tailieunhanh - RESTORATION AND MANAGEMENT OF LAKES AND RESERVOIRS - CHAPTER 20 (END)

Nạo vét, do một số thực hành trong quá khứ nghèo, đã nhận được một danh tiếng xấu. Tuy nhiên, đúng tiến hành, loại bỏ trầm tích, hiệu quả, nhưng kỹ thuật quản lý hồ đắt tiền. Chương này là một lịch sử trường hợp mở rộng về loại bỏ trầm tích bị ô nhiễm và thực hiện trước đây có tên là nạo vét "mục đích đặc biệt" đang trở nên phổ biến hơn để hồ phục hồi, ít nhất là ở châu Âu. Chương này mô tả mục tiêu, mối quan tâm về môi trường, độ sâu nạo. | 20 Sediment Removal INTRODUCTION Dredging due to some poor past practices has received a bad reputation. However properly conducted sediment removal is an effective but expensive lake management technique. New to this chapter is an extensive case history concerning contaminated sediment removal and the realization that formerly named special purpose dredges are becoming more common to lake restoration at least in Europe. This chapter describes objectives environmental concerns dredging depths removal techniques lake conditions dredge selection disposal area designs some case histories and costs associated with sediment removal adjusted for inflation to June 2002 . Sediment removal while common is very limited in documentation concerning the success or failure of most projects. Thus material in this chapter is not exhaustive but rather representative of various lake sediment removal procedures. OBJECTIVES OF SEDIMENT REMOVAL Deepening When recreational activities are impaired due to shoaling the only practical means of restoration is lake deepening through sediment removal. According to the United States Department of Agriculture USDA 1971 lakes must have a water volume sufficient to exceed water loss by seepage and evaporation and sufficient depth to prevent complete freezing. In the latter case that means a depth anywhere from to m depending on the region of the country. A depth of at least m is usually required to avoid winterkill of fish in colder parts of the . Toubier and Westmacott 1976 . These and other factors such as intended lake use availability of a suitable dredged material disposal area and available funds must be considered when designing and implementing any lake-deepening project. The reasons for deepening and the means of measuring the success of such a project are the most direct aspects of the sediment removal objectives. Modern dredging equipment efficiently moves large volumes of sediment. Therefore nearly all .