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cities or other flood hazard damage-prone areas (see generally papers in Chapter 7, this volume). For example, the Corps of Engineers acquired 8400 acres of wetland along the Charles River north of Boston to reduce future flood losses (Barron, this volume). Flood conveyance. Most riverine wetlands in or along river or stream channels lie within the 100 year "floodway" as defined by the Federal Emergency Management Agency (FEMA) and other flood management agencies. Such natural floodways convey relatively high velocity waters from upstream to downstream points during flooding. FE14A regulations and the regulations adopted by states and local governments in the U.S. prohibit fills or other obstructions in flood- ways which would cumulatively increase flood heights 1 foot (FEMA regulations) or some lesser figure (many state and local regulations). Erosion control. Riverine wetlands help stabilize stream banks and reduce stream meander by reducing the velocity of water flowing through such wetlands and by binding the soil. They also help trap sediment (Greeson et al. 1979; Johnson et al. 1985). Pollution control. Riverine wetlands in and along channels play disproportionately large roles (for their size) in removing sediment, litter, and toxic materials from rivers and streams (Greeson et al. 1979; Mitsch and Gosselink 1986; Hammer, this volume; Ferlow and Ferlow, this volume). They also remove sediment. Because they lie parallel to streams and partially in channels, considerable quantities of pollutants may be removed from water flowing through even narrow bands of such wetlands over many miles. However, some of this sediment and pollutants may be resuspended during floods. Fisheries. Riverine wetlands provide spawning and rearing habitat for pike and a variety of other fish. In addition, floodplain wetlands provide substantial food chain support during both flood and normal river stages (Lambou, this volume; Hall and Lambou, this volume; Thayer et al., this volume; Hesse, this volume). Waterfowl. Riverine wetlands provide critical waterfowl habitat including major "flyways" along the major rivers of the U.S. (Johnson et al. 1985). Other Wildlife. Riverine wetlands and riparian habitat provide critical habitat for a broad range of birds, reptiles, amphibians, and small mammals (see, e.g., Brack, this volume). Recreation and aesthetics. Riverine wetlands along navigable streams provide aesthetic and recreational opportu- nities for canoeing, kayaking, boating, hiking, and other activities (e.g., Smardon, this volume; Palmer, this volume; Pitt and Colton, this volume). River Characteristics Important to Riverine Wetlands Riverine wetland characteristics, functions, and values are highly dependent upon what happens to river flows. River characteristics which influence riverine wetland functions and values include: Water quantity. In general, decreases in river water quantity due to water diversions or extractions for agriculture, commercial, industrial, or domes- tic use decrease the size and functions of downstream wetlands. The quantity of water entering and leaving riverine wetlands directly or indirectly determines water depth and determines flushing rates which, in turn, affect water quality. Water depth. Wetland water depth is determined by the amount of water in a river or stream at various times during a year, the width of the river or stream, and the topography (bottom contours) of the wetland. The bottom contours are, in turn, determined by river erosion and deposition and sediment regimes. Mean water depth determines the type of wetland vegetation (marsh, shrub, forest) and the areal extent of the wetland. Water depth also, to some extent, determines habitat value for fish and other wildlife. Water depth is greatly affected by dams and reservoirs including water release regimes, channelization, and dredging. Water quality. Wetland water quality depends, in large measure, upon the natural quality of the water in the adjacent river or stream and the discharge of nonpoint and point sources of pollutants into the river or stream including sediment, toxics, litter, nutrients, etc. Riverine wetland fishery and habitat may be damaged or destroyed by all types of pollutants. The ability of rivers and river wetlands to assimilate various pollutants and recover from pollution discharges depends, in part, upon vegetation, soils, detention time and natural flushing rates and whether these have been reduced by dams or water diversions. Hydroperiod. The hydroperiod of riverine water entering and leaving a riverine wetland plays an important role in determining its pollution assimilative capacity, its flood storage and conveyance capability, and the vegetation successional 8