1 · What is it?
This patch of woods is a wetland
It sits a little lower than the land around it, between a neighborhood and a road. It's late summer, the ground is dry, and there's no water in sight. So how can it be a wetland?
An interactive guide
Wetlands of Hampton Roads
What they are, what they do for us, and what happens when they're filled in. Pick a type, then click Next to walk through it. Each one takes about three minutes.
In Hampton Roads, most wetlands don't look like swamps. Many are ordinary-looking patches of woods between houses, roads and shopping centers.
1 · What is it?
The water is just below the surface
The cut-away front shows what's underground. The blue band is the water table, the top of the groundwater. Watch a year go by. In winter and spring it rises to the surface and water stands in the low spots for weeks, sometimes months. In summer it sinks out of sight.
1 · What is it?
Three signs make it official
Experts count a spot as a wetland only when it has all three of these:
- Plants that grow in wet ground. Here that's red maple, sweetgum and ferns.
- Soil that has turned grey from being soaked, often with rust-colored spots.
- Water at or near the surface for weeks during the growing season.
Tap the glowing dots on the model to see each sign up close.
2 · What does it do?
It soaks up floodwater like a sponge
Here comes a heavy September storm. The woods soak the rain into their soil and hold the rest in the low spots, then let it go slowly over days instead of hours. The roadside ditch rises, but it stays 1.6 ft below the road.
2 · What does it do?
It cleans the water
Rain washes fertilizer, oil and dirt off yards and roads. While that water sits in the woods, the dirt settles out, and roots and soil bacteria take up the fertilizer or turn it into harmless gas. What drains on to local creeks and the Bay is cleaner.
2 · What does it do?
It's a home for wildlife
Frogs and salamanders lay their eggs in the spring pools, where fish can't reach them. Songbirds, owls, deer and raccoons use the woods all year. In a built-up area, a patch like this may be the only place left for them.
3 · What if it's filled?
Now clear it and fill it in
Suppose the trees are cut down and truckloads of dirt raise the ground a couple of feet so new houses can be built. On a dry day it looks fine.
3 · What if it's filled?
Then the same storm comes
Nothing holds the rain now, so it runs straight off the packed dirt, roofs and pavement. The ditch fills 2 hours sooner and overflows. The road goes under 0.9 ft of water, the shops' parking lot floods, and water pours off the raised lots into the backyards next door. Those homes never flooded before.
3 · What if it's filled?
And it happens every storm, for good
- Every heavy rain from now on floods the road and the neighbors.
- Muddy, polluted water goes straight to the creek and the Bay.
- The frogs, birds and the rest of the wildlife lose their home.
- The ground no longer soaks rain back into the groundwater.
- Fixing the flooding usually takes new pipes and pumps, paid for by the public.
3 · What if it's filled?
That's why there are rules
Filling a wetland doesn't make the water go away. It moves the problem onto the neighbors, the roads and the Bay, and the problem lasts. That's why filling a wetland needs a permit. The rules ask a builder to do three things, in order:
- Avoid the wetland if there's a reasonable way to.
- Keep the damage as small as possible if it can't be avoided.
- Replace what's lost, for example by restoring or protecting wetlands somewhere else.
The goal isn't to stop building. It's to keep one project from flooding everyone around it. Turn Fill it in on and off to compare the two outcomes yourself.
Wetland in placeFilled in
RoadStays openFloods 0.9 ft deep
Neighbors' backyardsStay dryFlood
Water going to the creekSlowed and filteredFast and muddy
Home for wildlifeKeptGone
More detail, for the curious
Mapping codes. Wetlands like this are classed PFO1A (palustrine forested, broad-leaved deciduous, temporarily flooded) or PFO1C (the same, seasonally flooded). On an A site, surface water shows up only briefly after storms, and the soil is mostly dry by late summer. On a C site, shallow water stands for weeks to months in winter and spring, then draws down, and the soil stays saturated for much of the growing season. The model below can show either one.
In this model, the A site holds its water table within a foot of the surface for 57 days in a row in early spring and is about 2.3 ft dry by late summer. The C site has water standing in the low spots about 129 days a year and stays saturated within a foot for about 148 of the 246 days of the growing season.
The three tests come from the U.S. Army Corps of Engineers' 1987 Wetlands Delineation Manual and its regional supplements: hydrophytic vegetation (more than half the dominant plants rated OBL, FACW or FAC), hydric soil, and wetland hydrology (14 or more days in a row of flooding or saturation within 12 inches during the growing season, in most years).
The cleaning step is mainly denitrification. Alternating wet and dry soil lets bacteria turn nitrate into nitrogen gas.
Permits. In Virginia, filling non-tidal wetlands is reviewed by the U.S. Army Corps of Engineers and the Virginia Department of Environmental Quality.
Show the model as:
Along the Bay and its tidal rivers and creeks, the shore is often edged with marsh: low, grassy land that the tide covers and uncovers twice a day.
1 · What is it?
This grassy shoreline is a wetland
Between the woods and the open water is a band of tall grass cut by a small creek. It can look like an empty field of weeds, but it's one of the most important places on the Bay.
