Book SectionsTable of Contents
The Problem Puddle Power Frog-Friendly Backyard Why are we concerned about amphibians?
Wetlands - function/type Wetland issues
How to help amphibians
Community Green Plans
Ecological planning beyond the birdbath Before you start Urban Wetlands Marshes
Drainage ditches Stormwater retention ponds Ephemeral ponds River valleys
Swamps Wet meadows Beaver pond Management
A series of small wetlands along a small stream in the upper reaches of a watershed may require less water and add more acreage to the watershed than a single river mouth wet land. Large bottomland or riverine swamps depend on the regular seasonal flooding for new nutrients imported into the system and for the disturbance flood waters cause. River valleys are important as they provide corridors which link wetlands over great distances and even into our largest cities. Riverine wetlands are connected to nearby watercourses either by river overflow into impervious silt, or clay lined depressions and river scars during flooding or underground through sand and gravel. The inclusion of streamside depressions in which flood waters can be retained well after storm high water events can provide the temporary floodplain wetlands that used to be found in urban areas.
Locating constructed wetlands in lowlands or along river courses maximizes gravity feed, has longer hydroperiod, is less drought susceptible, and minimizes the infiltration of pond water into the groundwater table. Depending on water table or frequency of inundation, permeable or impervious fill material in dikes will regulate infiltration or seepage and hydroperiod. Dikes also provide nesting sites for turtles. Emergency spillways are designed into valley wetlands to provide extra discharge in severe storms so that the wetland structure is not damaged.
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