Security and management of small earth dams : A thesis presented in partial fulfillment of the requirements for the degree of Master of Engineering (Natural Resources) at Lincoln University, New Zealand

Abstract

The overall aim of this thesis is to explain the investigations required prior to the design and construction of a small earth farm dam; and to discuss some of the more common failure modes associated with this type of structure. Initially a literature review was carried out to determine what information was available on the preliminary site investigation requirements and design standards and maintenance for small earth dams. A number of dams were then visited and the program for research was based upon the results and conclusions of these visits. The need for a site investigation is explained. A recommended program for investigations prior to the design of earthen farm dams is set out and some of the tests which should be carried out in the course of the investigation are discussed. The environmental, social and cultural impacts of farm dams are discussed. As would be expected with structures of this size the impacts are limited. The system for assigning Hazard Potential Ratings in New Zealand is also covered. The currently recommended procedure for the estimation of peak flood discharges is described. Coupled with this is a brief discussion of the factors which should be considered when selecting the spillway type. Failure modes of farm dams which were encountered during this study are described, as are possible methods for their avoidance. Most of the farm dams visited in the course of this study had "failed" in some way. These failures were normally minor and did not seriously affect either the dams safety or performance. The most common reason for failure was poor construction supervision and/ or method; the most common failure mode was wave lap erosion. The possible implications of the Resource Management Act (1991) on the granting of water rights/resource consents for structures in waterways are assessed.