Grey Infrastructure – Culverts
Map of number of stream crossings per HUC-14 in the Raritan Basin
Culverts, constructed of concrete, brick/clay, iron, corrugated steel and corrugated aluminum, are commonly used to enable stream crossings for roadways. If not properly positioned, sized and maintained, they can impede fish passage, restrict stream flows, increase stream velocity, become clogged with debris and sediment, increase the likelihood of contaminated road runoff entering waterways, and generally disrupt the connectivity of rivers and streams. Of particular concern are culverts that are too small to carry peak flows and those that are located above the natural stream bed (perched) in fish-bearing streams. The former can cause flooding and bank erosion while the latter can scour stream beds; both may impede fish passage.
The NJDOT maintains a database of state-owned culverts with openings greater than five feet and less than 20 feet (openings greater than 20 feet are categorized as bridges) and inspects them on a four-year cycle. While there is no state or federal requirement for statewide inspection of county or municipal culverts, in 2007, the NJDOT announced it would fund local inspections and would develop a culvert inventory system that included municipal and county culverts (NJDOT 2007).
Nearly 70% of the 5,247 culverts/stream crossings in Raritan are on first- and second-order headwater streams. If not well maintained they can imped fish passage, alter flows, and negatively impact water quality. There is no requirement for inspection of smaller state-, county-, or municipal-owned culverts.