Development of Ultra-Sonic Current Meter for Long Term Nearshore Current Observation in Surf Zones and Its Application

1. 冲浪带长期观测用超声波型测流仪的研制：在冲浪带现有超声波测流仪的基础上进行了研制和改进。针对海浪带气泡侵入和波浪破碎产生的流沙等噪声干扰，研制了一种新型的海流计噪声处理电路。由于入射波及其诱发的近岸流，冲浪区的水流是三维的。电流计探头也得到了改进，能够测量电流的三维分量。为检验新研制的海流计的适用性和调查绪形海岸冲浪区的海流，进行了约两年的长期观测。冲浪带的海流特征：利用海流计收集了绪多海岸海流的大量野外资料。对观测数据进行了部分分析，以研究长期近岸水流的特征。1)潮汐的影响不显著，风浪的影响显著。冬季有5次强流，夏季有弱流，但持续时间很短。(2)当季风经过时，在风浪的早期阶段有明显的近海流存在，而在海况充分发育时则有较强的近海流存在，其最大速度可达几十cm/s。这些近岸流的发现可能对解决滩过程有很大的帮助。

1. Decelopment of ultra-sonic-type current meter for long term observation of currents in surf zone: Based on ultra-sonic current meters available in surf zones were developed and improved. for noise disturbance by bubble intrusion and drifting sand by wave breaking in surf zones, a noise disposing circuit of the current meter was newly developed. The currents in the surf zone are three dimensional due to incoming waves and their induced nearshore currents. The current meter probe was also improved being able to measure three dimensional components of the currents. Long term observations of about two years were carried out for examining the applicability of the newly developed current meters and investigating currents in the surf zone at ogata coast.2. Characteristics of the currents in surf zones: A lot of field data of the currents at ogata coast were collected by use of the current meter. The pbserved data were analysed partly to investigate characteristics of long term nearshore currents. 1) No remarkable influence of tides exists and remarkable ones exist due to winds and waves. In winter period, styong currents exist five times a month and in summar period weak currents exist, but their duration are usually very short. 2) When a mosoon passes, at the earier stage of wind waves longshore currents exist remarkablly, but in the fully developed sea state strong offshore currents exist and their maximum velocities reach several tens cm/s. This findings of the nearshore currents may contribute greatly to solve the beach processes.