Analysis of Hydrologic Performance Tests in Unconfined Aquifers
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Analysis of hydrologic performance tests in unconfined aquifers Item Type Thesis-Reproduction (electronic); text Authors Chaudhri, Ata-ur-Rehman,1932- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 02/10/2021 09:31:38 Link to Item http://hdl.handle.net/10150/191469 ANALYSIS OF HYDROLOGIC PERFORMANCE TESTS IN UNCONFINED AQUIFERS by Ata - ur - Rehman Chaudhri A Thesis Submitted to the Facultyof the DEPARTMENT OF HYDROLOGY In Partial Fulfillment of theRequirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 1966 STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of requirements for an advanced degreeat The University of Arizona and is depositedin the University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis areallowable without special permission, provided thataccurate acknowledgment of source is made. Requests for permission for extended quotation from orreproduction of this manuscript in whole or in part maybe granted by the head of the majordepartment or the Dean of the Graduate College when inhis judgment the proposed use of the materialis in the interests ofscholarship. In all other instances, however,permission must be obtained from the author. SIGNED: /i: 4 / APPROVAL BY THESIS DIRECTOR This thesis has been approved onthe date shown below: 2t1-Kk/*' at (I J. G. FERRIS Professor of Hydrology ACKNOWLEDGMENTS The author is greatly indebted to Professor John G. Ferris, thesis director, for his valuable suggestions and guidance in accomplishing this task. Special thanks are due to R. W. Stallman of the Water Resources Division, U. S. Geological Survey, Denver, Colorado, for his letter with valuable suggestions in attacking the solution of unconfined aquifer problems. The author is grateful to Dr. John W. Harshbarger, Chairman of the Hydrology Committee, and to Dr. Eugene S. Simpson for their guidance and encouragement. The author is indebted to Water and Soil Investigation Division of Water and Power Development Authority, and the United States Agency forInternational Development for providing the opportunityand facilities for training the author in hydrology. 311 TABLE OF CONTENTS Page LIST OF TABLES Vi LIST OF ILLUSTRATIONS Vii ABSTRACT INTRODUCTION 1 Location 1 General Features 2 Geology of Indus Plains History of Investigation 6 Initial Pumping Test Program and Preliminary Analysis 7 Previous Studies 8 Nature of the Problem and Purpose of Present Study 8 FLOW REGIME OF A PUMPING WELL 11 General 11 Theis' Model 13 Effects of Anisotropic Conditions l'-I Partial Penetration and Its Effects 15 Non-instantaneous Release Effects 21 Artesian Flow Equations and Their Application to Unconfined System 2i iv V Page AN APPROACH TO PUMPING TEST ANALYSIS 26 General 26 Analysis of BR T/W 9 29 Partial Penetration Analysisof Early Data 31 Probable Magnitude of Anisotropyand Its Effect on Early DataAnalysis 36 Effect of Water TableConditions on Early Data Analysis 39 Delayed Yield Analysis 142 Distance Drawdown Analysis 43 Evaluation of the Magnitude ofPerturbations 46 Results of Selected Tests 51 Behaviour of Shallow ObservationWells 53 AUXILIARY TECHNIQUES 58 Time Drawdown Semi-log Plots 58 Estimation of Probable Errorin Specific Yield 63 Specific Yield CalculationOflBasis of Volume of Cone ofDepression 65 70 CONCLUSIONS 73 APPENDIX A DETAILED DATA OF TEST WELL 83 APPENDIX B GLOSSARY OF SYMBOLS 87 REFERENCES LIST OF TABLES Table Page Vertical Head Difference Between Deep and Shallow Wells at 21000 Minutes 30 Results of Early Pumping Test Data After Hantush (1961) 35 Partial Penetration Correction for Observation Wells 145 52 -i. Results of Selected Tests Initial Storage Coefficient asDetermined from Deep and Shallow Wells 57 Drawdown of Deep and Shallow Wells After First 10 Minutes 57 Slope Per Log Cycle ofTime-Drawdown Graphs at Later Times 62 vi LIST OF ILLUSTRATIONS Figure Page Location Map of West Pakistan 3 Sub Surface Formations of Rechna Doab 5 Potential Distribution Around a Non-penetrating Well 16 Ii. Potential Distribution Around a Well Penetrating Upper Half of 125 Feet Thick Sand 16 Transition from Initial Artesian Response to Water Table Response Due to Delayed Yield 23 Type Curves for Selected Observation Wells Taking into Account Partial Penetration Effects for Analysis of Early Pumping Test Data 33 Plots of Early Pumping Test Data of Selected Observation Wells 34 Type Curves Taking into Account the Partial Penetration and AnisotropiC Effects for a Deep Well 50 Feet from BR-T/W 9 38 Type Curves Indicating theDifference if the Effect of Vertical Componentof Flow due to Lowering WaterTable is Neglected 41 Partial Penetration Correction Incorporated in Distance-Drawdown Plot (BR-T/W 9) 147 vii viii Figure Page Observed and Estimated Drawdown for the Deep Observation Well 50 Feet from the Pumped Well 48 Magnitude of Departures from Theis'Initial Artesian Model with Time for