450 Stormwater Management
400 Mapping and Regulations

450
Stormwater Management

Stormwater management plays a crucial role in planning around floods. How water is channeled and directed during flood events is driven by your community's urban fabric. As such, this activity awards points for regulating development to account for stormwater management considerations.

452.a
Stormwater management regulations (SMR)

You can receive credit for implementing stormwater management regulations that help reduce runoff caused by development.

Level of effort = moderate

Overview

Credits are awarded under this element for implementing regulations that involve stormwater detention/retention or promote low impact development. In addition to regulating, your community must also maintain stormwater management infrastructure. This can be a bit more challenging for some communities.

Credits are divided in four subelements: SZ, DS, LID, and PUB.

  • SZ: To receive credit, you must regulate the development of 5 acres or more, or increases in impervious area of 20,000 sq feet or more.
  • DS: You can get full DS credit for requiring that all water discharges up to and including the 100 year storm must be released at rates that do not exceed the pre-development peak discharge (for a development or an entire region). An additional 75 credits can be awarded for regulating the retention of all runoff caused by a new development.
  • LID: You can also receive credit for requiring low impact development techniques for new developments (examples include rainwater cachement, preservation, etc...)
  • PUB: Credits are awarded for requiring the maintenance of stormwater management facilities. This maintenance can include allowing your community to inspect facilities and require the owner to perform or pay for needed maintenance, or requiring new facilities to be deeded to your community. Your community must have legal authority to enforce this subelement.

You may receive credit for requiring fees in lieu of stormwater management facilities if the fees fund facilities that were/are built before the development.

Considerations

Many communities already regulate stormwater management in new developments so this element might require minimal effort.

Documentation

To receive credit for this element, you must provide:

  • A copy of the regulation, with each relevant section called out
  • Drainage reports showing the enforcement of the regulations
  • Documentation that nearby communities use similar regulations (if the watershed spans communities)
  • An impact adjustment map showing the regulated area and the total watershed

Credit Calculation

Max = 380 for the following:

Element Minimum Credits
SZ - Regulating all development 110
SZ - Regulating all development except single family homes, parcels measuring a half acre or less, or impervious area of 5,000 sq ft or less 90
SZ - Regulating all development except parcels of 1 acre or less, or impervious area of 10,000 sq ft or less 60
SZ - Regulating all development except parcels of 5 acres or less, or impervious area of 20,000 sq ft or less 15
DS1a - Designing water detention for a 10 year storm, OR 14
DS1b - Designing water detention for a 10 year storm and controlling water volume 21
DS2a - Designing water detention for a storm between 10 and 100 years, OR 36
DS2b - Designing water detention for a storm between 10 and 100 years and controlling water volume 54
DS3a - Designing water detention for a 100 year storm, OR 100
DS3b - Designing water detention for a 100 year storm and controlling water volume 150
LIDa - Requiring all new development to use low impact development techniques to control runoff 25
LIDb - If SZ=90 20
LIDc - If SZ=60 15
LIDd - If SZ=15 10
PUB - Requiring inspection and maintenance of stormwater management facilities 20

The impact adjustment for this element is calculated as follows:

Area impacted by stormwater regulations / Total watershed area

For this calculation, you do not have to include the upstream portion of watersheds that exceed 50 square miles, areas protected by flood control structures, or areas not likely to be developed in the total watershed calculation.

If the impact adjustment is less than 0.15, then communities can use 0.15 for the ratio.

452.b
Watershed master plan (WMP)

Does your community have a watershed master plan?

Level of effort = highPart of this element is required for CRS Class 4

Overview

Your community can receive credits for implementing stormwater management regulations using a watershed master plan. You also get credit for evaluating future conditions, looking at more frequent and longer storms, evaluating sea level rise and climate change, identifying wetlands and other natural areas, protecting natural channels, and identifying a funding source to implement the plan.

