Stormwater Design Standards
The Stormwater Design Standards can be found in Chapter 2 of the Riverton City Standards Specifications and Plans.
Low Impact Development (LID) standards 

Water resources both surface and subsurface can be significantly impacted by development of all types including Riverton’s local rivers, creeks, and streams.  Responsible and sustainable development is important to Riverton City, we are committed protecting our water ways and remaining compliant with State and Federal environmental regulations.
The principle behind the LID regulation is to mimic natural hydraulic and geologic processes as much as reasonably possible.  Before development especially modern urban development a significant portion of precipitation infiltrates back into to the ground and much of the excess runoff is filtered by plants essentially pre-treating the runoff before reaching surface and groundwater resources.  Much of modern urban development drainage systems significantly by passes these natural processes resulting in increased flooding and polluted water resources that affect everybody.  
Reference regulation can be found mostly in sections 3.2 and 4.2.5 of the Municipal Separate Storm Sewer System Permit (MS4):  

Flood and Water Quality Standard Details for Publicly Maintained Roadways
To adequately manage runoff, cost and liability of public roads the City must hold to standards.   The standard approach is based on mimicking natural processes by pre-treating runoff using plants to capture and remove urban pollutants.  The excess retention and flood volume is then managed below and or on the surface.  There are five main standard variations depending on development choice and site conditions.  The City understands unique site conditions can justify some variations, but the principles behind sound flood and water quality control should remain constant, but ultimately development should be expected to manage their own project impact onsite and downstream. 

 

Reverse Pan Type D curb Swale Drywell General Standard
This standard is intended for public residential roadways.  This system does not require storm drain pipe, additional land dedication for conventional detention or retention ponds and does a good job at distributing the runoff impact across a large area as nature did previously.  The roadway and drywell are maintained by the City and the property owner maintains the park-strip just as they do with park strips today. 

 

Reverse Pan Type D curb Swale Drywell Dual System Retention Pond Standard.
This standard is intended for public residential roadways but allows development choice of separating the excess flood volumes from the retention volumes.  It also accounts for levels of infeasibility where portions or all runoff cannot be retained.  Pocket ponds must be located on private property with a public easement and the owner or HOA must enter into a long-term stormwater management agreement with City.  Ponds qualifying for public ownership and maintenance must comply with Park Department requirements. 

 

Reverse Pan Type D curb Swale Drywell Dual System Detention Tank Standard.
This standard is intended for public residential roadways but allows development choice of separating the excess flood volumes from the retention volumes by detaining excess flood volume in underground tanks for release to City storm drain system.  It also accounts for levels of infeasibility where portions or all runoff cannot be retained

 

Reverse Pan Type D curb Swale Drywell Dual System Detention Pond Standard.
This standard is intended for public residential roadways but allows development choice of separating the excess flood volumes from the retention volumes by detaining excess flood volume in above ground ponds.  It also accounts for levels of infeasibility where portions or all runoff cannot be retained.  Pocket ponds must be located on private property with a public easement and the owner or HOA must enter into a long-term stormwater management agreement with City.  Ponds qualifying for public ownership and maintenance must comply with Parks Department requirements.

 

Traditional Detention/Retention Pond Systems.
This standard is intended for public residential roadways.  It consist of traditional drainage infrastructure, including; high back curb, inlets, pipe, retention drywells and detention or retention ponds.  Pocket ponds must be located on private property with a public easement and the owner or HOA must enter into a long-term stormwater management agreement with City.  Ponds qualifying for public ownership and maintenance must comply with Parks Department requirements.

 

Low Impact Development for private development
This includes flood and Water Quality infrastructure and management for commercial, industrial, institutional and private residential subdivisions.  Flood and water quality infrastructure can vary but must conform to the minimum flood and water quality criteria as with public infrastructure and per the Standard Specifications and Plans.  In addition to flood and water quality control, these systems must be maintainable and perform equally with the public infrastructure.  The following links are local resources for reference.  


To comply with the Clean Water Act the City encourages development to reduce their runoff impact by retaining all or a portion of runoff.  Development that conforms to this approach can receive up to a 45% reduction of their Stormwater Utility Fee.  Stormwater Utility Fee Adjustments may be apply for by application.  
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