Dear All, I’m studying the effect of treated waste water (TWW) used for irrigation, in the soil and the perched aquifer in an irrigated perimeter of 3200 ha situated in northern Tunisia. The water table depth is about 3m, and the soil has a fine texture rich with clay (alluvial). The perimeter is a plain with an elevation not exceeding 11 m and is equipped by a drainage system in default since 10 years ago. I have prepared the database and got the climatic data, irrigation volumes, piezometric measures, salinity in the groundwater, TWW salinity and soil parameters. While analyzing the data I find that the piezometric levels in different observations points have important fluctuations. The same for the measured salt concentration in the perched groundwater. My questions are: - Does the fluctuation of the piezometric levels means that the piezometers are not connected to the perched groundwater or it can be due the heterogeneity of the soil texure? - With a water table depth of 3 m and a loamy clay soil texture, can we have flow fluxes in the soil? (which can be modeled) - To model the salinization process in the perimeter, should we start with an 1D model (hydrus 1D for example) or we can just use a 3D model? Thank you.
A few observations following drought and wildfire in coastal plain of SC USA. Heavy rain on dry soils produced perched water table, dry soil beneath, then below deeper was water table. I have not studied the potential dynamics, just confirming the possible air lock or temporary non-wettable layer or control between water table and heavy surface rainfall or irrigation. How temporary or intermittent perched water tabled are understood and modeled for research or management adjustments, I do not know. But even with a few observations where surface is flooded, perched, and finding dry soil below, suggests a mechanism not well understood, a research opportunity.
Well, according to your explanation, we can say that the equipped drainage system is not in right act(a redistributed Screens net may benefit ) due to various gw level fluctuation and may be associated with high soil heterogeneity or piezometers are not connected to the perched groundwater. in the case of soil heterogeneity , 3D MODEL is the best.
Sincerely
Perched groundwater table is supposed to be at a higher elevation than the regional groundwater table level. However, water level fluctuations can be observed even in the perched aquifer, as the water level fluctuation depends on the input of water by means of rainfall or irrigation water seepage, etc. The height of water level fluctuation may differ from perched and unconfined aquifer, due to variations in the aquifer material (hydraulic properties) and depth below ground surface.
There is not enough information to properly answer the question. The following questions will help provide either further information or stimulate you to collect more data.
1. At what level are the piezometers screened?
2. Are the piezometers sealed above the screen level?
3. Do you have piezometers at different screened depths at each location? This will help decide if there is a perched water table or if it is mounding of the regional water table due to water input at your site.
I sounds as if your drainage system surrounds the experimental area. If so you will find an analytical solution for this which was done by Ed Youngs (Youngs et al. 1989, Hydrological Processes, 3: 301-315). It would be useful to see if given the inputs you could use this to model the groundwater and see what the fluctuations might be.
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