Melinda Snodgrass Bibliography Maker

Melinda Snodgrass studied opera at the Conservatory of Vienna in Austria, graduated from U.N.M. with a degree in history, and went on to Law School. She practiced for three years, and discovered that while she loved the law she hated lawyers so she began writing science fiction novels.

In 1988 she accepted a job on Star Trek: TNG, and began her Hollywood career where she has worked on staff on numerous shows — Reasonable Doubts, Profiler, and has written numerous television pilots and feature films. Presently she is the Executive Producer on the upcoming Wild Cards TV series. She is also the co-editor and writes for the Wild Cards series with George R.R. Martin.

In the prose world she has finished the third book in her five book Space Opera series for Titan Books and is working on book 4. Book 1— THE HIGH GROUND was published in July 2016, book two IN EVIL TIMES will be released July 2017. She's can't say she's enjoying how fragile women's rights actually are, but she is fascinated with that issue as well as issues of class and how it effects governments.

The three books in the EDGE series which explore the war between science and rationality and superstition and religion — THE EDGE OF REASON, THE EDGE OF DARKNESS and THE EDGE OF DAWN are currently available from Tor and Titan Books.

For fun she rides her dressage horses, plays video games and spends a lot of time in the gym.

Abstract

Billions of dollars are being spent in the United States to restore rivers to a desired, yet often unknown, reference condition. In lieu of a known reference, practitioners typically assume the paradigm of a connected watercourse. Geological and ecological processes, however, create patchy and discontinuous fluvial systems. One of these processes, dam building by North American beavers (Castor canadensis), generated discontinuities throughout precolonial river systems of northern North America. Under modern conditions, beaver dams create dynamic sequences of ponds and wet meadows among free-flowing segments. One beaver impoundment alone can exceed 1000 meters along the river, flood the valley laterally, and fundamentally alter biogeochemical cycles and ecological structures. In this article, we use hierarchical patch dynamics to investigate beaver-mediated discontinuity across spatial and temporal scales. We then use this conceptual model to generate testable hypotheses addressing channel geomorphology, natural flow regime, water quality, and biota, given the importance of these factors in river restoration.

Private and public agencies across the United States spend billions of dollars on river restoration (Bernhardt et al. 2005) in attempts to return targeted systems to a state similar to that before disturbance. Our understanding of the predisturbance system, however, is framed by recent human alterations (e.g., Walter and Merritts 2008). To successfully implement a project that achieves even partial restoration, it is essential to understand the baseline conditions (Wohl 2005).

The baseline typically used in river restoration is a continuous, free-flowing system (FISRWG 1998). However, in catchments with limited modern human impact, the presumed continuity of headwaters is fragmented by bedrock, colluvium, large wood, past glacial souring and deposition, and North American beaver (Castor canadensis) dams (Naiman et al. 1988, Ballantyne 2002, Benda et al. 2005), among other discontinuities. These components increase longitudinal heterogeneity by generating a stepped channel-bed profile in place of the continuous slope of the reference condition, with shallower gradients, slower velocities, and the accumulation of sediment upstream of blockages, and with scouring downstream of them. River discontinuities increase lateral heterogeneity by maintaining upstream floodplains, scouring additional downstream channels, and causing channel avulsions.

River obstructions and their impacts also vary over time, with the temporal scale depending on the type of discontinuity. Bedrock discontinuities are created and destroyed at the longest time scale. Glacial scouring and deposition occurs within the temporal and spatial discontinuities set by bedrock. Following glacial retreat, paraglacial modification continues for tens of thousands of years (Ballantyne 2002). Sediment, debris, and beaver dams modify the river corridor at a still smaller scale, with creation and destruction by stochastic events such as fire and floods (Benda et al. 2004) and beaver activity, and time scales of persistence as short as years to decades.

These discontinuities have been largely removed from rivers in the United States through recent human activities such as bedrock blasting, debris-dam removal, other channel homogenization for log drives, placer mining, logging of forests that once supplied major debris dams, beaver trapping, and floodplain reclamation (Lichatowich 1999, Wohl 2005). Many of the remaining preexisting discontinuities have been modified—and new ones created—by human dam and road construction. For example, table 1 compares beaver dams with run-of-the-river human dams; run-of-the-river dams are the most common existing and removed dams in the United States (Poff and Hart 2002). However, rather than viewing human discontinuities as modifications of preexisting ones, restoration efforts typically view human dams and roads as features that disrupt otherwise continuous systems.

Table 1.

Comparison of beaver and run-of-the river human dams as an example of human-built replacement of one type of preexisting discontinuity along the river corridor.

