Stormwater: Operation & Maintenance
STORMWATER: OPERATION & MAINTENANCE
DETENTION BASIN GUIDE
City of Springfield • Department of Environmental Services 290 E. Central St. Springfield, MO 65802 • 417.864.1996 springfieldmo.gov/stormwatermaintenance TABLE OF CONTENTS
What is a Detention Basin? 3 Detention Basin Basics 3 Basin Responsibility 3 CONTACTS Types of Basins 4 City of Springfield Department of Environmental Services Anatomy of a Basin 4 Stormwater | Water Quality Division 290 E. Central St. How to Care for a Detention Basin 5 Springfield, MO 65802 REPORT POLLUTION (417) 864.1011 Developing a Maintenance Plan 5
Easy Ways to get Started 6 SOCIAL MEDIA Vegetation Management 6 How to Improve an Existing Basin 7
Retrofits and Enhancements 7 QUICK LINKS Glossary of Words & Terms 8 springfieldmo.gov/stormwater Self Inspection List 9-12 springfieldmo.gov/environment
INTRODUCTION
Purpose of this Guide This is intended to be utilized as a practical aid to inform, educate and assist in the ongoing maintenance and inspections recommended for responsible operation of a detention basin. This guide has been created to detail the different forms of basins, their anatomy, address responsibility inquiries, provide operational and preventative maintenance tasks and a self-inspection checklist. City Code Chapter 96 Article 1 Division 2 Section 96-14 (a) All stormwater control measures and stormwater drainage systems shall be operated and maintained by the responsible party so as to prevent any nuisance conditions and to ensure full functionality, as designed, and in conformity with any approved stormwater plans and any approved operation and maintenance plan and agreement.
(b) Operation and maintenance of all stormwater control measures constructed subsequent to the adoption of this article shall be ensured through the creation of an operation and maintenance plan and agreement which shall meet all applicable requirements set forth in the flood control and water quality protection manual and shall be approved prior to construction of the stormwater control measures. (G.O. No. 6445, § 1, 4-9-2018)
This guide was prepared by the Stormwater Division of the City of Springfield’s Environmental Services Department. All photographs and graphics created by departmental staff. Created in August of 2019. Get the basin basics here. WHAT IS A DETENTION BASIN?
Basin 101 A detention basin is a specifically designed stormwater control measure (SCM) that is intended to reduce the impacts of pollutants in stormwater runoff, while simultaneously holding stormwater during heavy rain periods and increased snow melt in order to slow the rate of stormwater and minimize the potential for flooding and erosion problems downstream. Why are they built? Basins exist naturally, but detention basins are specifically engineered depressions that are built to temporarily collect the increased stormwater runoff created in a developed residential or business area. The construction of homes, streets, sidewalks, driveways and buildings alters the natural landscape and decreases the surface area that previously soaked in water from rains and snow melt. As a result, stormwater runoff increases and can create issues with flooding and erosion. Where are detention basins located? Detention basins can be located on commercial and even private residential property. This can be a residential home or within a residential area maintained by a homeowners association (HOA).
Cooper Park
Basin responsibility. Who is responsible for the detention basin? Whether you are an individual property owner, an HOA representative or property manager, if the basin is on your property, the responsibility of the basin structure would be yours to maintain and ensure continual longterm operation. Routine maintenance will improve the performance and appearance, while also prolonging the life of the basin, keeping our community safe from flooding and our waterways clean.
STORMWATER: DETENTION BASIN • OPERATION & MAINTENANCE • 3 Know how to spot a basin. WHAT IS A DETENTION BASIN?
Types of Basins There are different types of basins to help with controlling stormwater. Some are designed to permanently hold a reservoir of water and others serve to collect stormwater, during increased rain and snow melt, in order to filter and slowly release into our waterways.
• Retention Basin, or wet detention basin, are designed to permanently hold a reservoir of water. They are essentially, man-made ponds built with vegetation around the perimeters in order to minimize or prevent erosion of the basin structure. Additionally, they provide flood control and water quality benefits. See page 6 for Vegetation Management.
• Water Quality Basin, or extended dry detention basins, are designed to collect stormwater during increased rain fall or snow melt and slowly release it, allowing debris and trash to settle or filter out before draining to a nearby waterway. This guide primarily focuses on these types of basins.
