Issue with soil water and tile drainage using different drainage and water table routines

[hydjber]

Dear all,

I tried to implement tile drainage to model runoff in a highly drained lowland catchment with SWAT+. 

But by trying the different teile drainage and water table routines, it gives me rather different results:

tiledrain = 0 and wtable = 0 -> qtile gets pretty small (around 1-5% of total runoff from hru), but soil moisture is twice as high as field capacity

tiledrain = 0 an wtable = 1 -> qtile now is around 80% of total runoff, soil water is as around field capacity but no percolation occurs

when I use a schedule for controlling drainage then soil water doubles and is again much higher than field capacity, even in summer months

tiledrain = 1 -> no tile drainage occurs 

For all cases, surface runoff and lateral runoff are not higher than 10 % each of total runoff in the catchment.

I set drainage parameters as follows:

t_fc = 75 hrs

lag = 16 hrs

drainage coefficient = 30 mm/hr

lat_ksat = 1

and also varied the depth between 0.5 to 2m.

I really have no idea why this high soil moisture and the totally different qtile values occurs by using different wtable routines. For all cases these values seem to be unrealistic. 

Are there probably any parameters that must be set? 

Please help me solving this problem.

Thanks in advance

Jenny

[hydjber]

Dear all,

I attached the tiledrain.str and the soil.sol of my project.

The soil type of the hru's with drainage is sand. Landuse is mostly corn and slope is under 1%.

Best, Jenny