How Does Flow Alteration Propagate Across a Large, Highly Regulated Basin? Dam Attributes, Network Context, and Implications for Biodiversity
This study examined the highly regulated Colorado River Basin (CRB) to understand how flow alteration propagates in river networks, as influenced by the location and characteristics of dams as well as the structure of the river network—including the presence of tributaries.
We used a spatial Markov network model informed by 117 upstream-downstream pairs of monthly flow series (2003–2017) to estimate flow alteration from 84 intermediate-to-large dams representing >83% of the total storage in the CRB. Using Least Absolute Shrinkage and Selection Operator regression, we then investigated how flow alteration was influenced by local dam properties (e.g., purpose, storage capacity) and network-level attributes (e.g., position, upstream cumulative storage). Flow alteration was highly variable across the network, but tended to accumulate downstream and remained high in the main stem. Dam impacts were explained by network-level attributes (63%) more than by local dam properties (37%), underscoring the need to consider network context when assessing dam impacts.
Our results advance the notion that basin-wide reoperation should be considered in any effort to mitigate flow alteration—a critical need in light of new damming in developing economies. Understanding which critical infrastructure and locations in the network are more impactful could help guide the prevention or mitigation of flow alteration impacts more effectively. Modeling efforts such as this study, combined with the increasing availability of flow and biodiversity time-series data, have great potential to advance the study of flow regime restoration at the river network level and, thus, more effective river ecosystem conservation.
Despite long-standing efforts to reduce the impacts of dams on river biodiversity and ecosystem processes, our understanding of how altered flow regimes propagate in river networks is incomplete. Here we used the Colorado River Basin as a model system to examine how dams alter flow regimes, individually and cumulatively, as water flows downstream a river network. We found that impacts accumulated downstream and tributaries could not reset natural flow variation in the lower main stem. Although local dam properties (e.g., storage) were important in determining how impactful individual dams were, spatial context (location in the network and upstream regulation) was paramount.