11 



and American elm overstory communities. The herbaceous understory was 

 typically dense with diverse species of trees and shrubs, vines, and 

 herbs. Appendix A includes a general description of each study site. 



Determining Hydrologic Zone Elevations 



Hydrologic data for each site were obtained either from the 

 U.S. Geological Survey (flow data) or from the local Corps of Engineers 

 District (stage or flow data) . Data were analyzed using a FORTRAN com- 

 puter program developed for determining hydrologic zone elevations in 

 study sites where flooding occurred. The program output is the duration 

 of inundation plus soil saturation of each hydrologic zone boundary, 

 expressed as flow rate or stage data. Table 1 presents inundation/ 

 saturation frequency and duration for Zones 2 to 6 . 



Hydrologic zone elevations for each site were computed using the 

 most recent 10 to 20 years of daily stream gauge data. When gauge data 

 were provided as daily discharges (flow rate), a rating table (relation- 

 ship between stage and discharge) was obtained to determine the corre- 

 sponding stages (elevation) . 



Plant species show little or no adverse effects from flooding in 

 the winter (dormant) season (Hall and Smith 1955; Bruckner, Bowersox, 

 and Ward 1973). Therefore, hydrology during the dormant season was not 

 used in this study to determine zones. 



The dates of the first and last day of the growing season for each 

 site were provided as input to the computer program. Growing season for 

 this study was defined as the period between the last average occurrence 

 of 32° F in the spring and the first average occurrence of 32° F in the 

 fall. The program eliminated all nongrowing season data and ranked the 



