Redacted for Privacy Abstract Approved: R Steve

AN ABSTRACT OF THE THESIS OF LUIS MURILLO for the MASTER OF SCIENCE (Name) (Degree) in OCEANOGRAPHY presented on McXC\ 3(cLqi (Major) (Date) Title: MODELLING TIDAL CIRCULATION AND DISPERSION IN THE GULF OF NICOYA, COSTA RICA Redacted for privacy Abstract approved: r steve Two numerical models are used to predict tidal circulation and dispersion in the Gulf of Nicoya. The two dimensional Mungall Model is used in. the prediction of tidal heights and velocities. The one dimensional Thomann Model is used to predict tidal dispersion of biological oxygen demand (BOD) and the resultant distribution of dissolved oxygen. Winter salinity data from 1953 is used to compute the tidal diffusion coefficients used by the Thoinann Model. These show great variability. This variability is due to the larger dimensions of the Gulf of Nicoya as compared to other estuaries where the model has been used, to the fact that fresh water convection is unimportant relative to tidal diffusion, and to the distortions implied by using tidal volumes instead of sectional volumes. The mixing effects of wind stress during the summer are evaluated indirectly by the impossi1i1ity of matching the computed salinity profiles with the measured salinity profiles along the longitudinal axis of the gulf during this season. It is found that BOD loads of the order of 1 x pounds/day at any segment are easily carried by the gulf with negligible effects on the resultant dissolved oxygen profile. The mayor six harmonic constituents of the tide at Puntarenas are used to exlte the gulf at its open boundary located between Ballena Bay and Punta }{erradura. Any nonhinearities and phase changes occurring between the entrance and Puntarenas are therefore neglected. These assumptions were necessary due to lack of field data concerning the tides at the entrance. A variable phase difference f or each harmonic con- stituent across the entrance boundary was introduced to model the effect of the orientation of the tidal exitation front. This influences markedly the circulation in the lower southwestern region of the gulfbut is unimportant f or the circulation in the middle and upper northwestern regions where the circulation is mostly one dimensional. The ebb flows occur simultaneously over most of the gulf and are predicted to begin at the second-third hour / of the tidal cycle of 12.2 hrs. The flood flows begin after the ninth-tenth hour. The strongest currents occur on both sides of the San Lucas Island, have magnitudes of 96 cm/sec (1.9 knots) and occur during both the ebb and the flood. The computed velocities obtained using the two dimensional Mungall Model were compared with measured velocities at two locations. Results show partial agreement. Best agreement is found for a Chèzy friction coefficient of 30 m112/sec. MODELLING TIDAL CIRCULATION AND DISPERSION IN THE GULF OF NICOYA, COSTA RICA by Luis Murillo A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Commencement June 1981 APPROVED: Redacted for privacy Profejor ojOceography in charge of major Redacted for privacy Dean of chc of Oceanography Redacted for privacy Dean of Gaduate Sdhool Date thesis is presented Typed by Barbara Hanson for Luis Murillo ACKNOWLEDGMENTS I would like to manifest my gratitude to all those individuals directly or indirectly involved in the pursuit of this investigation. Particularly I would like to thank Dr. Steve Neshyba for his thoughtful guidance during my stay at Oregon State, Dr. Larry Slotta for' his introduction to numerical models, and the Mime Computer Center for providing the funds to use the CYBER 170 facility. I would also like to thank Or'. Victor Neal and Dr. David Griffith for their participation. Finally I would like to thank the University of Costa Rica which provided financial support to carry out my graduate studies at Oregon State University. TABLE OP CONTENTS I. INTRODUCTION ...................................... 1 II. THE GULF OF NICOYA ................................ 8 2.1Physiography of the Gulf of Nicoya ........ 8 2.2Climate ...................................13 2.3Hydrography of the Gulf of Nicoya .........16 2.L.Tides of Central America and the Nicoya Gulf ...............................18 III. THE ONEDIMENSIONAL THOMANN MODEL .................26 3.1Description of the Thomann Model ..........26 3.2Accuracy of the Thomann Model .............30 IV. APPLICATION OF THE THOMAN MODEL TO NICOYA .........35 4.lGeneral Considerations ....................35 .2Implementation of the Thomann Model on the Computer ...........................37 L.3One Dimensional Partition of the Gulf of Nicoya ............................37 4Lj.Tidal Diffusion Coefficients of the Gulf of Nicoya ............................L.l L.5Oxygen Saturation Concentration and Reaeration Coefficients used in the Gulf of Nicoya ............................