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 fishpassage 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