EM 1110-2-1100 (Part V)
31 Jul 2003
(2) Literature review. Although groins have been around a long time and many references exist, most
only provide a few rules of thumb. No systematic methods for functional design under a wide range of
structural shapes, waves, and sediment transport conditions presently exist. Reviews for the functional design
of groins can be found in Bruun (1952); Bakker (1968); Balsillie and Berg (1972); Balsillie and Bruno
(1972); Nayak (1976) (unpublished); Tomlinson (1980); Fleming (1990); and EM 1110-2-1617. All these
reviews restate the same beliefs but fail to reference the sources that verify the concepts and conclusions from
theory, model studies (laboratory or numerical), or field experiments. As stated by Kraus, Hanson, and
"...the literature (on groins) may appear to assign validity to certain concepts and conclusions by
weight of repetition (but) not by independent confirmation." (p. 1329).
(a) Laboratory investigations suffered from severe scale distortions in sediment transport to cast serious
doubt and questions on their results.
(b) A fresh approach is needed that begins with a summary of over 20 parameters that govern beach
response to groins as listed in Table V-3-7 (from Kraus, Hanson, and Blomgren 1994). They are grouped into
three main categories (structure, beach, and hydrodynamic conditions), but the large number of variables
make analysis difficult. Missing from this table is the minimum, design beach width for shore protection.
Groin geometry and possible sediment size for the beach fill can be controlled in the design.
Main Parameters Governing Beach Response and Bypassing at Groins (from Kraus, Hanson, and Blomgren 1994)
Beach and Sediment
Waves, Wind, and a Tide
Depth at tip of groin
Wave height and variability
Depth of closure
Wave period and variability
Wave angle and variability
Configuration (straight, T, L, etc.)
Median grain size and variability
Orientation to the shoreline
Wind speed and variability
Spacing between groins
Wind direction and variability
Wind duration and variability
Note: Two integrated parameters governing groin functioning are the ratio of net to gross longshore sand transport, and the
presence, location, and number of longshore bars.
(c) From the previously listed review papers, other references and their own experience, Kraus, Hanson,
and Blomgren 1994 listed 13 functional properties attributed to groins and present a critical evaluation of
each as shown in Table V-3-8. The first five are well accepted properties that have led to the general rule of
the thumb to make the groin spacing to length ratio about two to four. However, this rule omits any
consideration of the cross-sectional shape of the groin. The length controls water depth at the end and, hence,
the amount of sediment by-passing around the tip. But the cross-sectional elevation in the swash zone
controls over-passing, the length and elevation on the beach berm control shore-passing, and the structural
materials control through-passing as takes place in rubble-mound and permeable groins. Tidal range,
predominant wave characteristics (height, period, direction), net and gross longshore sediment transport and
grain size are key hydrodynamic and sediment parameters. All these factors together produce the optimum
spacing and planform configuration of the shoreline within each compartment for average climate conditions.
Shore Protection Projects