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农外3

(2008-04-16 21:11:15)
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杂谈

 

Lesson 3    Irrigation Methods

New Words & Expressions

  sprinkler  n.sprinkling or device for sprinkling 喷洒,洒水器

  trickle  v. n. to flow in drops or flowing in drops 细流

  subsurface  n.a. below ground 地下(的)

  furrow  n. a trench in the earth made by a plow;  a marked narrow depression 犁沟, 垄沟

siphon  n. a tube that is bent so that a liquid can be drawn upwards and then downwards to a lower level  虹吸管

ditch n. a long narrow passage cut into the earth (as for irrigation);trench 沟渠

  turnout  n.a place where something (as a road) branches off 分叉口

  erosion n. the action or process of eroding 侵蚀,腐蚀

      erode v.

      erodible a.

      erodibility n.

  infiltrate  v. penetrate or permeate 渗入, 渗透

  ridge  n. a narrow raised part of a surface 垄,埂

  overtop  vt.to be higher or better than  超过    ·   

  gully  n. a small narrow valley cut by heavy rain  (雨水冲刷) 溪谷

  contour  n. a line with same altitude  等高线 

        note: attitude, latitude

corrugation  n.wrinkled surface 波纹, 皱纹;small furrow for irrigation 小灌水沟

      corrugate v.

  percolation  n. infiltration or penetration 渗入, 渗透

        percolate v.

  gradient  n. the rate of an ascending or descending slope 坡度,倾斜率

hay  n.dried grass 干(粮,牧)草

topography  n. the character of an area that is related to the shape and height of the land  地形, 地势

  offset  vt. counteract or compensate for  弥补,抵消

  swale  n. lower land 低洼地

  stringent  a. severe or strict严格的, 严厉的

  tile  n. hidden tube 暗管   

  saline  a. salt-containing 含盐的

  sodic  a.sodium-containing 钠质的

  outwash  n.washing out 冲刷,清除

  avocado  n. tropical fruit with a large stone and oily flesh 鳄梨

  bonus   n.advantages优点(好处)

  emitter  n. emitting device 滴头

  encrustation  n.crystallization 结晶, 结壳                                                                        

  clogging  n.blocking or plugging 阻(堵)塞               

 

Text

Irrigation methods can be divided into four main types--surface, subsurface, sprinkler, and trickle irrigation and many subtypes. Surface irrigation is the oldest type and still accounts for about three fourths of all irrigation. Subsurface irrigation is limited in its adaptation. Sprinkler irrigation can be used in any climate, is the most popular method in humid regions, and is still expanding in use. Trickle irrigation, the newest type, makes the most efficient use of water.

灌溉方法可以分为四大类——地面灌溉、地下灌溉、喷灌和滴灌以及许多小类。地面灌溉是最古老的灌溉方式,现在还有大约四分之三的灌溉土地仍然使用这种灌溉方法。地下灌溉的适用性是有限制的。喷灌可以用于任何气候条件,在湿润地区最受欢迎,而且仍在推广使用。滴灌是最新的灌溉方法,使水得到最有效的利用。

1. Surface Irrigation

Surface irrigation includes both furrow and flood types. Furrow irrigation is used with row crops by running water in the cultivated between the rows. The rows can be fed with siphon tubes channel or in groups from ditch turnouts.

1. 地面灌溉

地面灌溉包括沟灌和淹灌。沟灌用于行播作物,水在作物行间的小沟里流动,进行灌溉。灌水沟可通过虹吸管或给沟渠开几个小口进行供水。

Furrow Irrigation Furrow irrigation creates a serious erosion hazard because the water flows in the unprotected area between the rows where the soil has been loosened by cultivation. The maximum non-erosive stream flow in liters per second can be estimated from the equation:

沟灌  沟灌会产生严重的侵蚀危害,因为水在行间耕松了的、未加保护的土壤上流动。以升/秒为单位的最大不侵蚀流速可用下式估算:

                                      0.6 liters/sec

                             Qmax = ------------------------

                                      percent slope

This equation should be used only for slopes of more than 0.3 % because the flow on flatter slopes is usually limited by the furrow capacity rather than by erosion. The 0.6 factor should be decreased if the soil is known to be more erodible than the average.

这个公式只能用于坡度大于0.3%时,因为在坡度较缓的沟渠里,流量通常受到沟渠输水能力的限制,而不是受侵蚀的限制。如果已经知道沟渠土壤比一般土壤更容易遭受侵蚀,那么,式中0.6这个系数应该减小。

Irrigation furrows with slope gradients steeper than 2% are difficult to irrigation without erosion. Large stream would erode the soil and small streams will only flow a short distance before all the water infiltrates.

坡度大于2%时,灌水沟很难避免冲刷侵蚀。流量太大会冲刷土壤;流量太小只能流动很短距离就全部渗入土壤。

Contour furrows overcome this problem because they are placed on a gradient of about 0.5 % across the main slope. Extra care must be taken to be sure that water does not cut through any of the ridges between contour furrows. The resulting overload on the lower furrow could cause it to overtop and begin a chain reaction that would likely produce a gully.

等高沟克服了这个问题,因为这些沟垂直于主坡方向布置,沟道坡度约为0.5%。要格外细心以确保水流不会穿越等高沟间的田埂。在较浅的沟道里,如果流量过大就可能使沟水漫溢,并引起连锁反应,从而产生冲沟。

The length of irrigation furrows is limited by the distance irrigation streams will flow during an irrigation period. Uniform irrigation requires that this period of time be no longer than one fourth of the total irrigation period. For example, the irrigation water should reach the end of the rows in two hours out of an eight hour irrigation period or three hours out of a twelve-hour period. The maximum length of irrigation rows therefore depends on the infiltration rate and erodibility of the soil, the slope, and the amount (depth) of water to be applied. Table 1 contains estimates of the appropriate lengths of rows for various conditions.

灌水沟的长度受到在灌水时间内灌溉水流动距离的限制。均匀灌溉要求灌水时间不长于总灌水时间的四分之一。例如:总灌水时间为8小时,灌溉水流应在2小时内到达尾沟;总灌溉时间为12小时,灌溉水流应在3小时内流到尾沟。所以,灌水沟的最佳长度取决于土壤的渗吸速度和抗冲能力、沟道坡度以及灌水定额(灌水深度)。表1中列出了不同条件下适宜沟长的估计值。

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