Last Updated 03/07/2024
Excerpt- Storm Drainage Design Criteria
Chapter 1 - Purpose
The purpose of this manual is to provide the minimum standards to be used for the analysis and design of storm drainage systems for private development projects and City contracted projects within the City of Sheridan. These standards apply both to new development as well as improvements within existing developments. Design criteria and methods other than those described in these design standards shall be applied only after requesting and receiving approval from the Public Works Department.
Chapter 2 – Drainage Report Submittal Requirements
A Preliminary Drainage Report shall be prepared by a registered Civil Engineer acting on the Owner’s behalf. All drainage reports must include the design calculations necessary to support the proposal. Drainage reports shall incorporate the following in approximately this format:
- Provide a brief project summary including the location, description of the existing property and the proposed development, a discussion of surrounding developments, and the proximity to floodplains.
- Provide a detailed figure for the existing site conditions and a detailed figure for the proposed site conditions that show site boundary, topographic contours, basin/sub-basin area boundaries, drainage structures, wetlands, sensitive area buffers and setbacks, easements, etc. State on each figure the total area and the amount of pervious and impervious area in each
basin/subbasin area. Show flow paths with slope, flow type, surface type, and run length. - Describe existing conditions including structures, drainage basins, flow paths, pervious/impervious areas, slopes, vegetation/land use, soil type, runoff curve numbers (CN), time of concentration and other runoff characteristics as well as upstream offsite flow contributions, downstream offsite capacity analysis, and existing drainage problems.
- Describe proposed developed conditions including, drainage basins, flow type and flow paths, pervious/impervious areas, slopes, vegetation/land use, CNs, time of concentration and other runoff characteristics as well as upstream offsite flow routing, detention or retention storage volume, release rates, overflow route capacity, and proposed storm drainage system.
- Describe applicable State or Federal regulations, design standards, design storm frequencies, as well as hydrologic and hydraulic methods of analysis.
- State runoff control design assumptions and describe method of analysis.
- Appendix: Provide any calculations and figures necessary to support the proposed design, including basin characteristics, time of concentration, weighted Curve Numbers (CN), percent impervious area, runoff hydrograph generation, stage-discharge and stage-storage tables for detention routing, conveyance system capacity calculations, floodplain maps, applicable excerpts from previous reports, correspondence with adjacent property owners, ditch companies, utility companies, or regulatory agencies, or other information necessary to fully document the drainage plan.
Three copies of the Preliminary Drainage Report shall be submitted to the City of Sheridan for review. The City Public Works Department will return one copy with comments and suggested revisions to the applicant. The applicant shall revise the Preliminary Drainage Report and submit three copies of the Final Drainage Report along with the Storm Drainage Construction Plans and Details for final review.
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Frequently Asked Questions
What are the most common compliance failures?
Based on AQUALIS’s experience conducting thousands of inspections across the country, the most frequent compliance issues we encounter are:
Overgrown vegetation: Pond banks, swales, and bioretention areas where vegetation has overtaken the designed system, reducing capacity and blocking outflow structures.
Sediment accumulation: Detention ponds lose capacity over time as sediment builds up. Most systems require periodic dredging; many owners don’t realize a pond has lost 30%–50% of its storage until a flood event reveals the problem.
Clogged or damaged inlets and outlets: Debris-blocked catch basins and outlet structures are among the most common findings on inspections and among the easiest to prevent with routine maintenance.
Missing or incomplete records: Inspection reports not filed, maintenance logs not kept or Operation and Maintenance Agreements not recorded with the county register, all common findings that create regulatory exposure even when the physical system is functioning correctly.
Structural deterioration: Cracked or collapsed pipes, eroded embankments and damaged concrete structures that have gone unrepaired past the point of simple fixes.
Illicit discharges: Non-stormwater connections to the drainage system (from wash water, sanitary lines or industrial processes) that violate NPDES permit conditions.
How often do I need to have my stormwater system inspected?
Inspection frequency varies by state, permit type and the type of stormwater infrastructure on your property, but most jurisdictions require at least one inspection per year. Many municipalities require annual inspections conducted by a licensed professional engineer, with a signed report submitted to the local stormwater authority.
