Abstract
Most of the natural sciences make progress through a regular dialogue between theoretical developments and study cases or experimental works. By narrating the story of the Santa Cruz River, Robert H. Webb and colleagues clearly demonstrate the value of a detailed analysis of a particular system for understanding environmental changes. Indeed, in spite of the specificities of the Santa Cruz River, its history tells us a lot about current and historical relationships between rivers and society. It also has valuable lessons to impart about the resilience of socio-ecological systems.
To reconstruct the history of the Santa Cruz River, the authors mobilize a large range of historical data, including land surveys, natural surveys, newspapers, photographs and testimonies. Understandably, the earlier historical periods are less documented and there is some bias linked to available data, but all the sources are well presented and the limitations are honestly analyzed.
Requiem for the Santa Cruz has 11 chapters that state the issues explored (chapters 1, 2 and 3), develop the study case itself (chapters 4 to 10) and conclude (chapter 11). The book is richly illustrated, notably by many high quality photographs, and accompanied by abundant appendices (including, for example, species lists). It begins with the question of the downcutting process that affected many rivers in the southwestern United States during the end of the 19th century and the beginning of the 20th century. This morphological process can occur in a modest number of years, sometimes in a single flood, and had a great influence on both riverine ecosystems and societies (e.g. species loss, groundwater decrease, the Great Mesquite Forest changes). Thus, the opening chapter introduces the issues of river changes, social consequences and identification of causes that are a classic pool of themes for fluvial hydrology and geomorphology.
After this, the authors draw a portrait of the Santa Cruz River (chapter 2), a semi-arid system with some intermittent reaches, which is very sensitive to hydrological drivers. They also review the list of potential causes of downcutting in southwestern rivers (chapter 3), such as livestock grazing, land-uses changes, drought and floods.
The main section of the book is dedicated to an examination of changes to the river through space and time to disentangle natural and human influences and responses. To do this, the authors logically follow a chronological plan from the 18th century to the present. After a presentation of the situation before the 1870s, covering the arrival of Spanish explorers and missionaries (chapter 4), a more substantial section focuses on the 1870s and the 1880s. This period was characterized by important changes in both society (“from the Wild West to a semblance of modernity”) and hydroclimatic conditions (increased rainfall and flooding) (chapter 5). The former changes notably generated an increase in water demand all along the river. The latter served to initiate the major morphological changes that mainly occurred in the 1890s: the downcutting and widening of the Arroyo (chapter 6). These changes are also detailed in terms of their perception by society and the technical responses to new conditions such as groundwater decline. The remaining four chapters develop the history of the river during the 20th century from Arroyo development to river restoration.
This book is best read in its entirety because each period of the river’s history provides a new piece of a complex puzzle, and altogether it is an excellent illustration that river systems follow complex trajectories that may combine many contingent and stochastic influences: an earthquake in 1887, woodcutting, agricultural clearing, urban sprawl, changes in flood frequency and precipitation, changes in grazing activities and of technical systems for water uptake, and so on. Most of these factors are related, directly or indirectly, and each change generates important responses, such as bank stabilization measures to counteract erosion resulting from downcutting or changes in water source. The historical perspective presented here clearly and usefully shows that complexity.
Requiem for the Santa Cruz further demonstrates the value and interest of historical analysis for current management issues, such as flood risk and riverine ecosystem management, because it highlights the legacy of fluvial system history on present conditions. Alongside this is a clear relation of channel and land-use changes to riverine habitat ecosystems, which play an important role in such semi-arid systems; indeed, The Great Mesquite Forest is particularly significant in terms of biological conservation, and the river and its history are intimately tied to the fate of the forest itself.
In spite of all the qualities of the book, a small frustration comes towards the end. Indeed, with all the data and the knowledge put together by the authors it would have been useful to present a synthetic scheme that represents the dynamics of the characteristics of the Santa Cruz River (drivers, states and functioning). It would have allowed for generalization and discussion about the reversibility of fluvial system changes. Instead, some discussion about resilience is quickly handled on the last page, whereas it underlies the entire book and really deserves greater development. Indeed, the term Requiem refers to the death or to the remembrance of some victims, and is associated with an idea of irreversibility. It seems that the authors aimed to testify to the memory of a riverine victim of unsustainable water development, but the strength of the testimony would have been reinforced by placing the case study within a wider conceptual framework. The scientific material and data is certainly there to do that.
Although the Santa Cruz River is a specific system, it shares many common characteristics with numerous rivers around the world such as diversification and increase in environmental and societal pressures over recent centuries. Thus, this case study gives some very interesting ideas about the dynamics and management of constrained environments. Notably, it shows how the combination of various changes and drivers influences fluvial systems at a level that is mainly irreversible at the time scale of contemporary human management. This history is essentially a showcase of the story of modernity.
Overall, a substantial amount of information has been synthesized by the authors and, in spite of the absence of some generalization that would have helped set the work in a wider context, it is a very useful read for river managers, researchers and naturalists interested by the co-evolution of water uses, riverine ecosystems and an historical analysis of the environment.