The Role of Kelvin Number on Bulge Formation from Estuarine Buoyant Outflows

Abstract

This investigation examines the influence of the Kelvin number (K) and fractional depth (h/D) on bulge formation from buoyant outflows from an estuary or strait perpendicular to the coastline. Here K = W/R is the ratio of the width (W) at the mouth of the estuary to the deformation radius (R), and h and D are the buoyant layer and ambient ocean depths, respectively. Measurements of velocity and lateral shear (≈ relative vorticity ζ) at the baymouth are reported for experiments on a flat-bottomed rotating turntable. The form of the velocity profile across the mouth depends on the value of K. The buoyant outflow flows across the entire width of the estuary for narrow estuaries (i.e., K ≤ 1). In contrast, for wide estuaries (K > 2), dense oceanic water inflows on the left and the buoyant waters outflow on the right (looking seaward). Velocity profiles of the inflowing oceanic waters are laterally uniform with velocities (V/C ≈ −0.4), whereas velocity profiles of the outflowing buoyant waters are laterally sheared with peak velocities of V/C ≈ 1.0 at the right hand exit. The flow pathways when bulges form comprises an anticyclonic turn offshore of the mouth and a downshelf propagating coastal current. Anticyclonic bulges form for surface-advected outflows h/D < 0.25. Anticyclonic bulges do not form for sufficiently large magnitudes of non-dimensional relative vorticity ζ/f (>0.4), and an additional flow pathway is that buoyant waters recirculate back cyclonically into the estuary at the left-hand (upshelf) side of the estuary. The offshore extent of buoyant waters associated with this cyclonic recirculation can be as large as 7R.

Appendix

Q O	T	g0′	W	D	C	R	h/D	K
cm3/s	s	cm s−2	cm	cm	cm/s	cm	–	–
10	13.1	14.7	15	8	4.1	4.3	0.14	3.5
10	10.1	4.9	3.6	8	3.3	2.7	0.28	1.3
10	10.1	4.9	10	8	3.3	2.7	0.28	3.8
10	10.1	4.9	12	8	3.3	2.7	0.28	4.5
10	10.1	4.9	15	8	3.3	2.7	0.28	5.6
10	10.2	4.9	15	2	3.3	2.7	1	5.6
10	14	14.7	15	2	4	4.5	0.55	3.3
10	14	14.7	3.6	2	4	4.5	0.55	0.8
10	14	14.7	10.5	2	4	4.5	0.55	2.3
10	14	14.7	12.2	2	4	4.5	0.55	2.7
10	14	14.7	10.5	4	4	4.5	0.28	2.3
10	14	14.7	15	4	4	4.5	0.28	3.3
10	10.1	4.9	15	4	3.3	2.7	0.56	5.6
10	14	14.7	10.5	6	4	4.5	0.18	2.3
10	14	14.7	12.2	6	4	4.5	0.18	2.7
10	14	14.7	12.2	4	4	4.5	0.28	2.7
10	10	4.9	15	6	3.3	2.7	0.38	5.7
10	16.2	14.7	5	1	3.9	5	1	1
10	16.2	14.7	5	2	3.9	5	0.5	1
6.7	13.4	4.9	6	2	2.8	3	0.8	2
6.7	12	14.7	12	4	4.2	4	0.3	3
6.7	11.8	4.9	12	2	3.2	3	1	4
10	10.1	4.9	15	6	3.3	2.7	0.38	5.6