Ecohydrology and Fish-Passage Engineering: Legacy of Denil and the Call for a More Inclusive Paradigm

Ralph Waldo Emerson famously said that “language is a city to the building of which every human being brought a stone.” We can appreciate the imagery and the message: language evolves and does so in response to the needs of its users. Like water, language is fluid. It resists static form. It can be clear or murky. The use of language has changed in response to our evolving society. Terms such as “slide rule” fall out of common usage because the objects they describe are no longer in common use. Conversely, we can all think of everyday words that were rarely used 30 years ago (e.g., cell phone, biodiesel). The lexicon of science and engineering is no different. Obsolete scientific terms fade away, whereas others are created to help concisely define a new concept or technology. Apropos of both water and language, the definition of ecohydrology has received considerable attention from those working in the myriad subdisciplines that arguably comprise this field. But does the description of ecohydrology encompass fish-passage engineering and similar engineering efforts related to fish passage such as stream restoration, road ecology, and dam removal? We suggest that their inclusion is not only appropriate but recognizing these pieces as part of a unifying paradigm may also very well help foster the interdisciplinary cooperation that these fields demand.

A spirited debate on the meaning of ecohydrology is under way. The proposed definitions range from the specific to the inclusive. For example, Baird and Wilby (1999) restrict the term to the study of plant-water interactions. Rogriquez-Iturbe (2000) concisely defines ecohydrology as “the science which seeks to describe the hydrologic mechanisms that underlie ecologic pattern and processes.” Nuttle (2002), however, suggests that ecohydrology is the “subdiscipline shared by the ecological and hydrological sciences that is concerned with the effects of hydrological processes on the distribution, structure, and function of ecosystems, and on the effects of biotic processes on elements of the water cycle.” For those preferring a broader interpretation, Nuttle’s (2002) characterization is appealing because it acknowledges the two-way relation between water and ecosystem rather than one focused on ecological responses to hydrologic mechanisms. Wood et al. (2008) document the struggle between the specific and generalist definitions for both ecohydrology and hydroecology but acknowledge that “there is arguably no single accepted definition of either term, never mind a joint definition.” In the end, the word’s etymology—a simple combination of ecology and hydrology—may serve as the most general definition for ecohydrology: a subdiscipline lying at the interface between ecology and hydrology.

This simple interpretation of ecohydrology is compelling because it is inclusive. Varied but interrelated topics such as evapotranspiration, river restoration, and fishway engineering can be found at the interface between hydrology and ecology. In fact, the latter two topics may be categorized under ecohydraulics, a recognized subdiscipline of ecohydrology (Wood et al. 2008). Whereas ecohydrology deals with the overarching relation between water and ecosystems at the catchment scale, ecohydraulics focuses on the interplay between traditional hydraulics and the surrounding environment. Nestler et al. (2008) succinctly describe ecohydraulics as a combination of the “basic principles of biology and ecology and hydraulic engineering.” Those very principles are incorporated in nearly all fishways ranging from simple baffled chutes to complex mechanical fish lifts. It seems that fishway engineering, a blend of fisheries science and hydraulic engineering, is a quintessential example of ecohydraulics, and so, by extension, may be labeled as ecohydrology. If so, is ecohydrology an esoteric specialization for water resource engineers or an increasingly relevant part of their core skill set? Current trends in ecohydrology and fish-passage engineering are perhaps best understood in the context of the history of public policy on fisheries.

Interestingly, the history of fishways is rooted in the common law of ancient times. In sixth-century Rome, legal precedent regarding fishing was first established when an enterprising landowner attempted to retain tuna fishing rights upon the sale of his estate. However, a subsequent judgment effectively negated the contract because a private right could not be imposed upon the sea, which “by nature it is open to all.” This profound ruling, codified in the Digest of Justinian, is regarded as the first recorded reference to a public right to fish (Appleby 2006). Whereas §33 of the Magna Carta is often cited as the basis for this public right, that statute actually calls for the removal of fish weirs “from the Thames, the Medway, and throughout the whole of England, except on the seacoast” to facilitate navigation—it does not directly support the public’s right to fish. Nevertheless, the inclusion of a clause to remove fish-trapping devices in England’s “Great Charter” exemplifies the long-standing tension between those advocating for the public resource (e.g., fishery) and those advocating private use of waterways (e.g., navigation, weirs). Perhaps most important, this statute helped establish the sovereign’s authority to govern the use of those resources and to protect the public interest in the fishery. As a result, the miller was often required to provide migrating fish with a means of passage over the dam at his own expense. This requirement was later established as an English common law known as “right of fishery” and was held in the public trust. As North America was colonized, this common law transferred. When granted land rights by the Crown, settlers were required to abide by the right of fishery by providing fish passage—or otherwise mitigate any obstructions to fish passage—at the landowner’s expense or compensate upstream abutters for the loss of fishery (Odeh 1999). The foundations of this common law were frequently challenged, but in the eighteenth and nineteenth centuries, several important court decisions reaffirmed that fisheries are a publicly held interest and that dam owners must protect the resource by providing fishways at their own expense.

