While importing the VV band in Sentinel-1 datasets from GEE, there is no problem when I use the following lines:
var collection = ee.ImageCollection('COPERNICUS/S1_GRD')
.filterBounds(dam_basin)
.filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VV'))
.filter(ee.Filter.eq('instrumentMode', 'IW'))
.select('VV');
But replacing the 'VV' with 'HH' leads to the errors in the subsequent lines which worked with 'VV'. The next lines is just thresholding with values less than -14dB.