A simulation study of erosion in the Emerald Irrigation Area

Sedimentation in the drainage network of the Emerald Irrigation Area (near Emerald, Queensland), as a result of erosion from irrigated farms, is a ser ious problem. Deposited sediment changes the hydraulic characteristics of t he drains causing flooding and is difficult and expensive to remove. We use d the GLEAMS erosion model to simulate a range of management strategies aim ed at reducing sedimentation in the drains by reducing erosion at the bay/f ield scale or retaining eroded sediment on-farm. GLEAMS was set up and tested using data measured at the rainfall simulator (12 m(2)), furrow (0.2-0.3 ha), and bay (20-30 ha) scales. Comparisons of m easured with predicted sediment transport indicated the model accurately re produced erects of several management treatments on sediment transport and the size distribution of eroded sediment at the bay scale. To reproduce acc urately size distribution of eroded sediment, though, an important paramete r, clay content of surface soil, had to be substantially distorted from mea sured values. GLEAMS was used to simulate sediment transport from a typical farm producing irrigated cotton. Management strategies simulated included conventional (bare), stubble retained, cover in the tail-drain, drip irriga tion, and addition of a silt-trap and storage. The most effective management strategies for reducing erosion and sediment transport at the bay scale were stubble retained and drip irrigation. Stubb le retained+drip irrigation almost eliminated sediment transport. Addition of a silt-trap and storage with conventional management reduced sediment tr ansport or-farm by 45%. Use of a silt-trap with improved field management f urther reduced sediment transport. Erosion and sediment transport at the ba y scale was sensitive to changes in the furrow/tail-drain layout. Changes i n the furrow/tail-drain layout from the original design should be undertake n carefully so as not to increase sediment transport off-farm.