• Flood Control Basins are designed to reduce flooding downstream by holding stormwater and slowly releasing it. These basins do not provide a significant water quality benefit but can be retrofitted to do so. Anatomy of a Basin Concrete/ Trash Rack Grass Paved Surface
Water Detention Level Embankment Well Screen & Perforated Plate
Outlet Pipe Concrete Outlet Basin Floor Rock Pile Structure
*definitions listed on page 8
Think of it as a large bathtub... that holds the stormwater runoff from sidewalks, roads and parking lots after a heavy rain. The stormwater drains out of the basin much like it would in a tub; dirt and debris being held in the tub once the water drains is identical to how a basin allows trash, debris and pollutants to settle to the basin floor or filter out before being released into a nearby waterway.
Once a tub has been drained, the dirt and debris can be seen on the floor or as a ring of grime around the drain. As you would clean this out of a tub, those pieces of trash and debris in a basin would also need to be periodically removed and cleaned out.
STORMWATER: DETENTION BASIN • OPERATION & MAINTENANCE • 4 Keep your basin maintained. HOW TO CARE FOR A BASIN
Why is basin maintenance important? Properly maintained basins decrease the likelihood of pollutants reaching our waterways and minimize the potential for flooding and erosion. When a basin is not cared for it is not only a visual nuisance, but it can cause an array of issues to the surrounding area and waterways. Not to mention, the cost to repair a basin that no longer functions can be very expensive. Developing a maintenance plan Detention Basin Design When developing a maintenance regimen for a basin, it is ideal to obtain a copy of the basin design through a neighborhood homeowners’ association or by contacting our Stormwater Engineering Division by phone at 864.1935. Access Ensure proper access to the basin for regular inspection and maintenance activities. Identify access points that are wide enough for heavy equipment that may be needed for dredging or major repairs. Consider HOA prohibition against homeowners placing fences, outbuildings, landscaping or anything which might interfere accessing a basin for maintenance requirements. The access point may be within a drainage easement that prohibits placing structures within it. Record Keeping When performing maintenance tasks, remember to record all inspections, activities, repairs and associated costs. An inspection checklist has been provided at the end of this guide that can assist in future documentation of operations and maintenance. Costs of Maintaining An effective maintenance program will incur costs and detention basin owners should budget accordingly. Good record keeping can help to determine annual costs more accurately. Owners should set aside money for routine maintenance as well as the occasions when outside expertise or equipment is needed to maintain, upgrade or repair a basin. Conduct Routine Inspections For basins constructed after the adoption of the City’s Flood Control and Water Quality Protection Manual* a self-inspection must be submitted annually to the City. Submit completed inspections to the Water Quality Division by email to [email protected] or via standard mail to 290 E Central St. *The manual was adopted on December 11, 2017
Monthly Inspections Quarterly Inspections Annual Inspections • Remove trash, debris or yardwaste • Remove any considerable • Inspect structural components blocking the inlet(s), outlet(s) and sediment accumulation with and replace any that may be the basin floor. a shovel and wheelbarrow if broken or failing. preventing water flow. • Inspect for erosion and reseed • Replace rock pile if water flow any bare areas. is restricted from yardwaste and • Use inspection checklist to ensure sediment buildup. all components of basin are functional.
STORMWATER: DETENTION BASIN • OPERATION & MAINTENANCE • 5 Easy ways to get started. HOW TO CARE FOR A BASIN
Basic Housekeeping Tips Not everything involved in the care of a basin requires physical labor, tools or replacement parts. The best way to prolong the life of a basin is by performing simple daily practices such as:
Yardwaste Disposal: Lone Pine Recycling Center Leaves, grass clippings and brush should not 3020 S. Lone Pine Avenue be discarded in a basin. Instead, collect these Franklin Ave. Recycling Center. 731 N. Franklin Avenue and dispose of at one of the following: Large brush and and branches are only accepted at the Yardwaste Recycling Center Yardwaste Recycling Center. 3790 S. Farm Road 119, Brookline, MO
Yard Care Additives: Fertilizers should only be used if a soil test determines Fertilizers, pesticides and herbicides should that the area is in need of nutrients to promote grass be used in moderation in a detention basin. growth. Excess application of any products could wash off - adding pollution to our waterways. Pesticides and herbicides may be used to manage Contact James River Basin Partnership to see if you invasive species or convert the vegetation to natives. qualify for a free soil test. (417) 836.4847
Chemical Disposal: Vehicle liquids and oils should never be Pet Waste Disposal: discarded in a basin or open water source. Pick up and dispose of pet waste in the trash and never Contact the Household Chemical Collection Center at (417) 864.2000 to schedule an appointment for disposal. in or near a basin.
