13 



county soil surveys. An estimated range of permeabilities for the top 

 30 cm of the soil profile (i.e., defined for this study as the effective 

 root zone) was determined. This range approximated the period required 

 for the root zone to become saturated after inundation. The slowest 

 value in the range of permeabilities was used to determine the minimum 

 duration of inundation required to saturate the soil. A second range of 

 soil permeabilities between the 30-cm and 90-cm depth was determined. 

 The slowest permeability value of the soil profile between 30 and 90 cm 

 was used to estimate the time required for draining of the root zone 

 after dewatering. A mean daily transpiration factor for floodplain 

 forests of 5.6 mm (Brown 1981) also was incorporated for computing 

 desaturation. 



Permeability and transpiration coefficients were provided as pro- 

 gram input, and new flow (or stage) values for hydrologic zone bound- 

 aries were derived that reflected both inundation and soil saturation. 

 This iterative process required a computer search. The computer program 

 added the days of saturation to the days of inundation, and the output 

 was flow (or stage) values that represented the estimated boundary of 

 each hydrologic zone, based on inundation and saturation. The gauge 

 elevation was added to the stage for each zone to obtain the mean sea 

 level elevation at the gauge. When the site was not immediately adja- 

 cent to the gauging station, the change in water surface elevation 

 between the study area and the gauging station was determined using the 

 best available water surface profile data. Appendix B explains how the 

 computer program analyzes the hydrology data to produce zone boundaries. 



