Science and technology
working with nature- civil and hydraulic engineering to aspects of real world problems in water and at the waterfront - within coastal environments
Coastal Ocean Currents off Rivermouths
. . . the trouble with the world is that the stupid are cocksure and the intelligent are full of doubts. . . This saying from Bertrand Russell (1872 – 1970) is similar to what The Tathagata said in the 152nd verse of the Dhammapada: The man of little learning grows old like a bull. He grows only in bulk, but, his wisdom does not grow. These sayings point one to look deep into things to open one’s wisdom eye, to see the reality of the nature of things – of the existence of uncertainty in the sphere of knowledge (see The Quantum World; Uncertainty and Risk and The World of Numbers and Chances). The necessity of seeing as such – dawns as we continue to learn more – as the horizon of our knowledge continues to expand.
Perhaps – our learning process starts as we begin to develop questions in our mind – like if or when. In computer programming ifs and the answers to such ifs – are used to direct processes in different directions – so does our learning processes. Questions similar like these, reflecting on the past: if I had done things differently . . . if I had been informed differently or were able to see things through my own lens . . . if I had someone powerful on my back . . . so on – and so forth. And intelligent answers to them help us chart future directions. Similarly, such questions can be framed in our mind – at any time – to help examining the pros and cons of making decisions. Sometimes, we fail to ask such questions in time, and mistakes are made – from which recovery becomes difficult. It’s like one of Tagore (1861 – 1941) songs: keno jaminee naa jheta jagelaa naa – saying, why didn’t you wake me up before it was dawn. In one way or another – the consequences of making decisions based on answering ifs –– define the interdependent fluxes in the evolving canvas of life in time, and in the space where one lives – the spacetime.
And as we do so, we begin to realize what Benjamin Franklin (1706 – 1790) once said: . . . without continual growth and progress, such words as improvement, achievement, and success have no meaning . . . Starting from these words of wisdom, let us attempt to understand some dynamics of currents in coastal oceans off rivermouths – focusing on the one, off the mouth of Ganges (Ganga) Brahmaputra River System (GBRS; or the GBM system). Needless to say that such understandings – are very imperative to initiate, manage and execute Civil Engineering on Our Seashore – to achieve sound and sustainable goals. Engineering services are involved in one way or another – in the processes of attaining the 17 interconnected UN declared Sustainable Development Goals (SDG).
Thought of presenting some findings from the 2nd Chapter of my Ph.D. Dissertation – with a note that unlike in An Alluvial River’s Sedimentary Functions, I am keeping the name Brahmaputra River in line with my Dissertation – although its reach in Bangladesh is known as the Jamuna River. Some aspects of this chapter were presented in the Characterizing Wave Asymmetry, with discussions of some theoretical frameworks posted in Nonlinear Waves. This is the only chapter – which I could not manage time to send the manuscript for journal publication. Other chapters are published: Chap 1 (1991), Chap 3 (1995) and Chap 4 (1994). Facilitated by my major Prof WS Moore, the 2nd Chapter benefited from the works and advice of my Dissertation committee member Prof B Kjerfve. Acknowledging them in gratitude – let me move forward to focus on the main contents of this piece – on coastal ocean currents.
In this piece, I am doing this very briefly with some of the interpretations and explanations that accrued from my later experiences and related publications – some of which are summarized and listed in the ABOUT page. Among them, the most relevant publications for this article are: the 1990 IEB Journal Paper on Estuary; the 1991 COPEDEC-PIANC paper; the 1993 Practices and Possibilities; the 1994 Karnafuli River Estuary Hydraulic Behavior; the 1997 Active Delta; the 2001 Suspended Sediment Measurement; the 2002 Geometric Similarity of Deltas; the 2004 Settling Velocity of Natural Sediments; the 2008 Fluid Mud; the 2015 Longshore Transport; and the 2017 Seabed Roughness. It is also enriched by the works done while writing several articles posted in the WIDECANVAS.
Before I begin, a short note on The Coastal Force Fields is helpful. The fields represent a playground of many forcings and responses of different time-scales afforded by different constraints – defined by isobaths and the land-water interface at the shoreline/coastline (see more in the Civil Engineering on our Seashore). Together, the system of forces head to reach dynamic equilibrium (see Natural Equilibrium; Water Modeling).
According to the force fields defined there – GBRS mouth is governed by forces – that are in dominant actions, but differing in the contexts of both space and time - the Metocean Force Field (MOFF), the Extraterrestrial Force Field (ETFF), the Land Drainage Force Field (LDFF) – are all there, together with the Frontal Wave Force Field (FWFF) – which is active in the proximal shoreline and shallow areas. As well important is the Storm Surge that frequents the coastline often. Currents or velocity fields are generated by the development of pressure gradients generated by the highlighted force fields. They are a manifestation of hydrodynamic interactions – of force and response fields – as depicted in the image of Force Fields in a Coastal System.
The Hydro-Geomorphologic Setting – the Processes and Forms.
Let me begin by referring to the attached image (it is enriched by some materials discussed in the Coastal River Delta) – that summarizes some of the key hydro-geomorphologic features and processes of Bangladesh coast. The definitions and delineations have been used by many subsequent authors to describe Bangladesh coastline.
Let me briefly outline the measurements on which the findings described in this article are based (please refer to Chapter 2 of my 1992 Dissertation for details).
Here is a gist on the nature of changing seawater salinity (see Coastal Water to know aspects of it) at measured stations, and the wind-driven circulation (see Storm Surge to know aspects of it).
The set of measurements in waters between 5 and 20 m isobaths – covering nearly the whole stretch of Bangladesh coastal ocean indicate something very interesting about the refraction of tidal wave by deep submarine canyons.
The three sets of described measurements are fairly representative of the river hydrograph and the changing monsoonal wind pattern. In spite of a few exceptions, the data indicate some interesting hydrodynamic characteristics of the surveyed area.
This article is dedicated to celebrate the 51st anniversary of Bijoy Dibash – the Day on 16 December 1971 marks the Liberation of Bangladesh from the tyranny of Pakistani rule. Let freedom loving people from around the world come together to breathe the fresh air of emancipation – by being conscientious, heedful and diligent – whenever – wherever – whatever. And let us do that by remembering Charles Dickens (1812 – 1870), the British writer, novelist and social critic: have a heart that never hardens, and a temper that never tires, and a touch that never hurts.
The Koan of this piece: Be mindful what you think, say or do, because the Sun has the habit of not shining on one place for long
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- by Dr. Dilip K. Barua, 16 December 2022
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