Streamline pattern and salt leaching through progressive flooding between subsurface drains

Abstract

This paper examines an efficient method of removing salts through progressive flooding of surface strips between subsurface drains. The method has been tested in the laboratory using a sand tank model experiment. The work extends earlier theoretical investigations by Youngs and Leeds-Harrison (2000) which suggest that more uniform leaching with less water can be obtained by constraining the infiltrating area with the use of bunds, initially flooding only the region midway between the drains and then progressively increasing the flooded area towards the drains until the whole area between the drains is flooded.Streamlines were traced to determine flow pattern and solute movement under complete and partial flooding. The tracing results suggest that partial flooding is more effective than complete flooding as the streamlines move faster and require less time to carry the salt towards the drain. The results have been further supported by the pore volumes of solute and salt loads leached under partial and complete flooding. The quarter flooding situation was extremely efficient followed by half and three-quarter situations where solute leaching towards drains was higher than complete flooding. Results show that 59% superfluous good quality water is required to desalinise the area midway between drains with complete flooding, as compared to quarter area of flooding. Similarly, half and three-quarter flooding situations require 21 and 37% additional good quality water, respectively, to leach the same amount of salts from the area midway between drains. RÉ SUMÉCet article examine une méthode efficace pour enlever les sels par une submersion progressive des bandes entre les drains enterrés. La méthode a été testée en laboratoire en utilisant une expérience sur réservoir de sable. Ce travail prolonge les premières recherches théoriques de Youngs et Leeds-Harrison (2000) qui suggèrent qu'un lessivage plus uniforme avec moins d'eau peut être obtenu en contraignant l'infiltration, en submergeant seulement la zone entre les drains puis en étendant progressivement la zone submergée jusqu'aux drains.Des profils ont été tracés pour déterminer le modèle d'écoulement et le mouvement des solutés sous une submersion complète et partielle. Les résultats suggèrent que la submersion partielle est plus efficace que la submersion totale car le profil se déplace plus rapidement et moins de temps est nécessaire pour transporter les solutés jusqu'aux drains. La submersion au ¼ est extrêmement efficace suivie des submersions au ½ et au où les solutés lessivés vers les drains sont supérieurs qu'en situation de submersion totale. Les résultats prouvent qu'un surplus d'eau de bonne qualité de 59% est nécessaire pour désaliniser la zone entre drains par submersion complète IRRIGATION AND DRAINAGE par rapport à une submersion au ¼. De même, les submersions au ½ et au demandent un surplus d'eau de bonne qualité de 21 et de 37% respectivement pour lessiver la même quantité de sels dans la zone entre les drains.

An Analytical Solution for Predicting Transient Seepage into Partially Penetrating Ditch Drains Receiving Water from a Ponded Field

“…This has been observed to be true for both isotropic as well as anisotropic soils and also for both small as well as large times of simulation of a uniformly ponded drainage system. This finding is in concordant with the observations of Kirkham (1965), Youngs (1994), Barua and Tiwari (1995), Youngs and LeedsHarrison (2000), Mirjat andRose (2009), Römkens (2009), Chahar and Vadodaria (2008a, b;, Barua and Alam (2013), and others who also observed that the velocity field at the surface of a ponded ditch drainage system rapidly decreases with the increase in distance from the centre of the ditches. However, from Fig.…”

“…Several studies (Kirkham 1950, 1960, 1965, Dieleman 1973, MartinezBeltran 1978, Rao and Leeds-Harrison 1991, Youngs 1994, Barua and Tiwari 1995, Youngs and Leeds-Harrison 2000, Mirjat and Rose 2009, Römkens 2009, Chahar and Vadodaria 2008a, b, 2012Barua and Alam 2013 -to name only a few) related to ponded subsurface drainage using tiles or ditches clearly demonstrate the fact that the seepage velocity distribution at the surface of a uniformly ponded soil being drained by a network of tiles or ditches is pretty uneven with most of the flow occurring through areas lying close to the vicinity of the drains. Thus, leaching a contaminated soil with a uniform ponding field at the surface of the soil will lead to unequal washing of the soil profile -regions close to the drains will be over-washed and the regions away from the drains under-washed.…”

“…Thus, full ponding of the whole soil for some time followed by ponding of half of the soil profile for more time and then finally ponding quarter of the soil profile in regions located halfway between the drains, may be adopted for having a relatively uniform leaching of a salt affected soil rather than carrying out the leaching of the whole soil all the time -10.1515/acgeo-2015-0069 Downloaded from De Gruyter Online at 09/12/2016 08:51:31AM via free access (Rao and Leeds-Harrison 1991). Another way of addressing the problem is by first ponding fraction of the area midway between the drains and then progressively increasing this area till all the region in between the drains are being covered (Youngs andLeeds-Harrison 2000, Mirjat andRose 2009). Still another way of achieving uniformity of leaching of a salt affected soil is by subjecting it to a progressively increasing ponding distribution from the edge of the drains towards the halfway distance between two adjacent drains -that way, the entire soil profile can be leached in a single stage (Barua and Alam 2013).…”

“…One of the most commonly used methods of controlling salinity in a soil column is to subject the soil to a ponding head of good quality water at the surface of the soil so that the ponding head drives the water though the salt affected soil and in the process washes away a part of the salt present in the soil profile; the salt enriched water is then drained with the help of a network of subsurface drains installed in the soil (Dieleman 1973, Martinez-Beltran 1978, Rao and Leeds-Harrison 1991, Youngs and Leeds-Harrison 2000, Mirjat and Rose 2009, Barua and Alam 2013. Subsurface drainage is also now proving to be of increasing importance for draining paddy fields so as to maintain a favorable soil-water balance at the root zone of paddies (Ogino and Murashima 1993, Tabuchi 2004, Darzi-Naftchali et al 2013) and, most importantly, for providing a check on the emission of methane from these fields, a greenhouse gas the global warming potential of which is measured only next to carbon dioxide by mass (Shiratori et al 2007, Qiu 2009, Zhao et al 2011, Zhang et al 2011-to name a few).…”

Reclamation of Saline Soils by Partial Ponding: Simulations for Different Soils

“…While their theoretical analysis was for coarse‐textured soils, they suggested that the methodology should also be suitable for fine‐textured soils. The partial ponding concept was recently tested by Mirjat et al (2008) and Mirjat and Rose (2009) using laboratory sand tanks. Their results were relatively close to the theoretical predictions by Youngs and Leeds‐Harrison (2000) The experiments by Mirjat and Rose (2009) and Mirjat et al (2008), however, were limited to uniform sand.…”