varying head boundary condition which is in time steps

i want to add a variable head boundary condition in time series as you can see in fig. Western boundary is a varying head boundary condition assign in first order. in rainy season head will get increased. so i want take that in to consideration. i tried 1D linear interpolation and it failed. Data i have is head for 4 locations in western boundary. want it to be changed based time steps. also i want these 4 point heads to be interpolated in each time steps. any help? 

Could you please give more details about the failure? Did you get an error message, are data assigned but in a wrong way? Which settings did you use for the 1D interpolation? Some further hints would be helpful.

i just needed to know how can we interpolated time series IDs which is in different locations?

http://www.feflow.info/html/help71/feflow/mainpage.htm#t=09_Parameters%2F1D_interpolation.html
http://www.feflow.info/html/help71/feflow/mainpage.htm#t=14_References%2FRegionalisation%2F1d_linear.html