Hooghly Estuary Research Articles

Steady State and Time-Varying Water Quality Models for the Hooghly Estuary, India

Steady state and time-varying water quality models for the Hooghly estuary have been developed for the 92.5 km stretch from Tribeni to Mayapur. A hydraulic model of the estuary was previously developed in this connection, based on a simulated channel of trapezoidal cross-section, gradually increasing downstream, and with uniform ground slope. The estuary has also been assumed to be section-ally homogeneous in each of the thirty-seven sections. The advection-diffusion equations have been numerically integrated to compute the instantaneous and time-averaged distribution of BOD and DO. The monthly averages of the quantities over the year have also been determined. The different system parameters have been estimated using available equations and correlations. The calculated BOD and DO values agree reasonably well with the available field data. The study shows that a water quality model based on simulated channel geometry may work well and is useful where a more rigorous hydrodynamic model is difficult to construct and verify.

Growth of Penaeus monodon Fabricius under different environmental conditions

Penaeus monodon Fabricius is widely cultured in India and other Indo-Pacific countries under different environmental conditions. Growth rate of this species, as reported by different authors, varies from 5 mm/month to 47.7 mm/month. Results are described of culture experiments and studies on the growth rate of this species in three impoundments on the Hooghly estuary, India, under different environmental conditions and husbandry practices. The yield ranged between 250.0 and 329.3 kg/ha per 105 days, with growth rates ranging between 39.6 and 41.0 mm/month.

Zweidimensionale nichtlineare Wellenausbreitung in einer Flachwasserflu�m�ndung bei Gezeiten.

A study is made of a two-dimensional mathematical model of nonlinear wave propagation in a shallow tidal estuary using an unconditionally stable numerical scheme. The alternative direction implicit scheme is used to investigate the simulation of the flow pattern of the estuary, and to examine the effects of the changes in the bed topography either due to dredging or due to construction of spurs and guidewalls in tidal flows. The Coriolis force due to rotation of the earth is taken into account in the present two-dimensional model. It is shown that the Coriolis force is responsible for the existence of the transverse component of the flow field. The proposed theoretical model is applied to investigate the flow structure in the Hooghly estuary. The computed results are then compared with the observed values in the Hooghly estuary. A stability analysis of the alternative direction implicit scheme is also included.

A neotype and 2 topotypes for Bola chaptis Hamilton, 1822 (Pisces, Sciaenidae)

Hamilton (1822) described and figured Bola chaptis from the River Ganges, but left no type material. Trewavas & Talwar (1972, p. 11) have described a species that they believe identical with B. chaptis and placed it in the genus Bahaba Herre. Since their specimens came from Burma they did not propose a neotype from among them. During the course of a taxonomic study of the family Sciaenidae, 3 well‐preserved specimens in the collections of the Zoological Survey of India were recognized by us as the same species. They were collected by the junior author at Chinsura in the Hooghly estuary during September 1954. This discovery supports the decision of Trewavas and Talwar to use Hamilton's name and after consultation with Dr Trewavas we have decided to select one of these specimens as neotype of Bahaba chaptis (Hamilton).

Observations on diurnal variations in some selected stretch of the hooghly estuary (India)

As discussed above, the present investigation reveals that: (1) Almost a steady state of dissolved oxygen (6.0 to 6.2 mg/l) was found at Digha water. The highest dissolved oxygen was recorded at Diamond Harbour with the gradual lowering of values at all points from the mouth to the head of the estuary. (2) Average pH at Digha was 8.4, whereas at other centres it was about 8.1. The bicarbonate alkalinity (reserved) of the estuarine water give a good buffering action. (3) The chlorinity conflict at Fuleshwar was maximum and it was minimum at Calcutta. Diamond Harbour occupies an intermediate position in so far as chlorinity conflict is concerned. Digha typified a marine condition. (4) Average air temperature was higher at all stations than the average water temperature. Sudden variations in temperatures were few, an exception in one case was observed when temperature dropped suddenly by 2.5°C at midnight. The overall condition of the estuary during a 24-hour period did not exhibit any adverse condition owing to factors causative to diurnal variations. The public health hazards from the chemical and bacteriological point of view have not been accounted in this study, as such there is a great need to undertake a detailed study on this aspect.

Observation on the probable effects of pollution on the primary productivity of the hooghly and mutlah estuaries

By the use of the light and dark bottles technique, acomparative study of the productivity of the Hooghly and the Mutlah estuaries was made. The Hooghly estuary is a recipient of various pollutants from industries located on its banks, whereas the Mutlah is free from pollutants. The investigation indicated that whereas the productivity in the Mutlah was between 0.562 mg C/m3/day and 0.375 mg C/m3, day, the productivity of the Hooghly was negligible.