You are here


Gathering Information for Wetland Rehabilitation

Sketch the site. To keep track of what youre learning about your potential wetland restoration site, it is helpful to inventory and map its features and ecology. Even if its rough, the map you create will become the framework of your restoration plan. As you sketch, indicate the approximate locations of large special features such as lakes, streams, and nearby rivers. Note the topography of the property, such as whether its flat or hilly, and mark features such as any large hills, ditches, drain tile outlets, springs, potential sources of water; standing water; cropland; and any roads or culverts. Your site inventory can document noticeable changes in the types of plants, and identify mature trees or shrubs. Include animals such as waterfowl or muskrat using the waterways, and any other clues of wildlife use. Take photographs to document the sites pre-restoration condition.

Plan for Sprague River Restoration Plan, Klamath Basin, Oregon

Plan for Sprague River Restoration
Plan, Klamath Basin, Oregon

Gather maps and photos. It is also useful to gather maps and aerial photos documenting current or historic conditions at your site. The map section of the portal will help you obtain information about what wetland soils you have on your site and where they occur; known historic conditions or vegetation communities or assemblages; National Wetland Inventory designations; and topography. This information will assist you in understanding the current condition and restoration potential for your site.

Assess drainage history. To determine if your site is rehabilitatable you need to discover if, when and how your site was drained. Knowing the draining method will be critical in determining how to reestablish hydrologic conditions. The most common hydrologic alterations are ditching, drain tile, diversions and channelization. Many sites have experienced a combination of modifications, such as rows of drain tile running to a ditch. If there are no obvious drainage features on the landscape, you may need some assistance to determine whether the land has been drained.

Assess sedimentation. Eroded soils transported in runoff following rain can completely bury original wetland soils. This sedimentation or siltation is particularly common in floodplains, or down slope from cultivated agricultural fields. Eroded soils are carried to the lowest point in the landscape, generally a wetland. To determine whether sedimentation has occurred on your restoration site, you will need a spade, a posthole digger or soil probe, and strips of lath or wooden wedges to mark the edge of the sediment layer. Dig a series of holes from the interior of the wetland where you think there is no sediment towards the upland slope where you suspect there is sediment. Look, as you dig, for a change in color and texture between the soil layers or profile. The sediment tends to be brown with fine loose particles, horizontally stratified (as if deposited in layers), and has no sands or gravels. The buried wetland soil should be a characteristic black or very dark gray color. Push a wedge or wood strip "shim" into the side of the pit at the boundary between soil layers. Measure and record the depth to the boundary.

Flag your holes so you can locate them again. Dig several lines of pits to determine the depth of sediment across the site. If the sediment is deeper than you are able to reach by hand digging, you can try to determine the depth of wetland soil using a soil probe at the bottom of the pit. Keep careful notes of the position of each pit and the depth of sediment.

To accurately determine the former topography of the wetland before the sediment was deposited, you need to have your site surveyed. The surveyor needs to take two elevations at each soil pit: the elevation of the existing ground surface next to your hole, and the elevation of the original soil, which is where you placed the shim. Using these elevations, you can draw two cross-sections for your site. One will show the existing grade, and the other will show the original grade. The difference between them is an estimate of how much soil needs to be removed if you want to restore the original basin.

Seed Bank Assessment. For thousands of years, wetland plants have produced and dropped seeds into the soil of your wetland. Under the right conditions, seeds buried in wetland soils or under sediment may be viable (living) but dormant, even if the site has been cultivated for decades. Dormant seeds have been known to survive for 80 or more years! These living but dormant seeds comprise what is called the seed bank. By removing sediment overburden or restoring the original hydrology, you can provide the right conditions for dormant seeds to germinate. The more living seeds you have, and the closer the site is to other diverse wetland sites that can serve as a source of new seed, the fewer new seeds or plants you will need to introduce into your project.

To find if you have viable seed in your seed bank, remove plugs of soil from just below the litter layer to test for germination You can take samples to a reliable nursery for help, or do the tests on your own at home. Spread each sample thinly, less than 1/4 inch deep, over sterile potting soil. Allow to grow exposed to light, and water regularly so that the flats are kept moist. You may need some help identifying what seedlings come up. Even if you dont know species names, simply becoming aware that sedges, rushes, and wildflowers (as opposed to reed canary grass) are just waiting to germinate can be of great use as you proceed with your plans.

Authored by Esther Lev, Executive Director, The Wetlands Conservancy (2009)