about inflow of seepage and runoff from adjoining plot

[Muhammad Tahir]

I am Dr. Tahir.I am using HYDRUS 2D/3D 2.03.0600 to simulated 2D water dynamics from two different land use at three different hillslope positions ; I have an experimental plot at hillslope (slope °8), divided into 3 sub-plots, i.e. upslope, mid-slope and foot-slope having different soil properties, measured/calculated ETc, runoff and moisture content as time variable boundary conditions of two years trial. I want to measure water balance including moisture contents and seepage from the plots at all three hillslopes, separately. I simulated the water balance, moisture content and seepage at upslope by applying boundary conditions on vertical ”Z” direction as no flux (higher vertical side) and seepage face (at lower vertical side). However, I am confused about the mid slope and foot-slope. If I apply seepage face on both Z sides of mid- and Foot-slope as boundary condition, will it serve the matter? I think no.; How will I add the seepage and runoff (coming from upslope into the mid-slope) as the time variable boundary conditions of mid-slope, and likewise in case of foot slope.
Hoping for early response
HYDRUS team is doing a great job to facilitate the users.
Thanks in advance

[Jirka]

I'm not sure if I understand your problem. Do you have a continuous transect, which has three sections? Can you attempt to simulate that entire domain as a whole. If you define "Meshlines" between different sections, the code will report the flux across this Meshline (between different sections of the domain). At the surface, you can use the atmospheric BC on one section and time-variable flux on the other two section (and request that it is treated as atmospheric BC). The only problem will be the root uptake, since Hydrus handles only one transpiration flux.

If you decide to divide the domain into three parts, then it will indeed be difficult to define BCs to use the outflow from the upper part as inflow in the lower part, since I guess the GW is fluctuating in time. You could perhaps record what its position is, and then use the variable head BC?

J.

[Muhammad Tahir]

Dear Prof. Simunek,
Thanks for so nice reply. Few more questions.......I have a continuous transect (120 m long and 15 m wide, and simulating 1 m soil profile although GW is as low as 50 m, for each land use), which I divided to three sections (each 40 m long). I am using peanut and citrus (citrus almost >80 % covered the surface and don't have data across the tree lines so not using HYDRUS-3D) land use. Measurements of moisture contents were made at 10 m from lower side of each section and runoff at lower end of each section. Soil hydraulic properties of each section are not so different; but only problem I am facing is that soil moisture content increase from upslope toward the foot-slope; so calculated ETc is higher towards lower end; I was not sure to use average ETc across the whole profile; ok I will use this option (as if we divide the domain into three parts it is difficult to define BCs to use the outflow from the upper part as inflow in the lower part). However, if meshlines are used, I get generally the flux (surface runoff/seepage) across these line, but how can I differentiate between runoff and seepage; as I want to calculate the seepage/interflow and runoff separately on this sloppy (8 degree) land. I get the detailed flux e.g. runoff, seepage etc. separately at the lower end of domain only.
Can I simulate the transect as: up-slope (40cm), up- plus mid-slope (80 cm), and up-, mid-, plus foot-slope (120 m). By doing this we can minimize the ETc error at especially up-slope and can get seepage and runoff separately at 40, 80 and 120 m from the top. (sketch of the experiment is attached with)
May be I am wrong in few questions; however wishing the best,
Regards,

[Jirka]

You can have up to 10 meshline across which the code can calculate water fluxes. You can adjust the root distribution function (beta) to have more uptake in the lower part of the domain. J.