.
Construction Tree Removal - Trees and shrubs in way of construction. - Contractor worked on weekend. - Trees replaced with native species
Construction Pavement + Utility Removal - Removed Parking lot, curb and gutter. - Found junk and old foundations. - Electric lines and lights were taken down.
Construction Storm Sewer - Removed Storm Sewer - Installed New Storm Sewer - Less pipe required because of combination of pavers, curb cuts, trench drains, and rain guardian structures
Construction Grading - Removed soil to allow for Rock Base. - Grade allows for water to drain toward medians with tiles to control discharge. - Rock depth changed based on grade.
Construction / Rock - No. 2 Stone for Flood Storage up to 27 depth - No. 57 Stone for Choker Layer 4 depth - No. 8 Stone below pavers 2 depth
Construction Curb and Gutter + Paver Restraint - Need rock behind curb and gutter to support it. - Paved restraint. - Biocells and medians dug out after paving was completed to design depths.
Construction Biocells - 5 total on site - Dug after paving - Engineered soil mix - Stone at base - Tile placed 9-15 above bottom to allow for infiltration. - Native plants - Wood Mulch
Construction Soil Quality Restoration - Top soil mixed with 2 of compost tilled 8 deep - Applied to all planted and seeded areas (4197 Square Yards) - Medians tipped slightly inward to direct water to center with trees.
Construction Permeable Pavers - Placed with small backhoe and paver attachment. - Curb and Gutter with separation beam must be square. - Rock Chip 2X
Construction Asphalt - Base 4 - Surface 2 - Rock Beneath Pavers - 27 north half - 15 south half
Construction Paint, signs,
Construction Native Vegetation - Native Turf - Buffalo Grass and Blue Gramma - Native Plants (1,900 + School) - Native Trees - Some plants grown, planted and mulched by students
Construction Drainage - Curb Cuts - Rain Guardian - Trench Drains - Pavers - Decorative Rock to help protect scour
Lessons Learned Construction - Have a watering plan for areas planted by students. - Be ready for outreach and inform contractors on site of events - Facebook live events, New Paper, Ch 12, - Have separate contract for SQR and seeding allowing project to be closed out in fall. - Temp seed two times. - Verify depths of utilities - Removal of Lights and Electric resulted in change orders - Material Availability - Decorative stone came from Minnesota - Make sure everyone is clear on plans/design. - Extended length of the south biocell to add storage capacity
SRF Eligible Items SRF Eligible Item Eligible Portion Mobilization 40% Clearing & Grubbing 40% Soil Quality Restoration 100% Topsoil 100% Excavation 66% Engineered Soil for Biocells 94% Subdrains 100% Manholes 67% Bioretention Curb Cuts and Rain Guardians 100% Permeable Pavers 100% Rock 99% Pavement Removal 38% Native Turf & Plants 100% Construction Survey 40% Hydromulch, Filter Socks, Inlet Protection 100%
Final Construction Costs Construction Item Cost Funding City Hall Parking Lot Reconstruction $948,116.35 Change Order #1 $7,055.00 Change Order #2 $2,941.00 Change Order #3 $55,513.59 Engineering Administration $141,000.00 City Hall Parking Lot Reconstruction Funding $500,000.00 Savings from City Hall Roof Project $161,400.00 IDALS Water Quality Grant $100,000.00 Iowa DNR SRF Sponsored Project Funding $347,250.00 15/16 Storm Water Quality Improvement Program $100,000.00 16/17 Storm Water Quality Improvement Program $100,000.00 Total: $1,154,625.94 $1,308,650.00
Tracy Warner, PE City of Ames Municipal Engineer (515) 239-5160 Twarner@city.ames.ia.us Jake Moore City of Ames Stormwater Specialist (515) 239-5287 Jmoore@city.ames.ia.us Ryan Benjegerdes, PE, CFM Bolton & Menk, Inc. Water Resources Engineer (515) 233-6100 Ryanbe@Bolton-menk.com Thank You