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General guidelines for the design of small homogeneous earthfill dams

TR 1987/24

Report: TR 1987/24
Author: WM Mulholland


This report contains information about what guidelines are in place for building small homogeneous earthfill dams, basically outlining the different requirements in place for dams that do not need to be especially designed.

The report speaks of different foundations of dams, rock, sand and gravel or silt and clay, and the respective design for saturated versus dry foundations.

It then provides an overview of the following things to consider. Firstly, embankment stability, where the slopes must be stable during construction and reservoir operation.  Secondly, crest width, where the minimum is a width that will provide a safe percolation gradient when the reservoir is full. Thirdly, embankment seepage, where the report states that this must be controlled so that internal erosion will not occur. Fourthly, spillway design, where there are a number of standards for how this shall be built, to ensure that the dam will not create erosion. Fifthly, upstream slope protection, where the upstream slope my need to be protected against erosion if it is a large reservoir. Lastly, comments on dam construction and maintenance, where the report extends its useful recommendations given in the above mentioned overview items on how to construct a dam.

The report presents tables with recommended slopes for stabilising fills on saturated silt and clay foundations, and recommended slopes for small homogeneous earthfill dams on stable foundations. It also has a number of figures on design criteria for dams built on different kinds of soils.

**Please note: Recent changes to the Building Act 2004 mean Regional Councils are now responsible for building consent matters regarding dams. Small dams however may be exempt from requiring a building consent and in these circumstances, the "Guidelines for the Construction of Small, Homogenous Earthfill Dams" (referred to in the Regional Plan), may be suitable for dams that do not require special design.

It is the owners responsibility to ensure they are familiar with the legislative requirements regarding their own dams. Further information on the Building Act can be found on the Waikato Regional Council at

General guidelines for the design of small homogeneous earthfill dams
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Table of Contents

Contents I
List of Tables II
List of Figures II
1.0 Introduction 1
2.0 Foundations 1
  2.1 Rock Foundations 1
  2.2 Sand and Gravel Foundations 1
  2.3 Silt and Clay Foundations  
    2.3.1 Design for Saturated Foundations 1
    2.3.2 Relatively Dry Foundations 4
3.0 Embankment Stability 4
4.0 Crest Width 4
5.0 Embankment Seepage 8
6.0 Spillway Design 8
7.0 Upstream Slope Protection 9
8.0 Comments on Dam Construction and Maintenance 0