PRE­SERV­ING DUR­BAN'S FRAG­ILE GOLDEN MILE

The cur­rent vis­i­ble dam­age to Dur­ban's cen­tral and north­ern beaches is a high pro­file ex­am­ple of what hu­man ac­tiv­ity and cli­mate change can do to KwaZulu-Natal's frag­ile coast­line.

Public Sector Manager - - Message From The Acting Director-general -

Sand min­ing, darn build­ing and har­bour con­struc­tion cou­pled with ris­ing sea lev­els flow­ing from chang­ing weather pat­terns are be­com­ing in­creas­ingly de­struc­tive with costly out­comes. Fur­ther degra­da­tion of Dur­ban's beaches will ob­vi­ously have a neg­a­tive im­pact on the fun lifestyle the city boasts about and - with sun, sea, sand and surf be­ing such as­sets and at­trac­tions • pos­si­bly lead to a down­turn in tourism and eco­nomic de­vel­op­ment. With the above in mind, un­der­stand­ing how to pre­serve or sus­tain­ably man­age our coast­line should be fore­most on the agen­das of plan­ners and de­vel­op­ers. Many fac­tors af­fect shore­line change, in­clud­ing vari­a­tions in sand sup­ply, wave char­ac­ter­is­tics and sea level rises. The shore­line re­sponds dy­nam­i­cally to th­ese fac­tors mak­ing it dif­fi­cult to iso­late one main driver of change. It is there­fore im­por­tant to have a sys­temic un­der­stand­ing of the phys­i­cal pro­cesses that drive shore­line change and what can be done to mit­i­gate the im­pact. Waves are gen­er­ated by the in­ter­ac­tion be­tween wind and the ocean sur­face with ma­jor sea con­di­tion changes typ­i­cally as­so­ci­ated with low pres­sure weather sys­tems that gen­er­ate waves and swells which travel long dis­tances be­fore ar­riv­ing at our beaches. Most of our waves tend to come from a south-east­erly di­rec­tion and a con­se­quence of this is that the waves drive a dom­i­nant along­shore cur­rent from south to north which in turn trans­ports a river of sand in the nearshore zone where the waves are break­ing. Any ob­struc­tion to the flow within this zone will dis­rupt the sed­i­ment move­ment This in­cludes the Dur­ban Port's south­ern break­wa­ter which blocks sed­i­ment mov­ing up the coast re­sult­ing in the build-up of sand at the south­ern side of this break­wa­ter. If this blocked sand is not moved to the area north of the har­bour, the beaches there will slowly erode over the long term. A sand-by­pass­ing scheme is op­er­ated in Dur­ban to pre­vent this from hap­pen­ing, but it re­lies on the avail­abil­ity of dredg­ing ser­vices to im­ple­ment It. While the along­shore cur­rent im­pacts on the shore­line over the long term, large wave events as­so­ci­ated with storms can rapidly erode a beach and cause sig­nif­i­cant dam­age to in­fra­struc­ture in the short term. The sever­ity of this dam­age de­pends on the height of the waves, the di­rec­tion they come from, the du­ra­tion of the storm, and other lo­cal fac­tors. Wave height and du­ra­tion con­trol the mag­ni­tude of the cur­rent, whereas wave di­rec­tions con­trol the move­ment of the cur­rent. Waves that ar­rive per­pen­dic­u­lar to the shore­line do not drive along­shore cur­rents and since waves can come from many di­rec­tions the along­shore cur­rent can re­verse di­rec­tion. Sand eroded from the beach face is de­posited off­shore just be­yond where the waves start break­ing but over time most of this sand is grad­u­ally moved back on­shore dur­ing pe­ri­ods of smaller waves. There­fore, although Dur­ban's beaches ap­pear -un­healthy; given our com­plex coastal en­vi­ron­ment, it is easy to un­der­stand how such con­di­tions have oc­curred. How­ever, the en­cour­ag­ing news is that the beaches will re­cover, with the process tak­ing as long as two years. In­ter­ven­tions to nour­ish the beaches with ad­di­tional sand can speed the re­cov­ery process. Of greater con­cern over the longer term is the global problem of an over­all re­duc­tion in the sup­ply of sand to beaches due to sand-min­ing op­er­a­tions (e.g. for con­struc­tion uses) and the build­ing of darns that trap river sand be­fore it reaches the coasts. About 80% of all beach sand comes from rivers. In ad­di­tion, global sea level rise due to cli­mate change will also have sig­nif­i­cant long term im­pacts on the sta­bil­ity of our beaches. Un­der­stand­ing the dy­namic and sys­temic relationships be­tween di­verse causal fac­tors is a core re­search in­ter­est at the Univer­sity of KwaZulu-Natal's Cen­tre for Re­search in En­vi­ron­men­tal, Coastal & Hy­dro­log­i­cal Engi­neer­ing (CRECHE). CRECHE will con­tinue to ex­plore the prov­ince's vul­ner­a­bil­ity to storms and sea level changes, and de­velop new de­sign so­lu­tions to ad­dress th­ese prob­lems.

The above was writ­ten by Pro­fes­sor Derek Stretch, Dr.Rudi Kim­mie and Dr. Justin Pringle of the Afri­hub and the Cen­tre for Re­search in En­vi­ron­men­tal Coastal & Hy­dro­log­i­cal Engi­neer­ing (CRCHE) in the School of Engi­neer­ing at the Streets (SOS) ini­tia­tive...

Newspapers in English

Newspapers from South Africa

© PressReader. All rights reserved.