Research On Characteristics Of Erosional Hot Spots On Nourished Beach In China

As an effective method for resisting coastal erosion and maintaining balance ofshoreline, beach nourishment, which is also a popular choice for coastal protection inwestern countries, has developed rapidly in recent years in China. The purpose ofbeach nourishment is to hold the nourished sand in the conservation areas stably for along time. However,“Beach Erosional Hot Spots” can destroy the stability ofnourished beach, and shorten the renourishment cycle, what’s more, they will makethe appearance of the entire beach worse.“Erosional Hot Spots” are areas that erodemore rapidly than anticipated or adjacent areas of the nourished beach.This paper selects three typical beach nourishment projects, which areXiangshan-changweijiao beach in Xiamen, Longfengtou beach in Pingtan andBeidaihe west beach. Compared the multi-period shorelines, observational data andremote-sensing images when the three projects were completed, seven erosional hotspots are found in the three nourished beaches, and their scales, locations and shapeare all different. By analyzing the topography and geomorphology conditions, coastalbathymetry conditions, waves conditions and tidal conditions around each erosionalhot spot, the origins and controlling factors of each erosional hot spot are identified.The studies have shown that the occurrence of each erosional hot spot is the result ofmany factors, but there will always be one or two main factors that control theoccurrence and development of each erosional hot spot. The controlling factors ofthese7erosional hot spots found in the three nourished beach are coastal bathymetryconditions, the location of sewage pipes, headlands and the abrupt change of shorelinedirection. Under the control of these four factors, wave energy is redistributed on thenearshore. As a result, high wave energy zones and low wave energy zones have beendifferentiated on the nearshore. When the different wave energy reaches the nourishedbeach, the effects on the different portions of the shoreline are significantly different. Consequently, erosional hot spots appear on the nourished beach.At present, beach nourishment technology research is in the early stage, andmany issues are still in the exploratory stage in China. The design and construction ofon-going projects usually depend on the experiences and lessons of the previousprojects. As a result, there are some resemblances and proximities in the beachnourishment projects. Therefore, the controlling factors in this paper can be used toexplain the origin of other erosional hot spots in some degree, though they can’t makeclear all kinds of erosional hot spots.The governance towards erosional hot spots should follow the principle of“prevention first, combined prevention&treatment and comprehensive treatment”. Inorder to fundamentally reduce or eliminate the impact of erosional hot spots，andreduce the input of human, material and financial resources, all the measures that curethe erosional hot spots should be carried through the whole nourishment process,including preliminary investigations, design phase and construction phase. However,we do not understand the origin and process of erosional hot spots deeply, and can’tpredict accurately the occurrence of erosional hot spots in the design and constructionphase. So we can only take the measures of “combined prevention&treatment andcomprehensive treatment”. In the early stage of erosional hot spots, we can keeperosional hot spots from further deterioration by adjusting and weakening controllingfactors. Such as: set up barrier along the shoreline to weaken wave energy nearshore;fill gaps between the reefs or barriers to weaken the otherness of wave energynearshore; reduce the quantity of sewage pipes to lower their impact on sedimenttransport along shoreline; put some wave absorbers around headland to lower theenergy of reflected wave.