93 



3. When inundation ceased, the bucket drained at a rate PKD 

 (inches/hour) . 



4. DEVAPR inches of water were lost daily out the top of the 

 bucket by evapotranspiration. 



5. When the bucket was partially full (i.e., not empty or over- 

 topped by inundation) , a day of saturation was counted. 



Inputs . The following inputs were required for computing days of 

 saturation: 



1. PKD = rate of percolation of water through the soil column. 

 This was estimated from soil conservation service county soil 

 surveys . 



2. PKW = rate at which inundation restores the soil zone to full 

 saturation (inches/hour). (Note: PKW is different from PKD 

 when the underlying soil layer was less porous than the upper 

 soil layer. The soil would wet at the permeability rate of 

 the upper layer, but would drain at the permeability rate of 

 the underlying soil layer) . 



3. CDSZ = critical depth of the saturated zone, which was the 

 depth of wetland plant root zone (10 in.). 



4. DEVAPR = average daily evapotranspiration rate for the site 

 (inches/day) . 



Discussion . This model has no pretense of absolute accuracy; it 

 does not include rainfall, contributions of water from upslope drainage, 

 residual soil moisture held by soil after gravity drainage, and possibly 

 other sources of water. 



Program algorithm, for a "fixed" flow rate . The following 

 describes the program algorithm for a "fixed" flow rate (used at each 

 zone boundary) for computation of days saturated: 



1. For each year, the program started at CDSZ/24*PKW days before 

 the growing season, with an empty "bucket," and used the gen- 

 eral scheme described above to find the depth of water in the 

 root zone at the start of the growing season. A flow rate in 

 the record greater than the "fixed" flow rate filled the 

 "bucket," while a lesser flow rate drained the "bucket." 



2. For each year, the program then checked each growing season 

 flow rate versus the "fixed" flow rate using this starting 

 water depth, and either filled or drained the bucket as 

 appropriate. Each day when the bucket was partially full 

 counts as a day saturated. 



3. Days saturated for each year were added into a single total 

 for that "fixed" flow rate. 



