University of New Hampshire Stormwater Center (UNHSC)

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University of New Hampshire

University of New Hampshire
University of New Hampshire Scholars' Repository
UNH Stormwater Center Research Institutes, Centers and Programs
2-1-2017
Regular Inspection and Maintenance Guidance for
The Subsurface Gravel Wetland Stormwater
Management Device
University of New Hampshire Stormwater Center (UNHSC)
Follow this and additional works at: https://scholars.unh.edu/stormwater
This Article is brought to you for free and open access by the Research Institutes, Centers and Programs at University of New Hampshire Scholars'
Repository. It has been accepted for inclusion in UNH Stormwater Center by an authorized administrator of University of New Hampshire Scholars'
Repository. For more information, please contact nicole.hentz@unh.edu.
Recommended Citation
University of New Hampshire Stormwater Center (UNHSC), "Regular Inspection and Maintenance Guidance for The Subsurface
Gravel Wetland Stormwater Management Device" (2017). UNH Stormwater Center. 17.
https://scholars.unh.edu/stormwater/17
 
Regular Inspection and Maintenance Guidance for  
The Subsurface Gravel Wetland Stormwater Management Device 
Regular inspection and maintenance is critical to the effective operation of Subsurface Gravel 
Wetland (SGW) systems. It is the responsibility of the owner to maintain the SGW in accordance 
with the minimum design standards. This page provides guidance on maintenance activities that are 
typically required for these systems, along with the suggested frequency for each activity. Individual 
systems may have more, or less, frequent maintenance needs, depending on a variety of factors 
including but not limited to: the occurrence of large storm events, overly wet or dry periods, regional 
hydrologic conditions, and the upstream land use. 
ACTIVITIES 
The most common maintenance activity is the removal of sediment and organic debris from the 
system and bypass structures. Visual inspections are routine for system maintenance. This includes 
looking for standing water, accumulated leaves, holes in the soil media, signs of plant distress, and 
debris and sediment accumulation in the system. Vegetation coverage is integral to the performance 
of the system.  A SGW system is a subsurface horizontal filtration system and does not rely on 
surface soil infiltration capacity for treatment. As such, surface infiltration rates are expected to be 
low and not a criterion for cleaning. Rather, stormwater access to subsurface treatment is by way of 
a hydraulic inlet.  It is important to ensure these inlets are performing properly.  
ACTIVITY FREQUENCY 
CLOGGING AND SYSTEM PERFORMANCE 
Inspect inlets and outlets to ensure good condition and no evidence of 
deterioration. Check to see if high-flow bypass is functioning. 
   Remedy: Repair or replace any damaged structural parts, inlets and outlets.  
Clear or remove debris or restrictions.  Annually, more 
frequently in the 
first year of 
operation 
 
Check for internal erosion, evidence of short circuiting, and animal burrows. 
   Remedy: Soil erosion from short-circuiting or animal boroughs should be 
repaired when they occur.  
Check that the system is fully draining within a 24 - 48 hour period after rain 
events  
   Remedy: Repair or restore hydraulic inlet or outlet function. 
VEGETATION 
Check for robust vegetation coverage throughout the system and dead or dying 
plants. 
   Remedy: Vegetation should cover > 75% of the system and should be 
reseeded and cared for as needed.    
Annually or as 
needed 
Cut and remove vegetation from the Gravel Wetland System and forebay in 
order to maintain nitrogen removal performance. 
   Remedy: The vegetation should be cut and removed from the system to 
prevent nitrogen from cycling back into the system. 
Once every 3 years 


Regular Inspection and Maintenance Guidance for
 The Subsurface Gravel Wetland Stormwater Management Device

UNH Scholars' Repository

University of New HampshireUniversity of New Hampshire Scholars' RepositoryUNH Stormwater Center Research Institutes, Centers and Programs2-1-2017Regular Inspection and Maintenance Guidance forThe Subsurface Gravel Wetland StormwaterManagement DeviceUniversity of New Hampshire Stormwater Center (UNHSC)Follow this and additional works at: https://scholars.unh.edu/stormwaterThis Article is brought to you for free and open access by the Research Institutes, Centers and Programs at University of New Hampshire Scholars'Repository. It has been accepted for inclusion in UNH Stormwater Center by an authorized administrator of University of New Hampshire Scholars'Repository. For more information, please contact nicole.hentz@unh.edu.Recommended CitationUniversity of New Hampshire Stormwater Center (UNHSC), "Regular Inspection and Maintenance Guidance for The SubsurfaceGravel Wetland Stormwater Management Device" (2017). UNH Stormwater Center. 17.https://scholars.unh.edu/stormwater/17 Regular Inspection and Maintenance Guidance for  The Subsurface Gravel Wetland Stormwater Management Device Regular inspection and maintenance is critical to the effective operation of Subsurface Gravel Wetland (SGW) systems. It is the responsibility of the owner to maintain the SGW in accordance with the minimum design standards. This page provides guidance on maintenance activities that are typically required for these systems, along with the suggested frequency for each activity. Individual systems may have more, or less, frequent maintenance needs, depending on a variety of factors including but not limited to: the occurrence of large storm events, overly wet or dry periods, regional hydrologic conditions, and the upstream land use. ACTIVITIES The most common maintenance activity is the removal of sediment and organic debris from the system and bypass structures. Visual inspections are routine for system maintenance. This includes looking for standing water, accumulated leaves, holes in the soil media, signs of plant distress, and debris and sediment accumulation in the system. Vegetation coverage is integral to the performance of the system.  A SGW system is a subsurface horizontal filtration system and does not rely on surface soil infiltration capacity for treatment. As such, surface infiltration rates are expected to be low and not a criterion for cleaning. Rather, stormwater access to subsurface treatment is by way of a hydraulic inlet.  It is important to ensure these inlets are performing properly.  ACTIVITY FREQUENCY CLOGGING AND SYSTEM PERFORMANCE Inspect inlets and outlets to ensure good condition and no evidence of deterioration. Check to see if high-flow bypass is functioning.    Remedy: Repair or replace any damaged structural parts, inlets and outlets.  Clear or remove debris or restrictions.  Annually, more frequently in the first year of operation  Check for internal erosion, evidence of short circuiting, and animal burrows.    Remedy: Soil erosion from short-circuiting or animal boroughs should be repaired when they occur.  Check that the system is fully draining within a 24 - 48 hour period after rain events     Remedy: Repair or restore hydraulic inlet or outlet function. VEGETATION Check for robust vegetation coverage throughout the system and dead or dying plants.    Remedy: Vegetation should cover > 75% of the system and should be reseeded and cared for as needed.    Annually or as needed Cut and remove vegetation from the Gravel Wetland System and forebay in order to maintain nitrogen removal performance.    Remedy: The vegetation should be cut and removed from the system to prevent nitrogen from cycling back into the system. Once every 3 years 

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Regular Inspection and Maintenance Guidance for The Subsurface Gravel Wetland Stormwater Management Device

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