Experimental Study of Formation of Open-framework Gravels

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0304426BridgeAn experimental investigation of the formation of open- framework gravels by midirectional water flows is proposed. Open-framework gravels have very small Imounts of sand and mud in the spaces between the gravel grains, and are significant Jecause of their exceptionally high permeability. They are common in the gravelly river ieposits that form so many important hydrocarbon reservoirs and aquifers. In lydrocarbon reservoirs, open-framework gravels act as "thief zones" during water- Gooding and miscible-gas injection. In many glaciofluvial aquifers, open-framework ~avels allow rapid, localized dispersion of groundwater contaminants. Open-framework ~ravels in rivers are also prime spawning sites for salmonid fish. It is therefore important :0 understand the origin, geometry and spatial distribution of open-framework gravels in )rder to: (1) design oil recovery projects; (2) model contaminant dispersion in aquifers, md; (3) assess the impact of human activities on salmonid spawning. However, the origin n open-framework gravels is poorly understood, and it is difficult to understand and Jredict where they occur in fluvial deposits. Furthermore, the permeability of open- rramework gravel is very difficult to define accurately. The experiments will be used to :est the hypotheses that: (1) open-framework gravels are formed at relatively low ;ediment-transport stage (rather than at high stage) by preferential entrainment and ;eparation of sand and silt, transport of matrix-free gravel as bedload sheets, and ieposition on the lee-side of dunes and unit bars; (2) thick, extensive open-framework ~ravels cannot be formed under steady flow conditions, but require repeated fluctuations in discharge, and; (3) infiltration of sand into open-framework gravel at low flow stage is lot a significant process in forming associated bimodal sandy gravel. The experiments will also allow the permeability of open-framework gravels to be measured much more lccurately than possible up to now, and testing of geophysical techniques that predict ;ediment porosity. The laboratory experiments (which will be videotaped) will be an invaluable learning tool for students. The results will have a major practical impact in the lfeas of hydrogeology, reservoir engineering, and freshwater fish ecology.