Vol. 12, Special Issue 6 (2023)

Author(s):
Sandip Markad, Dhanaji Patil, Adinath Markad and Ajay Nakhawa

Abstract:
Mirya bay (17° 00' 02''N, 73° 16' 50'' E), Ratnagiri, Maharashtra State, situated on the west coast of India, is protected with mountains and rocky ridges on both edges. The bay is characterized by the sandy beach flanked by rocky ridges at northern side and Mirkarwada fishing harbour at the southern side. Mirya beach faced major problem of erosion resulting in loss of beach area to substantial levels and decrease in the width of the beach whereas, Mirkarwada fishing harbor encountered the severe siltation in the basin as well as entrance channel resulting in navigational and mooring difficulties for fishing vessels. Present study was carried out to assess the changes along the Mirya bay for the time period from 1989 to 2009 by using different remote sensing and GIS tools along with field and ground truth data. Digital satellite images of different satellites with different spectral and spatial resolutions were used for the study. The digital satellite images were analyzed by the ERDAS Imagine 9.1 digital image processing software. Digital satellite images were preprocessed to curtail geometric, radiometric as well as atmospheric errors. Different digital image processing techniques were used to map the shoreline for years 1989, 1999, 2004 and 2009 from respective year satellite imageries. Sequential shoreline changes were estimated for time intervals between 1989 to 1999, 1999 to 2004, 2004 to 2009 and 1989 to 2009 by subtraction of respective date binary images derived by different image processing techniques. The Root Mean Square (RMS) error estimates of temporal satellite images used in the present study ranged from 0.1910 to 0.3255 pixels whereas, the average accuracies of 97.5%, 97.2% and 97.3% were achieved for shoreline mapping by histogram thresholding, unsupervised classification of multi-spectral images as well as principal components respectively with good overlapping of mapped shorelines. The Mirya beach was characterized by net loss of 1.83 ha beach area during 1989 to 2009 pertaining to erosion of 4.91 ha and deposition of 3.08 ha beach area. The erosion was dominant at the northern side of the beach, while eroded material was transported towards south and deposited at the entrance as well as at the embayment of the Mirkarwada fishing harbour. The sedimentation in the Mirkarwada harbour resulted in the reduction of accessibility and workability of the harbour. The study showed that there is urgent need to undertake appropriate measures such as formation of small walls or structures to trap the sediment at the northern part of the beach.