1 · What is it?
The tide covers it twice a day
About every 12½ hours the tide rises about 2½ feet. It spreads over the low marsh, then drains back out through the creek. The grasses here are built to live with their roots in salty water.
1 · What is it?
Three signs make it official
It's the same test as any other wetland, and a spot needs all three:
- Plants that grow in wet ground. Here that's smooth cordgrass, saltmeadow cordgrass and black needlerush.
- Soaked, dark soil, thick with roots on top and grey and airless below.
- Regular flooding by the tide.
Tap the glowing dots on the model to see each sign up close.
2 · What does it do?
It's a nursery for the Bay
At high tide, young fish, blue crabs and shrimp swim up into the grass to feed and to hide from bigger fish. NOAA estimates that estuaries like the Bay provide habitat for about two-thirds of the fish and shellfish caught commercially in the U.S.
2 · What does it do?
It feeds and cleans the Bay
Each falling tide carries bits of broken-down marsh grass out to the Bay, food for the small creatures at the bottom of the food chain. The grass and mud also trap dirt and soak up nitrogen from fertilizer and sewage, the pollution that feeds the Bay's algae blooms. The peat stores carbon as well.
2 · What does it do?
It's a storm shield
In a hurricane or nor'easter, the water rises and waves pound the shore. To cross the marsh, the waves have to push through thick grass over shallow ground, and they lose their power before they reach the yard. Meanwhile the roots hold the shoreline in place.
3 · What if it's filled?
Now fill it in
Suppose the marsh is filled with dirt to make waterfront lots, with a wall called a bulkhead along the water. On a calm day it looks like a nice lawn.
3 · What if it's filled?
Then the same storm comes
With no marsh to slow them, the waves hit at full strength. The new houses on the fill flood about 1.9 ft deep, and waves now reach the yard that used to stay dry.
3 · What if it's filled?
And the losses keep adding up
- The nursery is gone, so fewer young fish and crabs survive to be caught.
- More dirt and nitrogen reach open water.
- Waves bounce off the wall and wear away the shore next door.
- The carbon stored in the peat is released.
- The tide is cut off for good. A filled marsh doesn't come back on its own.
3 · What if it's filled?
That's why there are rules
Filling a marsh doesn't stop storms or tides. It moves the damage onto the neighbors, the Bay's fisheries and everyone downstream, and the damage is permanent. That's why work in tidal wetlands needs a permit. The rules ask people to do three things, in order:
- Avoid the marsh if there's a reasonable way to.
- Keep the harm as small as possible if it can't be avoided.
- Replace what's lost.
In Virginia the rules also favor “living shorelines” that keep marsh plants along the water instead of walling them off. Turn Fill it in on and off to compare the two outcomes yourself.
Wetland in placeFilled in
Waterfront homesStay dryNew homes flood 1.9 ft
Young fish and crabsHave a nurseryLose it
ShorelineHeld by rootsErodes next door
Water reaching the BayFilteredDirtier
More detail, for the curious
Kinds of tidal wetland. Near the open Bay these are salt and brackish marshes of smooth cordgrass, saltmeadow cordgrass and black needlerush. Farther up the tidal rivers they give way to tidal freshwater marshes and forested swamps. The marsh surface is a mosaic of vegetated platforms, shallow creeks and mudflats.
The tide in the model uses NOAA's datums for Sewells Point, Norfolk (station 8638610): mean range 2.43 ft, mean high water 2.56 ft and mean higher high water 2.76 ft above mean lower low water. The low marsh sits between mid-tide and mean high water, so it floods on every high tide. The high marsh sits just above it.
The storm is a 3.6 ft surge arriving on a high tide, with waves that lose height across vegetated marsh (an illustrative model). After Hurricane Sandy, Narayan and others (2017) estimated that coastal wetlands in the Northeast avoided about $625 million in direct flood damage.
Permits. In Virginia, work in tidal wetlands is reviewed by the U.S. Army Corps of Engineers, the Virginia Marine Resources Commission and local wetlands boards. Since 2020, state law has favored living shorelines where they're suitable.
Sources
- Environmental Laboratory (1987). Corps of Engineers Wetlands Delineation Manual, Technical Report Y-87-1. U.S. Army Engineer Waterways Experiment Station.
- NOAA Tides and Currents. Datums for 8638610, Sewells Point, VA (1983–2001 epoch).
- U.S. EPA. Wetlands: Protecting Life and Property from Flooding (fact sheet).
- NOAA Fisheries. Estuary Habitat.
- Narayan, S. et al. (2017). The Value of Coastal Wetlands for Flood Damage Reduction in the Northeastern USA. Scientific Reports 7, 9463.
About the models: they're simplified on purpose. Water levels, storm routing and waves come from small illustrative calculations shaped to real behavior and, for the tide, to NOAA's Sewells Point gauge. Heights are stretched so you can see them. Real numbers depend on the site.
Drawing style after Colorfigures by April Zhu (MIT License).