Earth dams, a study — Key Ideas to Explore

From Yarrow to Tabeaud: The Role of the Case Study

The book’s structure alternates between theoretical chapters and extended case studies. Chapter II introduces the Yarrow Dam site with a longitudinal section and cross-section (Figs. 1, 2), showing how Bassell uses a single location to illustrate preliminary investigations. But the centerpiece is Chapter IV, devoted entirely to the Tabeaud Dam. Here the reader finds a plan of the reservoir, details of bed-rock drains, and a view of the completed embankment (Figs. 3–13). Bassell does not merely describe; he walks through the construction sequence, from trenching to drain placement to the final “dimension section.” The Tabeaud example serves as a concrete anchor for the principles of drainage and saturation control that recur throughout the text.

Saturation Lines and the Croton Valley Evidence

A recurring image in the study is the “plane of saturation” within an embankment. Bassell reproduces cross-sections of two Croton Valley dams—Bog Brook and Middle Branch—showing the saturation line rising through the outer bank (Fig. 18). He then presents the findings of a board of experts who determined that “the slope of saturation in the best embankments made of the material found in the Croton Valley is about 35 ft. per 100 ft.” The discussion becomes a debate among engineers: Mr. Fteley attributes the high saturation to fine materials, while Mr. Craven argues that “porosity is merely a degree of compactness” and that water moves through the bank governed by the material’s porosity. Bassell lets these voices speak, using their disagreement to highlight the uncertainty in predicting seepage.

Calculating a Safe Profile: An Example

In Chapter VI, Bassell shifts from observation to calculation. He provides a worked example for designing a 100-foot dam with 90 feet of water, assuming a material weight of 125 lbs per cubic foot and a coefficient of friction of 1.00. The factor of safety against sliding is set at 10. This section is notably formulaic: Bassell lists assumed values, then derives the required base width. The exercise is meant to demonstrate how theory translates into a practical cross-section. Yet the reader is reminded that such calculations rest on assumptions—like the weight of material and the coefficient of friction—that may vary widely in real soils. The example is a tool, not a prescription.

Illustrations as Evidence: The Visual Argument

The book contains 31 figures, ranging from site plans to cross-sections to photographs. Bassell uses these images not as decoration but as integral evidence. For instance, Fig. 19 is described as “a graphical interpretation of the conclusion reached by the board of experts,” showing an ideal homogeneous dam with a dangerously high saturation plane. The caption notes that “the intersection of the plane of saturation with the rear slope … indicates an excessive seepage and a dangerously unstable condition.” Similarly, the photographs of the Tabeaud Dam (Figs. 6, 10, 13) document the actual construction methods—drains laid in trenches, embankment being placed—giving the reader a visual benchmark against which to measure the idealized diagrams.

Bassell’s study is best approached as a working engineer’s notebook: it gathers data from built dams, records expert testimony, and offers analytical methods without claiming final answers. Readers interested in the history of geotechnical practice will find the Croton Valley saturation studies and the Tabeaud Dam account particularly valuable. The book rewards those who read the figures as closely as the text.

Flicking through Bassell’s careful profiles of earth dams, I felt the patient, unsung hands behind each measurement. It reminded me of another kind of diligence, the quiet craft of engravers who gave shape to others’ visions—The Brothers Dalziel A Record of Fifty Years Work in Conjunction with many of the Most Distinguished Artists of the Period 1840-1890 — Text and Context. Both books honor the invisible labor that holds a grander design together.