Some permits impose more frequent requirements: construction sites under an active NPDES permit are typically inspected before and after significant storm events. Properties in sensitive watersheds or with a history of violations may be subject to additional oversight.
How does stormwater impact property value?
Stormwater infrastructure affects property value in several ways that are easy to overlook until a transaction is underway.
During due diligence: Buyers and lenders increasingly request stormwater inspection reports as part of commercial property transactions. A system with deferred maintenance, unresolved NOVs or missing inspection records can become a negotiating issue or a deal risk.
Flooding history: Properties with recurring stormwater problems (parking lot flooding, pond overflows, erosion) carry a documented liability that affects both insurability and perceived value.
Remediation costs: Deferred stormwater maintenance compounds over time. A pond that costs a few thousand dollars to maintain annually can require $50,000–$200,000 in dredging or reconstruction if neglected for several years. These costs are often surfaced during appraisals or environmental assessments.
Curb appeal and aesthetics: For retail and multifamily properties, a well-maintained stormwater pond or green infrastructure feature is an amenity. An overgrown, silted-up pond signals neglect to tenants and customers alike.
What is stormwater compliance?
Stormwater compliance means meeting the federal, state and local regulations that govern how rainwater and snowmelt runoff is managed on your property. For most commercial, industrial and multifamily properties, compliance involves maintaining on-site stormwater infrastructure (ponds, catch basins, drainage pipes), meeting inspection requirements and keeping records that demonstrate your system is functioning correctly. The specific requirements depend on your state, municipality and the type of permit that applies to your property.
Why is stormwater maintenance important?
Stormwater systems are designed to manage a specific volume and velocity of water. When they’re not maintained, performance degrades and the consequences can be significant:
Regulatory risk: A failed inspection or malfunctioning system can result in a Notice of Violation (NOV), fines and mandated repairs under a regulatory timeline, often more costly than routine maintenance would have been.
Property damage: Clogged inlets, deteriorated pipes and overwhelmed ponds lead to flooding, erosion and structural damage to pavement and buildings. Sinkholes caused by failed underground infrastructure are a common and expensive result of deferred maintenance.
Environmental liability: Untreated runoff carrying pollutants into waterways can expose property owners to broader environmental enforcement, including from state environmental agencies and the EPA.
Permit renewal risk: Many stormwater permits require demonstrated compliance history at renewal. Gaps in maintenance records can complicate or delay renewal.
Who is responsible for stormwater compliance?
In most cases, the property owner is legally responsible for maintaining stormwater control facilities on their land and ensuring those systems remain in compliance with applicable permits. For commercial properties with active construction or industrial operations, responsibility may also extend to the site operator or contractor, who must comply with any NPDES permit tied to their activity. If you own or manage property with stormwater infrastructure (detention ponds, bioretention areas, underground systems or drainage structures) compliance is your obligation regardless of whether your tenants are the ones generating runoff.
AQUALIS can serve as your compliance partner, handling inspections, maintenance, and regulator communication on your behalf.
Can stormwater fees be reduced?
Yes—many municipalities offer stormwater fee credits or reductions for property owners who actively manage runoff on-site and reduce the burden on public stormwater infrastructure. Credit programs vary by jurisdiction but commonly recognize:
On-site detention or retention: Ponds, underground vaults, and other systems that hold and slowly release stormwater can qualify for volume-based fee reductions.
Green infrastructure: Bioretention areas, permeable pavement, green roofs and native landscaping may qualify for additional credits in municipalities that incentivize water quality improvements.
Documented maintenance: Some programs require proof of regular inspections and maintenance to retain credits — meaning a lapsed maintenance program can result in losing a credit you’ve held for years.
AQUALIS can review your property’s eligibility for local stormwater credit programs and help prepare the documentation required to apply or maintain credits. Savings vary widely by municipality but can offset a meaningful portion of annual fee assessments.
The information on this page is provided for general informational purposes only and is not legal advice. Regulations change frequently — AQUALIS makes no warranty as to the accuracy or completeness of this content, and any reliance on it is at your own risk. Consult a qualified professional or your local regulatory authority to confirm requirements applicable to your specific property.
