海堤是沿海地区防御风暴潮的重要设施,但海堤建成之后,堤前海床常遭受侵蚀,威胁海堤安全.本文利用孤东海域近20年水深数据分析了堤前侵蚀过程,探讨海床冲刷机理,并计算极限冲刷深度.结果表明:(1)孤东海堤处于黄河水下三角洲废弃叶瓣侵蚀背景之下,堤前500 m以内海底侵蚀更严重,本文分别称之为背景冲刷和堤脚冲刷,堤前水深由2000年的2～3 m加深到当前6 m左右,堤脚最大水深已超过7 m.(2)背景冲刷主要是由于黄河改道及黄河入海泥沙减少造成的,波浪是其主要动力因素;堤脚冲刷是由于堤前波浪反射、波浪破碎、堤前湍流、沿岸流、离岸流等复杂水动力过程所致.(3)研究区背景冲刷极限深度为7 m,堤脚冲刷极限深度1.7～2.5 m,据此计算堤前极限水深为8.7～9.5 m.
Seabed erosion mechanism and maximum scour depth in front of the Gudong seawall
Seawalls play an important role in preventing coastal areas from storm surges,but the seabed in front of seawalls usually suffers serious erosion after their construction,which would threaten the safety of seawalls.To analysis the scour problem in Gudong Seawall,we recovered the scouring process according to the water depth during the past 20 years,discussed the scour mechanism and cal-culated the maximum scouring depth.The results showed that:(1)Gudong seawall was under the ero-sion background in the abandoned sub-lobes of the underwater delta of the Yellow River Delta,and the seabed within 500 m offshore suffered more severe erosion,which was called background scouring and toe scouring respectively in this manuscript.The background water depth had deepened from 2-3 m in 2000 to the present depth of 6 m,and the maximum water depth at the toe of the seawall had exceeded 7 m.(2)Background scouring was mainly caused by the diversion of the river course and the reduction of sediment into the sea.Waves were the main driving factor for seabed scouring.Seawall toe scouring was caused by complex hydrodynamic processes in front of the Gudong Seawall,such as wave reflec-tions,wave breaking,turbulence,coastal current,offshore current,etc.(3)It was predicted that the maximum scouring depth for background erosion in the Gudong Sea area was 7 m,whilst for toe scou-ring was 1.7-2.5 m,so the maximum water depth in front of the Gudong seawall was 8.7-9.5 m.
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