Cover Image
close this book Wells construction: hand dug and hand drilled
View the document Acknowledgments
View the document Introduction
close this folder Section one: Planning
close this folder Chapter 1: Introduction to wells planning
View the document A. Overview
View the document B. The need for adequate water supply
View the document C. Involving the local community
View the document D. Selecting the most appropriate water source
View the document E. Site choice
View the document F. Preventing water contamination
View the document G. Types of wells
View the document H. Well sections
View the document I. Materials
View the document J. Tools and equipment
View the document K. Sinking method
View the document L. Preparation for construction
View the document M. Planning
close this folder Section two: Hand dug wells
View the document Chapter 2: Introduction to hand-dug wells
View the document Chapter 3: Well design
View the document Chapter 4: Supplies
View the document Chapter 5: Lowering and raising workers and equipment
View the document Chapter 6: Digging
View the document Chapter 7: The middle section: overview of lining techniques
View the document Chapter 8: Construction of the middle section
View the document Chapter 9: Construction of the bottom section
close this folder Section three: Drilled wells
View the document Chapter 10: Introduction to drilled wells
View the document Chapter 11: Drilling and casing techniques
View the document Chapter 12: Construction: hand rotary and hand percussion methods
View the document Chapter 13: Construction: sludger method
View the document Chapter 14: Construction: driven and jetted
View the document Chapter 15: The bottom section
close this folder Appendices
View the document Appendix I: Conversion factors and tables
View the document Appendix II: Vegetation as an index of ground water
View the document Appendix III: Uses of dynamite in hand dug wells
View the document Appendix IV: Cement
View the document Appendix V: Leveling and plumbing the mold
View the document Appendix VI: Pipe
View the document Appendix VII: Pumps
View the document Appendix VIII: Water treatment in wells
View the document Appendix IX: Rope strength
View the document Glossary
View the document Annotated bibliography

Appendix II: Vegetation as an index of ground water

The presence of certain species of vegetation can be a useful indication that ground water or soil moisture lies relatively close to the land surface. These plant indicators are most obvious in arid parts of the world, where green vegetation stands out, but the principle of using plant species as an index to locate ground water near the surface is equally useful in humid countries. The best relationships are found between certain groups of plants (called plant associations) and the depth of ground water or the salinity of water. In North Africa, for example, research has identified various plant associations (usually three to four main species per association) and their relationship to ground water depth and salt content of the water. The presence of certain trees and shrubs, for example the "salt cedar" type trees (Tamarix species), indicates salty water. Similarly, in the arid western U.S., Tamarix species, cottonwood trees, willows and other plants are associated with shallow ground water tables.

Plants whose roots actually tap the ground water are called "phreatophytes." Due to their high transpiration rates in arid zones, the phreatophytes can "pump out" a small stream or lower the level of a well. This transpiration loss could be of concern if, for example, many trees or other deep-rooted plants are planted around a well for shade or to stabilize sand in a dry, windy setting. High transpiration by the plants also can increase the salt concentration in the well water.

In arid zones, the perennial plants, especially trees and shrubs, are the most useful indicators of ground water. Annual plants, mainly legumes and grasses, are generally not good indicators since they come and go depending on rains and the season of the year.

Generally surveys of vegetation to help find shallow ground water are most effective if carried out in the dry season.

It would be useful at this point to present a table of plant species and plant associations, country by country. Unfortunately this information is not available for most countries, at least not in published form. Even if feasible, a list of all the plant species would be much too large. Finally, most people would need plant pictures and descriptions to accompany the names. You will therefore have to make the effort locally to determine the local plants which are good indicators of ground water, Sources of possible information include experienced well diggers or drillers in the area; water resource engineers; in rare cases, published reports (e.g., old FAO reports); and research station or university botanists. In many cases the necessary information can come only from interviews with these local sources of information.