307
edits
Changes
沙坝
,no edit summary
====洪水====
Sand dams require careful maintenance, and immediate repair, as flooding causes hundreds of tons of water to fall over the dam wall and onto the spill-over apron. Flood water may also spill over and erode the wing walls and, perhaps, even over the riverbanks during heavy rains. When determining the dam and spillway height at the selected location, it is very important that the water level and flood line remain below the riverbanks after construction of the dam, or that flooding will not lead to problems up or downstream of the dam. If the flood level is higher than the riverbanks, construction of a dam is not advisable.由于洪水会导致数百吨水冲过坝墙，流至溢洪平台，因此沙坝需要精心维护，及时修理。洪水也可能溢出，并侵蚀翼墙，也甚至可能在大雨时溢出河堤。在选址处决定坝高和溢洪道高度时，有两点非常重要：水坝竣工后，水位与洪水高潮线不会越过河堤高度；或是洪水不会导致水坝上下游产生问题。如果洪水位比河堤高，则不建议建坝。
===Construction, operations and maintenance建造、运作与维护===[[Image:Sand dam diagram.JPG|thumb|right|200px|Cross section of a sand dam.一座沙坝的横截面<br> Diagram: Netherlands Water Project. 图片来源：荷兰水利工程。<br>Click image to see details.点击图片查看详情。]][[Image:Sand dam trench.JPG|thumb|right|200px|People excavating a trench. Source: 人们正在挖取沟渠。 来源：[http://www.sswm.info/category/implementation-tools/water-sources/hardware/precipitation-harvesting/sand-dams RAIN (n.y.)]]]
First a trench needs to be dug. Its position is marked out using pegs. Then it is excavated and the soil placed downstream. It can also be dug out into bedrock. It should then be checked for weathering zones and cracks. Round bars are placed vertically along the trench to reinforce it. Then a foundation is laid consisting of 2 layers of cement with barbed wire in between. Once this has set, the trench is filled with masonry or mortar and hardcore. The wing walls and final dam wall can then be constructed. Finally any exposed parts of the construction are plastered.