Several hundred years ago, one such challenge was made famous in Falmouth, Massachusetts. Grist mills built in the early 1700s on Falmouth’s Coonamessett River were decimating an important herring run. In response, legislation requiring fish passage was passed in the 1790s. In 1805, the dispute escalated when, in a protest on Falmouth’s Village Greene, supporters of the mills loaded a cannon with herring and attempted to fire it. However, the gunner was killed in the explosion, thus ending the so-called “herring war” (Friends of Falmouth Farms, Inc. 2011). Future challenges were more civil. In the mid-1800s, the Commonwealth of Massachusetts legislature required fish passage, as prescribed by County Commissioners, in its charter to the Essex Company (builders of the first dam on the Merrimack River at Lawrence). During this period, dams continued to be built throughout the country, and many other states passed legislation requiring fishways at dams. This issue was not limited to coastal states. In 1884, in Parker versus the people of the State of Illinois, dam owner William Parker was prosecuted for not providing fish passage in accordance with an 1879 statute. Parker, who had owned the dam since 1871, claimed an exception under a grandfather clause. However, the State Supreme Court upheld the statue stating that “the fish being the common property of the people” cannot be obstructed by the dam owner (Beck, unpublished conference paper, 2009). Fish-passage cases eventually reached the U.S. Supreme Court. In 1872, in Holyoke Company versus Lyman (82 U.S. 500), the high court ruled that the dam owner must not only compensate upstream riparian land owners for loss of fishery and related property value but also provide fish passage at the owner’s expense. During this period, more barriers were constructed to meet society’s needs and in response, many states passed legislation requiring fishways. Federal legislation followed in the twentieth century. Notably, the Dam Act of 1906 granted authority to the government to require fishways at dams under federal jurisdiction. In 1920, Congress passed the Federal Power Act, which provided the Secretaries of the Interior and Commerce with prescriptive authority over the construction, operation, and maintenance of fishways at federally regulated hydroelectric projects. The Fish and Wildlife Coordination Act, passed by Congress in 1934, required federal agencies to consult with the Bureau of Fisheries (now the U.S. Fish and Wildlife Service) to determine whether fishways and other aids to fish migration would be necessary and economically practical at dams. In 1972, Congress passed the Clean Water Act, which was instrumental in providing states with the authority to prescribe fishways at developments requiring water-quality certification. In 1973, Congress passed the Endangered Species Act, under which fishways have been installed and operated for species listed as endangered or threatened. Collectively, these many statutes form the federal basis for the legal requirement for fish passage in the United States today.

Not surprisingly, these legal requirements to pass fish helped fuel the science of fishway engineering. Odeh (2000) documents fishway developments more than 300 years old. Clay (1995) notes that efforts to provide passage over mills and natural obstacles likely predate even those earliest recorded works. However, fishway design did not become a recognized branch of hydraulic engineering until the mid-1800s, following the growth of the water-power industry (McLeod and Nemenyi 1941). Through the nineteenth century, French, American, and Norwegian investigators all developed and tested a variety of baffled-chute and pool-and-weir fishway designs. These designs were on the basis of maximizing energy dissipation and reducing velocities in the fishways through jet deflectors. However, lacking a modern scientific approach to the investigation, these early researchers met with very limited success. A Belgian scientist named Denil from 1908 to 1938 advanced the field by performing systematic research in fishway design. His novel methods included fish counts to measure passage effectiveness, thus advancing an interdisciplinary approach decades before the term was actually first coined. Unlike his predecessors (and regrettably many successors), Denil sought to move fish, not just water. His seminal work was highly influential and was later modified by others, eventually culminating in the Denil and Steeppass designs successfully used on many waterways today. Of course, other researchers have played significant roles in the development of fishways, but Denil’s fruitful work is illustrative of the initial efforts in a long historical trend toward more interdisciplinary research in fishway engineering.

