A technique to circumvent lower density water trapping by tide-wells

Abstract

A 3-year study of water density differences inside and outside of a conventional tide-well indicated that the average water density within the well is consistently lower than the external ambient waters. The tide-well at Goa is situated at the mouth of the Zuari Estuary, and anomalies were reported at all periods except during peak summer and the onset of the summer monsoon. These anomalies lead to an over-estimation of tide levels by well-based gauges. The month-mean over-estimation in sea level (delta h) is a minimum (2 mm) during the summer monsoon, rises rapidly to over 22 mm after the monsoon, and remains around this peak value for about 3 months before slowly decreasing to about 4 mm by peak summer. The annual over-estimation in the mean sea level (MSL) was 11.3 mm. The limitation of the conventional tide-well could be minimized by arrays of performations on its entire submerged portion, that serve the dual purposes of (1) good mixing between well and external waters, and (2) minimizing the Bernoulli dynamic pressure effects. Density measurements during different seasons indicate that these performations allow free exchange of waters within and outside the tide-well, improving measuring accuracy, but slightly increasing wave effects in the well