developed a multi-parameter approach to determining MFLs on the freshwater portions of these

rivers that included evaluation of loss of floodplain habitat. This action was concurrent with the

development of approaches by other water management districts in the state. Although

floodplains have long been recognized as seasonally important riverine habitat, floodplain

inundation has historically not been addressed in most minimum flow determinations (Postal and

Richter 2003). Middleton (1999) also points out that regulation of water regimes has not always

fully appreciated the interaction between floodplains and rivers via the flood pulse. Regulation

of river flows can, however, result in decreased stage fluctuations and alteration of inundation

patterns of floodplain wetlands (Poff et al. 1997, Woltemade 1997). Quantification of potential

differences in floodplain inundation associated with differences between minimum flow

requirements and natural hydrologic regimes should, therefore, be a critical component of

regulatory programs that are intended to protect or restore riverine habitat.

 Compared to instream evaluations of minimum flows requirements, there has been

relatively little research on river flows necessary for meeting the requirements of floodplain

species, communities or functions. However, periodic inundation of riparian floodplains by high

flows is closely linked with the overall biological productivity of river ecosystems (Crance 1988,

Junk et al. 1989). Further evidence exists suggesting that floodplain inundation benefits fish

(Ainsle et al. 1999, Hill and Cichra 2002, Wharton et al. 1982), supports high rates of primary

production (Brinson et al. 1981, Conner and Day 1979), is critical to food webs (Gregory et al.

1991, Vannote et al. 1980) and results in development of wetland soils that are important to the

overall function of the river ecosystem (Kuensler 1989, Stanturf and Schoenholtz 1998,

Walbridge and Lockaby 1994, Wharton et al. 1982).