Stormwater and the Chesapeake Bay

by Eoin Carroll

Last month I told you that the three largest pollutants of the Chesapeake Bay are sediment and excess nutrients (nitrogen and phosphorus).

The majority of these pollutants ended up there via surface transportation caused by stormwater runoff. Stormwater runoff is precipitation (rain or snow) that flows across the land.

Undisturbed land can absorb most precipitation and produce almost no runoff.
It can do this by interception (keeping the precipitation from even reaching the ground), evapotranspiration (releasing water from its leaf pores), and by infiltration (allowing the precipitation to permeate into the ground).

Trees can intercept between 2000 gallons (deciduous) and 4000 gallons (conifers) per year per tree.

Infiltration rates

• Trees                                                                            17 inches/hour
  
• Shrubs and meadows                                             6 inches/hour
• Lawns                                                                           1 inch/hour
• Pavement and other impermeable surfaces    0 inches/hour

For stormwater planning purposes, lawns are categorized as impermeable surfaces due to their low rates of infiltration.

As land is developed, rain that falls on roofs, driveways, sidewalks, patios, and lawns runs off the surface rapidly picking up pollutants as it goes.  This can also cause flooding and stream bank erosion.  It also reduces groundwater recharge.

The old way of dealing with stormwater was to collect, channel, and remove the water as quickly as possible.

The new way is to spread it out, slow it down, and infiltrate as much of it as possible.

If you are a homeowner, you can help reduce stormwater runoff by:

• Reducing the amount of impervious areas (for example, reducing the size of your lawn)
  
• Planting native trees, shrubs, and plants
• Using healthy lawn care practices (most importantly minimizing fertilizer and herbicides)
• Installing rain gardens and rain barrels

Penn State Extension has a great guide called The Homeowner’s Guide to Stormwater which is available on their website and from Extension offices. It has lots of information and ideas to help reduce the amount of stormwater runoff from your property.