Stormwater Infrastructure Inventory

A stormwater infrastructure inventory was performed to map and assess the stormwater infrastructure in the watershed. The inventory effort is based on Illicit Discharge Detection and Elimination: A Guidance Manual for Program Development and Technical Assessments (Brown et al., 2004). This document provides excellent background information on mapping and understanding municipal separate storm swear systems. The general types of stormwater infrastructures inventoried include dam, culverts, swale and ditch, catch basin and catch basin pipe inlet, discharge pipe and outfall, detention basin, detention basin inflows, detention basin discharge, and detention basin low flow channel.

Discharge Pipe
Discharge Pipe
Roadside Swale
Roadside Swale

Their locations and general attributes are recorded using a Global Positioning System (GPS) in field following the GPS Data Collection Standards by NJDEP (2002). Some exceptions and deviations were made in the interest of expediency or to compensate for difficult GPS environments including heavy tree cover and other obstructed areas. When they occurred deviations are noted in the data set. Most stormwater infrastructure except pipe inlets, catch basins and upstream culverts were photographed as part of the inventory.  The field notes were also taken to record their existing conditions.

Detention Basin
Detention Basin
Detention Basin Outlet Structure
Detention Basin Outlet Structure

Progress and Status

  • The inventory was conducted by the staff at the Hunterdon County Soil Conservation District during 2007 - 2009.
  • The inventory data had been used for developing and locating stormwater BMPs.
  • The final report is completed in June 2010.

Results and Outcomes

The table below presents the inventoried stormwater infrastructure types and their brief description and inventory amounts in the watershed.

Stormwater Infrastructure Type Brief Description Inventory Amount
Catch Basins The primary collection points where stormwater enters into the municipal stormwater system 4482
Catch Basin Pipe Inlets serve the same purpose as catch basins or storm drains, but omit the grate, head and sump found on catch basins 115
Culverts Up Stream A culvert is a conduit used to enclose a concentrated flow. The upstream portion of a culvert signifies the point at where water enters the conduit  714
Culverts Down Stream The downstream portion of a culvert signifies the point at where water exits from the conduit 714
Dams stream structures that hold back, impound, or restrict streamflows 8
Detention Basins Constructed impoundments that may include bermed stream corridors for reducing flooding, lowering the volume and velocity of stormwater flows and/or improving water quality  154
Detention Basin Discharges The point of discharge of a detention basin commonly located in low area adjacent to streams or wetlands 118
Detention Basin Inflows Pipes that carry stormwater into a detention basin 220
Detention Basin Low Flow Channels Defined flow paths located on the floor of a detention basins.  Some basins have multiple channels while others do not have a low flow channel. 196
Detention Basin Outlet Structures A structure that regulates how stormwater flows exiting from a detention basin and ranges from simple concrete weirs regulating flows to complex multi outlet cast concrete towers 151
Discharge Pipes and Outfalls The discharge pipes or pipe outfalls located near streams, wetlands or other low lying areas where stormwater exits the stormwater system 409
Swales and Ditches The defined flow paths that direct stormwater flows and are most common in the more rural area where piped drainage is less prevalent 853

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