One hundred years after Denil’s initial efforts, engineers and biologists often work in concert to design passage facilities that reconnect fish with their habitat in waterways throughout the country. As a result, many migratory fish species are expanding in their historic ranges. Nevertheless, the remaining challenges are daunting. Vast numbers of barriers to fish migration persist. On the East Coast, thousands of abandoned milldams interrupt the historical spawning routes of once thriving populations of Atlantic salmon and American shad. In the continental United States, there are over 82,000 documented dams (U.S. Army Corps of Engineers 2009) and 2 million culverts, most not designed for fish passage. Even where passage facilities were designed to meet a primary life-cycle need (i.e., spawning) for specific target species, many projects fail to provide for the entire aquatic community’s suite of biological needs (e.g., rearing, feeding, maturation, dispersion, and seasonal use of habitat). To be sure, these issues are present throughout the world in which societies struggle to balance a growing need for hydropower and the ethical, economic, and historical obligation to protect and conserve diminishing fisheries. These challenges are potentially compounded by the environmental impacts of climate change, which are both ubiquitous and unclear. This much is clear: the uncoordinated, single-discipline efforts (and consequent errors) of the past cannot be repeated. If solutions are to be found at the interface of different sciences, then topics like ecohydrology are, indeed, increasingly relevant components of engineering education. One may wonder—are government, industry, and academia doing enough to advance Denil’s legacy and promote true interdisciplinary development of engineers working in the field of fish passage?

Most practitioners do assemble work teams with a diverse skill set; however, these teams tend to be more multidisciplinary than interdisciplinary. Engineers on such teams often lack the basic ecological literacy to assimilate the behavioral limitations and biological needs of migratory fish and then incorporate those constraints into design methodologies. Hydraulics must be linked to ichthyomechanics. Watershed hydrology must be understood in the context of seasonal migration. Fluency in physics must be complemented by a working knowledge of biology. To be sure, such literacy can be gained through experience, but experience is costly—costly to the fisheries resource itself. At the risk of extending the financial analogy too far, we suggest that true interdisciplinary engineering education and research into fish passage would pay dividends.

There have been notable successes. In decades past, Dr. John (Jack) Orsborn, professor emeritus at Washington State University, and his contemporaries educated many talented engineers working in fish passage today by stressing that the field needed “integrators, not specialists.” Orsborn’s maxim succinctly expresses the interdisciplinary nature of fish-passage engineering, ecohydraulics, and ecohydrology. More recently, the Bioengineering Section of the American Fisheries Society proposed an ecologically focused curriculum for engineers (Whitman et al. 2006). This proposal was successfully approved by the Curriculum Working Group in January 2006 and disseminated in their white paper entitled “Engineering for Restoration of Rivers and Improved Ecological Systems.” These efforts, as well as the authors’ own involvement in a new program at the University of Massachusetts, Amherst, were on the basis of recognition of a need for engineers with interdisciplinary training. Continuing successes in the advancement of interdisciplinary fish-passage engineering curricula will require forward-looking academic institutions that can work seamlessly across disciplines. We anticipate and encourage an active debate that may help shape these programs.

Efforts to solve the complex environmental issues of today are increasingly interdisciplinary. Fish-passage engineering is an example of a field that has suffered through a history of technical myopia but now stands poised to benefit from a previously unseen level of scientific collaboration. Optimism for the future abounds, but challenges remain. Principal among many needs is additional support for research into fish-passage design and effectiveness. Moreover, widespread acceptance of an inclusive definition of ecohydrology may help dispel professional territorialism; further unify the efforts of disparate disciplines under that common banner; and focus more attention on combining key aspects of fish biology and behavior, hydraulics, and hydrology. We would like to think that Emerson, that old “sage of Concord” who was so well known for his writings on the intricacies of nature and man’s dependence on it, would readily approve.

Disclaimer: The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service.