| Coastal zone is an important component of nature which contribute magnificentand distinguish resources for man kind. Among the resouces, nature beach getsmore and more attention for it can resolve the offshore wave energy so it is wonderfulnatural coastal protection construction and as well as great travel resources, becomemore popular in China. It is realized that how important the protection of beach andshore is, so the beach nourishment becomes more popular. But nature beach is notso common in our country, instead the mudflat is more common. As a result, weinvented the construction of artificial beach on muddy beach. Weifang resort districtis a great study case of heteropical deposits nourishment in recent years.This paper aims at research the evolution of Weifang artificial beach and itsstability, evaluate this project and summarize successful experience for laternourishment project.The following work has been done:(1) Historical data is collected and classified.(2) Profiles are measured and sediments are sampled during regular field surveys, thebeach evolution is evaluated based on the data acquired before.(3) Factors influencethe erosion of the beach is evaluated.(4) The beach stability is evaluated based onthe results acquired before and its ultimate state is predicted with static cape baytheory, and the half-life of the beach is predicted.(5) The nourishment performanceof the first stage and second stage project is compared, the utility of nourishmentalternatives is evaluated and the successful experience is summarized.The conclusions are as follows:(1) The artificial beach is constructed on the mudflat northwest of the Weifangcoastal ecological tourism resort district, it is heteropical deposits. After November2011the project was done, it suffered severe erosion, only the root of west groin got depositions. The whole east of the beach is almost entirely eroded except the root ofthe east groin. Till May2013, after18months the first stage project was done, theshoreline retreated about108m, the average sectional erosion volume is307.77m3/m,the whole loss of the fill material is about6.6×105m3, grain size of overlying depositsbecome smaller from0.67mm to0.4mm~0.5mm. In September2013the secondstage project is done. Till April2014, the shoreline retreated about7m, the maxsectional erosion volume is32.36m3/m. The erosion is much more relieved.(2) The research area was mudflat, influenced by tide, the sand can be suspendedduring strong tides. At the mean time the most frequent direction and the max wavedirection are both east-west, while the groins open to the NNE direction, which leadthe beach faces the waves directly. Waves make the sand lost and form long-shorecurrent makes sand transfer to the west of the beach. Also this area happens stormsurge a lot, the storm waves reflect at Laizhou Bay head, sea level rises continuously.The wave don’t rub with the seabed in high water level and will directly erode thebeach, transfer the sand along and across beach under the strong along and acrossshore currents.(3) The second stage project turned the beach into artificial cape-bay beach, thecape-bay static theory is applied to evaluate it, simulate its ultimate stability withellipse model. The result shows that the beach is not stable yet, but its form issimilar to the result, and the beach width is not enough. It is because the resource offill material is not so abundant, actual fill volume doesn’t reach the plan. According toDutch’s experience, the half-life of second stage project is calculated and it is7.62a,so the project can be regarded as successful.(4) In first stage project, the groins is almost long as the beach width and leave thebeach faces the waves directly so the groins won’t protect the beach at all. In thesecond stage project, the groins are extended and a new T type groin is built betweenold groins. The active length prolong to400m, the distance between groins cut downto800m, which is two times the active length, confirms to the design principles ofgroins. The east groin head to the NW direction, forms two cape-bay beach with theT type groin in the middle. Waves diffract after pass the headland, so the wave energy minimizes. The second stage project groins work well as beach protection structureand maintain the scenery at the same time. After all, the design is successful andworth generalized.(5) Weifang artificial beach is constructed on mudflat. Upper fill material willmingle with the fine sediment and the layer will be unstable. In the project they usegeotextile and plastic geogrid to separate the mudflat and the upper fill material. Atthe same time they use geotextile tubes filled with sand to protect the beach, whichalso works well. The use of geotextile is new in beach nourishment, and solved thepractical problems, this method will work well for muddy coast distribute a lot inChina. |
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