![]() ![]() Moreover, while structural connectivity is more efficient in the upstream-end soil samples, functional connectivity appeared more efficient in the downstream-end and sediment samples. Results revealed that selective erosion phenomena and sediment transport are responsible for the particle size homogeneity in the sediment samples as compared to the upstream- and downstream-end soils. All the samples were analyzed by traditional soil analyses (i.e., texture, Fourier transform infrared spectroscopy with attenuated total reflectance, C and N elemental contents) and fast-field-cycling (FFC) nuclear magnetic resonance (NMR) relaxometry. Soils sampled at the upstream- and downstream-end of three different length plots were collected together with sediments from the storage tanks at the end of each plot. This paper explores the hydrological connectivity inside the soil (HCS) and its link to sediment delivery processes at the plot scale. The expression “hydrological connectivity inside the soil” has been used here to indicate how spatial patterns inside the soil (i.e., the structural connectivity) interact with physical and chemical processes (i.e., the functional connectivity) in order to determine the subsurface flow (i.e., the water transfer), thereby explaining how sediment transport due to surface runoff (i.e., the soil particle transfer) can be affected. This would simplify the design of subsurface drainage systems and the formulation of subsurface drainage design criteria for different crops and soil types found in the area and possibly throughout South Africa.Connectivity is a general concept used to represent the processes involving a transfer of matter among the elements of an environmental system. Based on these results, it was concluded that DRAINMOD 6.1 can reliably be used as a subsurface drainage design tool in the Pongola region. On the other hand, in clay-loam soil, the same 1.0 to 1.5 m WTD can be achieved when the drain pipes are installed at drain depths ranging from 1.4 to 1.8 m and corresponding drain spacing ranging from 55 to 70 m. Results of simulated WTDs at various combinations of drain depth and spacing indicated that in clay soil a WTD of 1.0 to 1.5 m from the soil surface can be achieved by installing drain pipes at drain spacing ranging from 25 to 40 m and drain depth between 1.4 and 1.8 m. Similarly, simulated and observed DDs during the model validation period also showed very strong agreement, with an R 2 value of 0.801 and an MAE of 0.2 mm Results of the DRAINMOD model evaluation in predicting WTD, during calibration period, showed that there was a very strong agreement between simulated and observed WTDs with a goodness-of-fit (R 2) of 0.826 and a mean absolute error (MAE) of 5.3 cm. ![]() Both WTDs and DDs were monitored from September 2011 to February 2012. Water table depths were monitored in 1.7 m deep piezometers installed midway between two drains by using an electronic dip meter with a beeper, while DDs were measured at drain lateral outlet points, using a bucket and a stop watch. In this study, the performance of the DRAINMOD model (Version 6.1) in predicting WTDs and DDs was investigated for a 32 ha sugarcane field in Pongola, South Africa. Thus, drainage design simulation models provide for a simplistic and cost-effective method of determining the most appropriate subsurface drainage design parameters. The purpose of this research is to show where the dry drainage is effective and to verify its sustainability.ĭetermining optimal subsurface drainage design parameters through monitoring of water table depth (WTD) and drainage discharge (DD) at various combinations of drain depth and spacing is expensive, both in terms of time and money. This general statement, however, is questionable because of the wide range of combination of soil, climate, water quality, surface conditions etc. They indicate that the water table can be maintained at about 1.5 m if cropping is concentrated on 50% of the area. While Gowing and Wyseure (1992) believe that the method is a sustainable and cost-effective solution, Konukcu et al. Water scarcity along with abundance of saline soils in arid and semiarid regions, makes it possible to retire parts of the land to control water table and accumulate salts in the retired parts of the land. ‘‘Dry drainage’’, which is leaving parts of the land retired forever adjacent to the cropped land, has been postulated as an alternative (Konukcu et al. In certain circumstances, the conventional drainage solution may be questionable due to economic and/or environmental limitations. Irrigation without drainage is not sustainable.
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