RAINFALL SIMULATOR GRID LYSIMETER SYSTEM FOR SOLUTE TRANSPORT STUDIESUSING LARGE, INTACT SOIL BLOCKS

A grid lysimeter system and sample collection, containment, and storag e techniques were developed for detailed laboratory studies of water a nd solute movement through intact soil blocks. This was done because e xisting designs and techniques bad important deficiencies and were lim ited in their range of capabilities. Intact 46-cm soil cubes were isol ated, then contained within a polyurethane foam shell, which formed a stable, intimate soil bond, was impermeable to water and strong enough to support a large soil block, while sufficiently elastic to accommod ate soil shrink-swell with changing water content without rupturing. T he soil blocks were instrumented with solution delivery, collection, a nd monitoring systems. A dripper-based simulator delivered steady rain fall ranging from 4.8 to 30.0 mm h-1. The solution collection system w as a 10 by 10 grid of cells (3.8 by 3.8 by 1.3 cm deep) milled into an aluminum block, which individually drained into collection tubes hous ed within a vacuum chamber. The collection grid permitted characteriza tion of spatial and temporal water and solute movement through the blo ck. The solution monitoring system consisted of side-by-side tensiomet er pairs and time domain reflectometry (TDR) probes inserted horizonta lly through the foam shell at four depths in the block. As a partial t est of the system, a bromide (Br-) tracer breakthough curve (saturated flow) was generated at a simulated rainfall rate of 19.2 mm h-1. Flow data indicated that 85% of the water in the block was bypassed by the Br-, and that >99% of the water flow passed through only 26% of the b asal area of the block. The water flow pattern in the solution collect or exhibited no evidence of preferential flow along the interface betw een the soil and the outer polyurethane shell. It was concluded that t he rainfall simulator-grid lysimeter system was operating effectively.