Taylor &. Francis Intern. J. Environ. Studies, October 2004, Vol. 61(5), pp. 539-549 \3/ IMPACT ON HYDRODYNAMICS OF THE ESTUARINE REGION OF MAHADAYI (MANDOVI) RIVER DUE TO CHANGE IN FLOW PATTERN p. S. KELKAR, A. GUPTA and S. N. KAUL National Environmental Engineering Research Institute, Nehru Marg, Nagpur 440 020, India (Received infinalform July 8. 2004) A proposal to construct a dam on ihe river Mahadayi (Mandovi) for power generafion would change the hydrodynamics of the estuarine stretch of the river. Using DYNH YD, the hydrodynamic model of WASP developed by the USEPA, several space and lime dependent parameters were estimated in the stretch of approximately 80 km from the mouth of the river close to Panaji City up to the village of Sonali, The model was calibrated through the observed and predicted salinity values at various segments for summer and monsoon flows in the tivcr. The channel flow variations in the river and estuarine zone, as well as flow velocities, effect on salinity have been predicted for pre- and post-project scenarios. The natural variation in the river flow during a year was from l.3cLm/s to 824 cum/ s. In the post project scenario, the variation ranged from 18.3cum/s to 724cum/s, respectively. The results indicated that predicted impact of salinity changes in the estuarine portion of the river Mandovi will be marginal. A stretch of about 12.5 km from Usgaon Pali village to Amone village may change from mesohaline to oligohaline during summer due to the construction of the dam. Keywords: Hydrodynamics; Mahadayi river; flow pattern; salinity 1. INTRODUCTION Mahadayi (Mandovi) river, originating from Degaon village in Khanapur taluka in Belgaum district flows through the north Goa district and meets the Arabian sea at Panaji, the capita! of Goa. The river stretch in Goa is about 82 km and depending on the river discharge, the estuarine tidal influence is experienced up to about 30-40 km from the river mouth. A proposal to construct a dam on this river for power generation would change the hydrodynamics of the estuarine zone of the river near Panaji. In keeping with the operation schedule for release of water from the dam, the pre- and post-project flows may change in the river, leading to changes in salinity and associated biota. This paper investigates the changes in saline and fresh water mixing zone in summer and monsoon seasons under pre- and post-project seasons due to corresponding changes in upstream fresh water flow pattern under uniform river hydraulic conditions. *Corresponding author; Dr A. Gupta. Email: esdneeri@rediffmail.com ISSN 0020-7233 print; ISSN 1029-0400 online © 2004 Taylor & Francis Ltd DOI: 10.1080/0020723042000219422