Erosion Control BMPs Potential Impacts to Snakes
Injury or death to snakes from entanglement in erosion control devices has been documented as a threat to
snakes in some parts of the US. As many City of Phoenix (City) construction projects require the use of erosion
control devices per Arizona Pollutant Discharge Elimination System (AZPDES) permitting requirements, this
report investigates the potential for snake entrapment in erosion control devices in the Phoenix area.
Through literature review it appears that the netting used to contain a matrix material in erosion control
devices is responsible for entanglement, not the matrix material itself. For City projects, netting is primarily
used in erosion control mats/blankets and organic filter barriers such as sediment logs/wattles. The three
characteristics that vary in netting are material used, mesh joint configuration, and mesh opening size. Snake
entanglement hazard appears to be highest for plastic mesh with fixed joints and small mesh openings ≤ 1.0″
x 1.0″ and lowest for natural fiber mesh with loose joints and mesh openings > 1.0″ x 1.0″. However, plastic
mesh with fixed joints and rectangular openings of at least 0.25″ x 1.25″ may reduce entanglement hazard
over fixed mesh openings ≤ 1.0″ x 1.0″. The states of Vermont and Washington, and the province of Ontario,
Canada have cautioned, curtailed or prohibited the use of non-wildlife friendly erosion control materials.
Anecdotal evidence and reports from erosion control industry professionals suggest that the use of wildlife
friendly materials has reduced observations of snake entanglement in Wisconsin.
Wildlife friendly erosion control materials are manufactured and sold by several US companies, but are
currently about double the cost of traditionally used materials. In addition, because wildlife friendly devices
do not appear to be manufactured locally in the Phoenix area, there would be additional freight costs over
non-wildlife friendly products available locally. However, when considering entire project costs, the portion of
the project budget dedicated to erosion control may be so small relative to other budget items that the cost
increase of using wildlife friendly erosion control devices may be negligible over the project as a whole. For
example, the Vermont Department of Transportation calculated the cost increase of natural fiber matting into
the budget of a typical project, and the increase on a $2 million project was approximately $2,500, or 0.125%
of the project budget.
View the rest of the study at this link