Vegetation management When Getting Your Thumbs Green is Necessary If the vegetation throughout a basin is not managed, issues can occur. Too much vegetation can reduce the storage capacity of the basin and cause flooding downstream. Here are some ways you can manage the vegetation and extend the life and performance of your basin:
• Mowing: The basin should be mowed regularly. The frequency may depend on desired aesthetics, visibility and proximity to neighbors. It should be mowed frequently enough to avoid weed complaints, per City Code: Article 7 Sec.74-401 through 74-404 which prohibits weeds over 7” in height, and to prevent woody plants from becoming established in areas they are not wanted.
• Dead Vegetation: At least once annually, all decomposing or dead vegetation should be removed, especially if it is interfering with or clogging pipe openings of the concrete outlet structure.
• Algae Control: Retention basins can have a tendency to accumulate algae as a result of water stagnation. Algae thrives off of nutrient-rich conditions. In turn, this can be harmful to wildlife. If you experience excessive algae growth, we recommend consulting a professional to assist in a program to identify, minimize and control the nutrient runoff to your basin.
• Invasive Removal: Invasive plants generally provide little benefit for wildlife or water quality. A seasonal inspection should be practiced to remove any identified invasive growth. If left unchecked, they can overtake and eliminate the benefits provided by native plantings.
• Native Plantings: Native plants are perfect additions, as they not only beautify a basin, but they are ideal for assisting to prevent erosion, collect, soak up and filter stormwater runoff. Find out more information about native plants by visiting yardethic.com
STORMWATER: DETENTION BASIN • OPERATION & MAINTENANCE • 6 Retrofits and enhancements HOW TO IMPROVE AN EXISTING BASIN
What Can You Do to Improve How Your Basin Looks & Functions? There are a variety of improvement opportunities that exist for existing detention basins. These are referred to as retrofits or enhancements because they include enhancing existing elements or adding, or retrofitting, components to a basin that did not exist previously. When planning for a retrofit, or enhancement, consider the potential improvements that can be provided to stormwater quality, pond habitat and the aesthetics of the basin. Common improvements that you may consider, include:
• Outlet structure modifications. There have been improvements in the performance and functionality of newer detention outlets. Enhancements to an existing structure can provide extended detention of smaller storm events, improving downstream water quality.
• New or enhanced vegetative filter strips. Native plantings in these filter strips offer increased water absorption and pollution filtering within the basin.
• Additional tree plantings. Planting of trees in a dry detention basin can increase water absorption. Maintenance should be considered before planting as the leaves from the trees could play a role in clogging the outlet structure if left on the basin floor. Trees can also be planted around the perimeter of wet detention basins to reduce the water temperature - helping to prevent excess algae growth. Do not plant trees on a berm as they could cause structural damage.
*Any structural modifications need to be approved by the City and go through the planning and permitting system. Addition of native Starting a project plantings and tree plantings do not need to go through this process. Inventory First, you should determine a basin maintenance plan (see page 5). Once that is scheduled, goals and outcomes of the project should be considered and fully understood. These goals will help to identify considerations for site specific retrofit improvements. Evaluation Once improvement considerations are selected for consideration, conduct an evaluation of feasibility. The following questions should be answered: • Is there enough space? • Is it cost prohibitive? • Does the landscape impede implementation? • Do existing structures impede implementation? • Are the resources available to properly maintain? Drury Retrofit Basin Improvements Planning A great before and after example of a basin retrofit project is on the Goals and outcomes are outlined, considerations Drury University campus. On the left, the basin had a more direct are evaluated and specific improvements have been channel from the inlet to the outlet. When improvements were considered and made, the following construction was performed: determined. At this point, it is time to start a project. • Removed concrete channels • Increased infiltration Visit ecity.springfieldmo.gov/start-project • Lengthened and Increased flow path • Taller vegetation planted and to take the next steps towards scheduling your project. (visible by winding rock channel) allowed to grow
