Characterisation of the hydraulic properties of soil columns via tension infiltrometer and dye tracer patterns: A dissertation submitted in partial fulfilment of the requirements for the degree of Master of Natural Resources Management and Ecological Engineering

Abstract

Water is a renewable resource, which is naturally recycled in the hydrological cycle. Surface waters have a short residence time in the hydrological cycle, while ground waters have a long residence time. This recycling renews water resources and provides a continuous supply. Nowadays, water management is becoming more and more important, especially the modification of irrigation schemes. An effective irrigation management which is similar to "drainage control" will avoid a high water outflow from an irrigated area and therefore the nutrient losses in the outflow water can be negligible. This is absolutely important because nutrients, for example nitrates and phosphorus, can lead to problems in the drinking water supply of a region with intensive irrigation.Therefore, it is essential to know as much as possible of the soil hydraulic properties and to convert this knowledge into management practices for the efficient use of water and soil resources. Tension infiltrometers have become a valuable tool for field determination of soil hydraulic properties. To estimate necessary input parameters for the Hydros-ID model (which simulates the one-dimensional movement of water and solutes through the unsaturated zone), measurements were obtained in three lysimeters (D, E, F) of: tension infiltration rates, soil water content and suction using time domain reflectometry (TDR) probes and tensiometers, installed at fixed depths. Infiltration experiments were performed under 40 mm and 0 mm suctions. Hydros was used to estimate the soil hydraulic conductivitiy K(h) at the corresponding suction values (h in cm). Water retention data measured on replicate soil cores from the 3 lysimeters and K(h) data were fitted with the Mualem-van Genuchten (MvG) equation to estimate the lysimeters' water retention curves. The resulting curves showed significant differences from the measured ones from the laboratory tension table tests. Further, dye experiments were performed to identify the flow types of the lysimeters. To stain the flow pathways, the lysimeter surfaces were flooded with a dye solution of 10 litres Brilliant Blue FCF with a concentration of 10 g/1. After a few days, the lysimeters were excavated and brought into the lab for the vertical and horizontal profile analysis. Images were taken using a digital camera (Nikon Coolpix 8800) under daylight conditions. Photographs of the soil profiles were processed by image analysis to distinguish between stained and unstained areas and to classify the stained areas into classes of dye concentrations. The flow profiles showed a logical sequence, with macropore flow along cracks for the coarser lysimeters E and F, and homogeneous matrix flow for the finer structured lysimeter D