£4.9 L1..6 Pollutant Distribution ....................52 V. THE TWO DIMENSIONAL MUNGALL MODEL ................. 5.1 Model Description ......................... 5.2 The Finite Difference Formulation of the Equations .......................... 67 5.3 The Numerical Algoritm .................... 68 5J. Stability and Convergence ................. 73 VI. USING THE TWO DIMENSIONAL MODEL IN YAQUINA BAY, OREGON ....................................... 6.1 Procedures ................................ 75 6.2 Results ................................... 78 VII. IMPLEMENTATION OF THE TWO DIMENSIONAL MUNGALL MODEL TO NICOYA .......................... 81 7.1Programming Considerations ................81 7.2General Procedures ........................82 7.3The Two Dimensional Segmentation of the Gulf ...............................82 7.Li. Friction ..................................87 7.5Winds .....................................89 7.6Time Step Considerations ..................89 7.7The Forcing Function on the Lower Boundary..................................91 7.8Number of Tidal Cycles Required for a Steady Oscillatio'i ......................95 7.9Discussion of the Results .................96 7.9.1 Zero phase difference at the entrance boundary .................96 7.9.2 Variable phase differences at the entrance boundary and a Chzv friction coefficient of 30 m'-"/sec .......................110 7.9.3 Conparison with recently published data ....................12'+ VIII. CONCLUSIONS ...................................... 129 8.1 Conclusions on the Use of the Thomann Nodel in Nicoya ........................... 129 8.2 Conclusions on the Use of the Mungall Model in Niooya ........................... 131 BIBLIOGRAPHY ..................................... l34 APPENDICES ....................................... 138 Appendix I. Fortran listing for the modified Thomann Model as used for the Gulf of Nicoya ........................ 138 Appendix II. The two dimensional model: program description .......................169 Appendix III. Fortran listing for the Mungall Model ............................. 176 LIST OF FIGURES Figure Page 1 The Gulf of Nicoya. Geographical location.... 9 2 Isobaths for the Gulf of Nicoya ...............10 3 Five year mean winds at Nicoya ................14 4 Flooding currents in the Gulf of Nicoya as described by the local population ..........19 5 Ebbing currents in the Gulf of Nicoya as described by the local population ..........20 6 Chart of the M cotidal lines .................22 7 Chart of the S2 cotidal lin&s ................. 23 7a Backward difference approximation .............32 8 Sectioning used for the modified onedimensional Thomann Model .....................39 S Dissolved oxygen longitudinal profiles ........56 10 Biological oxygen demand profiles .............58 11 Depths for Yaquina Bay ........................76 12 Measured currents at The Bay and The Bend ...... 78 13 Tidal heights, Yaquina Bay, 5.36 hrs ..........79 l4a Gulf of Nicoya ................................ 8 l4b Grid used for the calculations performed with the Mungall Model ........................85 15 Depths for the Gulf of Nicoya, Costa Rica .....88 16 Isotidal lines in the Gulf of Nicoya 0, t 11.57 hrs .........................97 Figure Page 17 Isotidal lines for the Gulf of Nicoya 0,t3.84hrs .......................... 100 18 Strongest calculatedflooding velocities for Nicoya. = 0,t = 11.32 hrs ............103 19 Strongest calculatedebbing velocities for Nicoya. L4 =0,t 6.0 hrs ..............104 20 Tidal velocities. 0.0 ...................106 21 Tidal currents. 0.0 .....................108 22 Isotidal lines. L .133, t = 11.04 hrs .....111 23 Isotidal lines. & .133, t 4.8 hrs .......113 24 Height difference between the entrance and the head of the Gulf of Nicoya, for a full tidal period ...........................115 25 Strongest flooding currents, .133, t 11.6 hrs ....................... 117 26 Strongest ebbing currents, .133, t 4.8 hrs ........................ 118 27 Tidal velocities at seven locations, .133 ...................................... 120 28 Tidal velocities .............................. 122 29 Calculated and measured velocities at stations 7 and 10 ........................... 127 30 The use of the equivalence statement .......... 171 LIST OF TABLES Table Page I Harmonic components of the tide at Puntarenas.................................... 25 II Partition of the Gulf of Nicoya ............... 42 III Tidal diffusion coefficients used in Nicoya........................................ IV Dependence of the calculated salinity on the fresh water discharge .................. 48 V Hourly

Load more