Margao: A comprehensive district survey report on river sand mining in South Goa district has recently revealed worrying environmental impacts including erosion, degradation and saline intrusion in the Zuari River.
Compiled with data from various government departments and the National Institute of Oceanography (NIO), the report outlines the urgent need for interventions to address cumulative impacts on river and estuarine ecosystems.
“The impacts of sand mining have been detrimental and the sustainability of sand mining is always difficult,” says a quote from the report regarding the impact on the Zuari River.
According to the report, several geomorphological changes have been observed, such as erosion, midchannel/point bar deposition, disappearance of sandbar ripple marks, washing away of old mining pits and signatures of fresh mining pits. Significant river bed erosion was observed in the downstream area, along with other changes such as bar thinning, lag removal, sediment accumulation and exposure/burial of bedrock.
The report said that over the years, several potholes and deep valleys have formed in various parts of the river/estuary. Parts of the lower estuary suffer high salinity, which contributes to the loss of traditional levees protecting adjacent areas.
Factors like land subsidence and removal of sand/sediment from the river bed further increase the damage to the embankment. Salinity intrusion has changed land use, turning paddy fields, coastal areas and mudflats into unproductive or mangrove areas.
The report presents important recommendations, which emphasize implementation of sand extraction guidelines, depth restrictions and an “Environmental Protection and Management Plan”. The plan outlines a team/committee responsible for implementing and monitoring aspects of it, with possible sub-teams and village committees as needed. The report divides the area into four zones based on geomorphology, sensitive areas and numerical modelling.
Zone I, located at the mouth of the jurisdiction of Durbhat village, covers ecologically sensitive areas such as mangroves, urban areas along the river bank and a bridge with potential impacts on the shoreline, geomorphology and bird feeding grounds. The implications require careful consideration. Zone II, between Durbhat to Makasana, includes embankments, mangrove forests and winding areas, due to whose ecological importance it is necessary to avoid winding turns, muddy plains and mangroves.
Zone III, between Makassana and Curchorem, includes serpentine sections and three bridges, requiring restrictions of 500 meters on either side of the bridges. Zone IV shows varying sediment thickness and changes in river bed from Curchorem to the downstream area.
The report also highlights seismic data observations near key areas like Borim Bridge, Ponchwadi-Chandor and Sanvordem-Bagh-Shirphod. These include significant river bed elevation, erosion and post-monsoon changes in sediment thickness, reflecting the dynamic nature of the river environment.
The report outlines that unregulated sand extraction or extraction in sensitive areas, based on baseline data and existing site conditions, will have negative impacts on the environment. To minimize these impacts, the report recommends following minimum areas as per the Sustainable Sand Mining and Management Guidelines (SSMG) 2016 and National Green Tribunal (NGT) directions. Specific areas along river stretches have been demarcated for sand extraction with restrictions. Post-mining scenarios indicate changes in bed level, ranging from -0.2 m to 0.5 m, as observed during monsoon (July – November 2020) and non-monsoon periods (November 2020 – June 2021) Is.
In conclusion, the district survey emphasized the critical need for sustainable sand mining practices to preserve the delicate balance of the Zuari River ecosystem. “Sand extraction is to be done only by traditional (manual) method. No mechanized boat or machinery will be operated. Activity will be limited to available areas only, and the depth of extraction should not exceed 3 meters from the existing baseline profile,” the report said.