To qualify for credits under this element, your plan must model hydrologic behavior throughout the watershed, examine current and future conditions, and provide mitigation recommendations for reducing risk in the watershed. At least one watershed must be modeled and the model(s) should consider the 100 year storm or evaluate sea level rise projections during multiple storm events. Considering a 100 year storm and/or sea level rise is a prerequisite for Class 4. Your community must also adopt regulatory standards requiring stormwater management of runoff from a 25 year flood event. The plan should be evaluated every 5 years. There are 8 subelements for this element, they are detailed here in the "Credit Calculation" section.

Documentation

To get credit for this element, you must provide:

  • Documentation of plan adoption
  • A copy of the watershed master plan with subelements labeled
  • The Stormwater management regulations (SMRs)
  • For WMP8, copies of the ordinance and first fiscal year budget
  • Every 5 years, an evaluation report or letter should be provided from an engineer that addresses future conditions, precipitation data, methodology, new construction, and other factors
  • An impact adjustment map showing the regulated area and the total watershed
  • Documentation that nearby communities use similar regulations (if the watershed spans communities)

Credit Calculation

Max: 315, for the following:

Element Maximum Credits
WMP1 - If the watershed master plan meets all requirements (prerequisite for all of the following elements) 90
WMP2 - If the plan includes managing the runoff of all storms up to the 100 year storm 30
WMP3 - If the plan include providing onsite management of future stormwater, so that no new developments result in increases in peaks or volumes 55
WMP4 - If the plan includes managing runoff from all storms up to and including the 5 day event 35
WMP5 - If the plans identifies open space areas to be preserved for stormwater management purposes 30
WMP6 - If the plan recommends that protecting natural channels and your community adopts a corresponding ordinance 25
WMP7 - If the plan recommends channel improvement projects use natural approaches and your community adopts an ordinance stating this 25
WMP8 - If the plan identifies a funding source to implement the plan 25

The impact adjustment for this element involves dividing the area impacted by the watershed master plan by the area of the watershed.

Area impacted by watershed master plan / Total watershed area

If the impact adjustment is less than 0.15, then communities can use an Optional Minimal value of 0.15 for the ratio.

452.c
Erosion and sedimentation control regulations (ESC)

Is your community implementing regulations for erosion and sedimentation control?

Level of effort = moderate

Overview

Pollution associated with sedimentation is a particular concern when land is shifted during construction work. Because of this, you can receive credits for requiring erosion and sediment control measures for land undergoing development. For credits to be awarded, your community must require these measures for all construction sites, including buildings, roads, regrading, or other activity that disturbs land.

Documentation

To receive credits for this element, you must provide:

  • The regulation or ordinance that identifies an office or person responsible for compliance and enforcement measures
  • Permit records that show the enforcement of the regulation

Credit Calculation

Max: 40 for one of the following:

Element Maximum Credits
ESC1 - Regulating erosion and soil loss from land greater than 1,000 sq ft, OR 40
ESC2 - Regulating erosion and soil loss from land greater than half an acre OR 30
ESC3 - Regulating erosion and soil loss from land greater than 1 acre 10

There is no impact adjustment for this element.

452.d
Water quality regulations (WQ)

Water quality regulations can have a large-scale, lasting impact on your overall stormwater management system.

Level of effort = moderate

Overview

Beyond regulating during construction, your community can receive credit for protecting water quality as a permanent part of your stormwater management system. This can be done by requiring developers to implement measures that clean stormwater, such as grass filter strips, infiltration trenches, and bioswales. To receive credits, you must require new developments of one acre or more to implement measures to improve the quality of stormwater.

Documentation

To document your work for this element, you must provide:

  • The applicable regulation or ordinance
  • Permit records that demonstrate enforcement of the regulation

Credit Calculation

Max: 20

There is no impact adjustment for this element.

This CRS guide was produced by CRS professionals and Certified Floodplain Managers to help you navigate the Community Rating System. It is not meant to replace FEMA's official CRS Coordinator's Manual, nor should it supersede the instructions given by your ISO/CRS Specialist.

For additional resources, visit https://crsresources.org/ .