Shoreline Erosion

(Published April 2001)

Shoreline erosion is evident, even in the smallest creeks, anywhere in the County where there are steep banks adjacent to waterways. Trees toppled into the water, or leaning toward it as their roots are bared provide unequivocal evidence of the fact that our shorelines are eroding. If more evidence were needed, one has only to look at the large number of permits which are requested each month by waterfront property owners to control erosion with bulkheads, rip-rap or other means. The sediment eroded from the shoreline is dispersed throughout the creeks and rivers and is one reason why so many oyster beds have been smothered. There are three reasons erosion is rampant.

The first two reasons are coupled. Sea level is rising relative to the land surface. Not only is sea level rising in a absolute sense, but Virginia's Coastal Plain is subsiding (sinking). The two effects are about equal, about 2 millimeters each year, and add up to a net apparent rise in sea level of 4 millimeters each year, or about a foot in a person’s lifetime.

Sea level is rising globally as the result of climatic warming. The evidence that the climate is warming is now overwhelming and is no longer questioned by many scientists. Climatic warming causes sea level to rise by melting continental ice, mostly on Greenland and Antarctica, and by warming the water in the ocean, which then expands. In addition to an overwhelming number of actual temperature measurements, climatic warming is also documented by observations like the retreat of glaciers and ice shelves, and the pole-ward expansion of disease-carrying insects. Still somewhat controversial is the cause of the warming. The majority of scientists have concluded that it is primarily, or at least in large part, caused by anthropogenic "greenhouse gasses". We are adding carbon dioxide (CO2), methane (CH4), chlorofluorocarbons (CFCs) and nitrous oxide (N2O) to the atmosphere, primarily (except for CFCs) as the result of the burning of fossil fuels (oil, natural gas, and coal). Sea level will almost certainly continue to rise until Earth’s fossil fuel supply is exhausted within the next 200 years.

Our land is also subsiding. Earth's crust is in constant motion. Horizontal motion, such as occurs along features like the San Andres Fault system in California, is periodically obvious. Slow vertical movements are usually less violent and harder to document. Briefly, about 10,000 years ago at the glacial maximum, ice extended as far south as northern Pennsylvania and New Jersey. The weight of this ice depressed the land surface beneath it, and bulged up the land near the southern edge of the ice, where we are located. Once the ice melted, the land beneath it rebounded, and the "bulge" began to collapse, manifesting itself in the land subsidence we observe today. There is obviously nothing we can do about this phenomenon, whereas there is something we can do about global warming! A small, but possibly increasing, cause of land subsidence is the steady decline in water levels in wells tapping our deep aquifers. Water withdrawal allows the aquifers to compact, with consequent subsidence of the land surface.

The third reason for shoreline erosion is also our fault. Boat and personal watercraft wakes create waves that undermine the creek banks, especially in the smaller creeks not normally subject to such large waves. The solution is simple: Always Proceed at No Wake Speed in small creeks, and keep your speed down in the rivers, especially if you own a large powerboat. Never make waves larger than Nature makes.

Waterfront property owners bear a special burden in combating erosion as they strive to protect their property. Bulkheads and rip-rap are expensive, effective, and artificial. Alternatives, including "coconut logs" and transplanted grasses, are also being tried, and it remains to be proven how effective they will be if predictions are correct that sea level will rise at least a foot (maybe more!) by the end of the 21st century. If you need help, contact SEAS, and the Shoreline Erosion Advisory Service will be glad to help you at http://www.dcr.virginia.gov/soil-and-water/seas or (804) 443-1494.