Step 3. Climate/Regional Factors


Both the design characteristics and the best practice for a site can be influenced by regional factors such as the topography, geography, or climate of a region. The following matrix identifies five regional factors, including:

Arid/ Semi-Arid. In these dry climates, the water conservation concerns may eliminate some practices from consideration. Furthermore, practices need to be designed to reflect the challenges in these regions.

Low Relief. In areas of low relief, particularly those that are in coastal regions, STPs that require minimal head and distance to groundwater are preferred.

Cold Climates. In cold climates, practice selection or design needs to incorporate features to deal with challenges such as winter snowmelt and frost heave.

Karst Topography. Areas of karst topography presents specific challenges to STP designers, including potential groundwater contamination and sinkhole formation.

High Rainfall. Regions that receive high annual rainfall, and particularly those areas that experience frequent hurricanes, make application of some practices challenging.

This matrix will likely not appear in its entirety in many Stormwater Design Manuals. If a manual is designed for a state, they may have some distinct climate zones, or areas of karst topography. Furthermore, a STP manual writer may choose to make finer distinctions, based on specific climate zones within a state.

Matrix 3. Climate/ Regional Factors
Stp Group Arid/ Semi-arid Low Relief

(E.g., Coastal)

Cold Climates Karst Topography High Rainfall
Ponds Conduct a water balance analysis. Supplemental water may be necessary. Pond drain may not be feasible. Incorporate design features to improve winter performance. Encourage use of a clay liner to prevent sinkhole formation, infiltration of hotspot runoff.

Conduct geotechnical tests to ensure that sinkholes do not form.

Allow a maximum ponding depth of no greater than 4 feet to reduce the risk of sinkhole formation.

Wetlands Restricted use due to water supply.


Encourage the use of salt-tolerant vegetation.
Infiltration OK Check distance to GW table Incorporate features to minimize the risk of frost heave.

Discourage infiltration of chlorides.

For Karst where sinkholes may form, discourage use.

For other Karst, encourage heavy pretreatment.

May require more frequent maintenance due to increased organic build-up in moist soils.
Filters OK Perimeter Sand Filter is best option Incorporate design features to improve OK OK
Open Channels Select drought-tolerant vegetation. Ensure minimum slope can be achieved. Encourage the use of salt-tolerant vegetation. Carefully analyze infiltration when sink holes are a Ensure a thick vegetative cover to reduce the risk of channel

While most climatic issues can be resolved with guidance, regulatory requirements should be in place to prevent groundwater contamination and sinkhole formation in karst regions.