vena contracta to its opening area. is the ratio of the alternative depths, defined as: For submerged flow, , where , and Logging sluices In the mountains of the United States, sluices transported logs from steep hillsides to downslope sawmill ponds or yarding areas. Nineteenth-century logging was traditionally a winter activity for men who spent summers working on farms. Where there were freezing nights, water might be applied to logging sluices every night so a fresh coating of slippery ice would reduce friction of logs placed in the sluice the following morning. Placer mining applications Sluice boxes are often used in the recovery of black sands, gold, and other minerals from placer deposits during placer mining operations. They may be small-scale, as used in prospecting, or much larger, as in commercial operations, where the material is sometimes screened using a trommel, screening plant or sieve. Traditional sluices have transverse riffles over a carpet or rubber matting, which trap the heavy minerals, gemstones, and other valuable minerals. Since the early 2000s more miners and prospectors are relying on more modern and effective matting systems. The result is a concentrate which requires additional processing. Types of material used for sluice gates Aluminium Most sluices are formed with Aluminium using a press brake to form a U shape Wood Traditionally wood was the material of choice for sluice gates. Cast iron Cast iron has been popular when constructing sluice gates for years. This material is great at keeping the strength needed when dealing with powerful water levels. Stainless steel In most cases, stainless steel is lighter than the older cast iron material. Fibre-reinforced plastic (FRP) In modern times, newer materials such as fibre-reinforced plastic are being used to build sluices. These modern technologies have many of the attributes of the older materials, while introducing advantages such as corrosion resistance and much lighter weights. Regional names for sluice gates In the Somerset Levels, sluice gates are known as clyse or clyce. Most of the inhabitants of Guyana refer to sluices as kokers. Sinhala people in Sri Lanka who had an ancient civilization based on harvested rain water, refer to sluices as Horovuwa. Gallery See also Control lock Floodgate Gatehouse (waterworks) – An (elaborate) structure to house a sluice gate Lock Rhyne Zijlstra – A Dutch name referring to one who lives near a sluice References Further reading External links Soar Valley Sluice Gates Salt/Fresh