Variou Conditions for the Deep Well 50Feet from BR-T/W 9 50 Time Drawdown Plot of Deep andShallow Observation Wells at 100 Feetfrom BR-T/W 8 60 Time Drawdown Plot of 300,500 and 1000 Feet Observation Wells(BR-T/W 8) for Estimation of "ds/dt." 15, Plot of CumulativePumping and the Volume of the Cone of Depressionfor Estimation of Specific Yield 69 ABSTRACT Evaluation of aquifer characteristics was one of the facets of hydrologicalinvestigations started in Rechna and l95 in the Indus plains of WestPakistan. Chaj Doabs (area between Ravi andChenab rivers; Fig. 1) were the first to beinvestigated. Analysis of the pumping tests in these areas wasmade after methods of Theis and Jacob. The values of storagecoefficients obtained indicated artesianconditions but this was in conflict with the availablegeological evidence. TransmissibilitieS were alsoquestionably high, and there was a disparity betweenresults calculated from time-th'awdown versusdistance-dX'aWdoWfl analyses. The purpose of thepresent study was to under- stand the flow regimearound a pumping wellin the area inapplicability of of study; to identifythe causes of Theis' analysis method,and to evaluatealternative approaches for analysisof pumping tests inthis area. Analysis of fourspecially designed long components duration pumping testsindicates that vertical variable of flow due topartial penetration and a the two storage coefficientdue to slow drainage are ix x major factors which control the aquifer response and make Theis' method inapplicable. In the initial pumping period the effect of partial penetration on drawdownis very significant whereas the effectof delayed yield is inappreciable. In general, the effect of partial penetration is more pronounced throughout thepumping period as compared to delayed yield. However, with increasing distance from the pumping well, thepartial penetration effects decrease rapidly andthereby become less important. It was found that analysis of thefirst 20 - '#0 minutes of pumping data, with allowancefor partial penetration, gave an accurate valueof "P" and artesian storage. In most cases the effectivedepth of aquifer could also be estimated. Observation wells at about l.5b or farther from thepumped well, with adjustment for delayed yield, gave goodvalues of specific yield and transmissibility. Close agreement was observed between the values of"T" from both methods. The use of data of nearer wells for thepartial penetration analysis, and the farther well data atlater times for the delayed yield analysisprovided the best approach for aquifer characteristicdetermination. xi In the present analysis the effects of anisotropy and vertical component of flow due to lowering water table are so small relative to the partialpenetration influence that they do not affect the early dataanalysis. However, a method has been suggested to accountfor these factors if in any test their magnitude appears significant. The average value found forpermeability was 7.5 x 1O ft/sec, the artesian storage coefficient was in the range of 0.0001 - 0.005, andspecific yield was 0.2 - 0.25. The effective depth of aquifertaking part ranged from 720 feet to over 1500feet. INTRODUCTION BanDoab (doab means the land between two rivers) and the Bhawalpur area, where these tests were conducted, form a small part of the IndusPlains, West Pakistan. In order to identify the hydrologicenviron- ment, a brief description of WestPakistan seems appropriate. Location The State of Pakistan emerged on theworld map as an independentsovereign state on August lii-,l9L.7, as a result of thepartition of the subcontinent ofIndia. It has two parts, namely, WestPakistan and East Pakistan, separated by 1,000 milesof Indian territory. (Fig. 1) West Pakistan occupies thewesterly portion of the Indo-Pakistansubcontinent between longitudes 61 to 75 degrees east, andlatitudes 2 to 37 degrees north. On the west it is boundedby Iran, on the north and northwest by Afghanistan,Oflthe northeast by Azad- Kashmir and the disputedterritory of Jammu andKashmir, 1 2 and on the south by the Arabian Sea. Its area is 310,'403 square miles and according to the 1961 census, its population is '42,968,000. General Features West Pakistan on its north touchesthe Himalayan foothills and the Hindukush mountains. The rugged mountainous region gives way to theplains and fertile land of the Indus valley and thenceto barren deserts in the south and west. The Indus plains constitutethe central portion of the Indus valleyand have an area of about 50 million acres. West Pakistan has three welldefined seasons: winter, summer, and monsoon orrainy season. In some parts the winter is extremelycold but generally dry. The summer begins inmid-April, and during the nextthree months the temperature in theplains may reach 120° F. Between July and Septemberthe monsoon provides an average rainfallof about 10 inches in theplains to about 60 inches in thehills. Figuxe 1 Location map of Pakistan. K II 8064° 120 ITS68° SR /72°S S I.