STORMWATER: DETENTION BASIN • OPERATION & MAINTENANCE • 7 Know your stormwater definitions. GLOSSARY OF WORDS & TERMS basin floor riser pipe An area of land at the bottom of the basin where A vertical pipe in a basin. Generally a long tube made of stormwater collects and is sloped to drain into an outlet. plastic or metal with holes drilled in it and designed to slowly release water. berm An earthen structure that acts as a wall of the detention rock pile basin. These structures hold the stormwater in the Also called rip-rap, these are man-placed rocks used to detention basin. assist with preventing erosion and filtering of additional pollutants from runoff. channel An area eroded or constructed where a concentrated flow runoff of water passes. Rainwater or snowmelt that would generally soak back into the ground or evaporate but is unable to infiltrate into detention basin the ground and runs off of the surface, i.e., land, building, A stormwater control that holds and controls stormwater pavement, etc. flow to reduce peak stormwater flows and minimize velocities to reduce erosion. They can also promote sediment settling of suspended pollutants. Created through erosion or wearing of the ground. Consists of dirt and rock particles that can be carried by embankment water, deposited and built up in basins and channels. see berm stormwater erosion see runoff The loss of sediment by moving water over a period of time. stormwater control measures (SCM) A term used to describe detention basins and other extended dry detention basin controls designed to manage the flow and quality of A type of detention basin designed to hold stormwater long stormwater runoff. enough for pollutants to settle out, typically 24-48 hours. spillway flood control basin An area of the detention basin where the flow during a A type of detention basin designed to prevent flooding. large storm event can leave the basin. inlet trash rack An area where stormwater can enter the basin — this A feature of an outlet, made of metal, that prevents debris could be a pipe, curb opening, channel or sheet flow. and trash from leaving the detention basin to prevent outlet structure blockages in downstream pipes and channels and protect water quality. Typically a concrete structure within the basin that has openings to regulate the flow of stormwater leaving the basin. vegetative filter strip perforated plate Densely vegetated landscaped areas designed to filter pollutants while reducing and treating runoff from A metal sheet with small holes that controls flow leaving adjacent pervious and impervious areas. the basin. This design should allow the water to drain in 24-48 hours. weir resuspension A control feature of an outlet control structure which is a rectangular or triangular notch that regulates the flow of Renewed suspension of a sediment, like mud, from the stormwater through the structure. bottom of a body of water. retention basin well screen A filtering device that keeps debris from clogging the A basin with a permanent pool of water that utilizes perforated plate. vegetation to help prevent erosion on the perimeter of the basin. Also called a wet detention basin. rills A shallow channel cut in the ground by running water.
STORMWATER: DETENTION BASIN • OPERATION & MAINTENANCE • 8 It’s time to inspect your basin. INSPECTION CHECKLIST
What is required during your basin inspection? We recommend that you print off pages eleven and twelve (can be two-sided) and fill-out during the on-site inspection. Be sure to have a phone or camera so that pictures can be taken of specific structures as noted on the checklist and the first bullet below. Once completed, follow directions below to submit your detention basin checklist. Follow these steps to complete your checklist:
• Photographic Documentation. A minimum of three photos should be taken of the following: inlet(s), the entirety of the basin and the outlet structure - regardless of condition. Any areas rated as a 1 or 2 should have additional photo documentation. All photographs should be clearly visible. Photo preference would be .jpg files sized at least 300px x 300px in dimension. This can generally be referenced in the file info on your computer or phone.
• Complete Inspection. Please follow and answer all sections of the inspection thoroughly and to the best of your ability before submitting.
• Submit Inspection. For basins constructed after the adoption of the City’s Flood Control and Water Quality Protection Manual, a self-inspection must be submitted annually to the City. Submit completed inspections to the Water Quality Division by email to [email protected] or via standard mail to 290 E Central St.
• Questions? Call (417) 864.1944
STORMWATER: DETENTION BASIN • OPERATION & MAINTENANCE • 9
City Code Chapter 96 Article I 96-14 City of Springfield, Department of Environmental Services: 290 E Central St Springfield, MO 65802 (417) 864-1944 Stormwater Operation and Maintenance Inspection Checklist: Detention Basin
Inspector Name and Title: Date of Inspection: Property Address: Owner Name: Owner Address: Owner Phone: Owner Email:
0 – Good Condition 1 – Degraded Condition 2 – Serious Condition Circle a score (0,1 or 2 for each area/row) Should monitor and continue routine Routine maintenance or repair needed. Functionality Immediate need for maintenance or repair to restore maintenance could be affected if not addressed functionality TRASH/DEBRIS/SEDIMENT REMOVAL
INLET: Trash/debris/sediment accumulation is visually Stormwater cannot enter the detention basin as There is no accumulation of trash, debris or Is there excessive trash/debris/sediment unpleasant and/or could be preventing stormwater designed because of the trash/debris/sediment sediment at the inlets. accumulation where stormwater enters the basin? from entering the basin as designed. accumulation at the inlets.
