Influence of coastal structures on the beaches of southern Karnataka, India

Abstract

Eight beaches of Dakshina Kannada and Udupi districts were regularly surveyed and monitored between 1985 and 1999 to understand morphological changes. During SW monsoon the wide summer beaches of this coast experience erosion. Eroded beaches start growing during post-monsoon period and are fully developed by April/May. These erosional and accretional trends are cyclic and annual in nature. Minimum sediment is stored on the beaches during July/August and maximum during April/May. Sediment budget estimates reveal a net gain and hence, there is an accretional trend along this coast. Wherever erosion becomes severe, construction of seawalls is taken up as a preventive measure. In fact, these structures enhance erosion or shift erosional sites towards adjacent areas or they undergo destruction. Occupation of protected beaches is an added problem. Material from cliff erosion of northern coast and that contributed by rivers of these districts are the major sources of littoral drift and beach sediments. Net littoral drift is towards south and any construction as barrier to this results in erosion on downdrift side. Three case studies conducted at Old Mangalore Port, New Mangalore Port and Kapu-Mulur areas exemplify this trend. Significant morphological changes have taken place at Old Mangalore Port area after the recent construction of breakwaters. The shoreline has prograded by about 225 m on updrift side and retreated by 165 m on downdrift side between December 1993 and July 1995.