BASIN FLOOR: There is no accumulation of trash, debris or Trash/debris accumulation is visually unpleasant Trash/debris accumulation is a nuisance and/or the Is there excessive trash/debris/sediment sediment in the basin that is altering the storage and/or the sediment accumulation has decreased sediment accumulation has significantly decreased the accumulation in the basin area? capacity of the detention basin. storage capacity of the basin. storage capacity of the detention basin.
Trash/debris/sediment accumulation is completely OUTLET: Trash/debris/sediment accumulation is preventing There is no accumulation of trash, debris or blocking the outlet structure and preventing Is trash/debris/sediment accumulation hindering sediment that could prevent stormwater from stormwater from leaving the detention basin as stormwater from leaving the detention basin as stormwater from leaving the basin as designed? leaving the detention basin. designed. designed. EROSION INLET: There is minor erosion (less than 6 inches deep) at There is significant erosion (deeper than 6 inches) at Is there evidence of erosion where stormwater enters The inlets are stable with no existing erosion. one or more inlets. one or more inlets. the basin?
BASIN FLOOR: There is no existing erosion in the detention There is significant erosion (deeper than 6 inches) in There are small rills forming in the detention basin. Is there evidence of erosion on the floor of the basin? basin. the detention basin.
Erosion around the outlet structure is significant OUTLET: Rills or minor erosion are present around the outlet There is no erosion around the outlet structure. (deeper than 6 inches). It may be causing a structural Is there evidence of erosion around the outlet? structure. failure or creating a safety hazard.
STORMWATER: DETENTION BASIN • OPERATION & MAINTENANCE • 11 Operation and Maintenance Inspection Checklist: Detention Basin Page 2
MOWING/VEGETATION MAINTENANCE
All of the trees and/or shrubs have died, been damaged Some of the trees and/or shrubs have died, been ENTIRE BASIN: and/or removed. If they were required as part of a Trees and shrubs are in good condition. damaged or removed from the detention basin. Condition of trees or shrubs (if present) buffer yard or water quality credit. If not required, Replacement should be considered. consider replanting due to tree benefits.
ENTIRE BASIN: The bottom of the detention has less than 70% grass Grass and vegetation covers the entire bottom of There is 70% grass growth in the basin but there are Does vegetation uniformly cover at least 70% of the growth. The basin needs to be reseeded/revegetated the detention basin. bare patches that should be reseeded. basin (i.e. no large bare areas)? immediately.
STRUCTURAL MAINTENANCE
The embankment or berm has settled and created a The berms and embankments are stable or there is AROUND BASIN: partial spillway which is causing the basin to function minor settling occurring in areas that would not N/A Have the berms/embankments settled? differently than designed. The embankment needs to be affect the functionality of the basin. raised to the original design height immediately.
INLET: The structural components of the basin inlets have The inlet structures are in good condition and The structural components of the basin inlets are Condition of structural components such as the curb failed and are creating a safety hazard and/or causing there are no structural failures. cracked or broken but not affecting functionality. openings, pipes, etc. the basin to not function as designed.
BASIN FLOOR: The structural components of the basin have failed and The structural components of the basin are cracked or Condition of structural components such as concrete The structural components are in good condition. are creating a safety hazard and/or causing the basin to broken but not affecting functionality. channel not function as designed.
OUTLET: Outlet structure has failed and is preventing the Condition of structural components such as the Outlet structure is in good condition and has no The structural components of the basin outlet are detention basin from functioning as designed (this concrete outlet box, concrete weir, metal trash rack, structural failures. cracked or broken but not affecting functionality. includes any unreported modifications to the structure). or perforated metal plate.
Inspection Comments:
This inspection form and inspection photos* should be turned in to Sarah Davis at [email protected] or 290 E Central St Springfield, MO 65802 *A minimum of three photos should be taken of the following: inlet(s), the entirety of the SCM and the outlet structure regardless of condition. Areas rated as 1 or 2 should have additional photo documentation.
STORMWATER: DETENTION BASIN • OPERATION & MAINTENANCE • 12