Parameter Run-of-the-river human dam Intact beaver dam 
Permeability Impermeable Leaky or somewhat permeable 
Structure longevity 100 to 1000 years 10 to 100 years 
Number of spillways or downstream channels One One or more 
Crest geometry Simple, usually linear Complex, irregular 
Hydraulic cross section at the spillway crest Uniformly fast and shallow  Variable, with concentrations of faster and deeper water, often with multiple spillways; flow may be entirely through the dam 
Low-flow water passage Little to no release Water continues to leak through dam 
Upstream water level variability Little to none Variable over the water year 
Upstream littoral zone Narrow Wide 
Parameter Run-of-the-river human dam Intact beaver dam 
Permeability Impermeable Leaky or somewhat permeable 
Structure longevity 100 to 1000 years 10 to 100 years 
Number of spillways or downstream channels One One or more 
Crest geometry Simple, usually linear Complex, irregular 
Hydraulic cross section at the spillway crest Uniformly fast and shallow  Variable, with concentrations of faster and deeper water, often with multiple spillways; flow may be entirely through the dam 
Low-flow water passage Little to no release Water continues to leak through dam 
Upstream water level variability Little to none Variable over the water year 
Upstream littoral zone Narrow Wide 

View Large

Recent beaver recolonization provides an opportunity to examine one of the major discontinuities once present in rivers. Beavers create a shifting mosaic (sensuStanford et al. 2005) of free-flowing, impounded, and meadow habitats (see examples in figure 1), the last two of which can dominate a river network (Naiman et al. 1988). Of these, beaver impoundments have been well studied at the reach and segment scale. When compared with a modern free-flowing reference, they alter hydrologic and sediment transport regimes (cf. Pollock et al. 2003), biogeochemical cycles (Correll et al. 2000), and habitats (cf. Rosell et al. 2005).

Figure 1.

Examples of headwater segment types classified in this article: (a) free flowing, (b) beaver meadow, (c) valley beaver impoundment, and (d) in-channel beaver impoundment.

Figure 1.

Examples of headwater segment types classified in this article: (a) free flowing, (b) beaver meadow, (c) valley beaver impoundment, and (d) in-channel beaver impoundment.

Although beaver impoundments are well studied, little research has been conducted on the role of beaver meadows in catchment processes, although these features may be dominant in the headwater network (see discussion below). Additionally, the literature does not examine the cumulative, serial impacts (sensuWard and Stanford 1983) of beaver-generated discontinuities. This lack of research is in spite of the density of beaver dams reaching 3 per 100 meters (m) locally (Burchsted et al. 2009) and 10 per kilometer at larger scales (Pollock et al. 2003), and despite the importance of understanding processes at large scales for effective restoration (Palmer 2009). Additionally, understanding of the effects of beaver dams has not yet been applied to the many enterprises of river restoration, despite the impact of these dams on the processes targeted for restoration. Lastly, beaver dams are one of the many types of discontinuities altering river networks, and we use them in this article as a ubiquitous and well-defined example. We need to scale up our understanding of fluvial discontinuity to add additional information to the body of literature, and to apply this research to river restoration design.

This article presents a framework to guide future research by considering beaver-created features in headwaters. Headwater streams up to the fourth order in size account for 60% to 80% of miles in a river network (Benda et al. 2005). Because they control the sediment supply and strongly influence the biotic diversity of river networks (Meyer et al. 2007), they are important for restoration. In order to incorporate discontinuity into the headwater restoration baselines at appropriate scales, we present a discontinuous, hierarchical, patch-dynamics conceptual model (sensuWu and Loucks 1995, Poole 2002).

In this model, beaver impoundment and meadow habitats are patches generated by the physical discontinuities of intact and breached beaver dams, respectively. These patches store and release water and sediments—with storage or release depending on the habitat type, season, and climatic conditions—resulting in a stepped longitudinal profile of the flux of these materials. Beaver dams may also limit organism movement, and they generate discontinuities in the longitudinal oxygen profile that modify biogeochemical cycling along the river corridor.

To apply the concept of longitudinal discontinuity to river restoration, we first consider the existing reference condition most commonly used in restoration design. We then describe the theoretical stream ecology literature beyond the river restoration reference, and build on the body of literature to create our conceptual model. Finally, we use our model to generate testable hypotheses that can guide future research, focusing on the major processes addressed by river restoration. We conclude by describing potential specific applications in restoration projects.

Current river restoration view of headwaters

River restoration priorities and designs commonly view rivers as equilibrium systems determined by local physical conditions, stripped of the complexities of multiple possible equilibrium states created by biological—particularly human—influences at scales beyond the site (Palmer 2009). The common practice of basing restoration design on physical reach-scale reference conditions is founded in this misperception. These reference conditions are derived from the river continuum concept (RCC; Vannote et al. 1980) and the longitudinal profile zones described by Schumm (1977), generating the vision of a continuous, free-flowing river (FISRWG 1998). Therefore, reference headwaters are narrow water bodies with higher gradients, larger mineral sediments, higher water velocities, organic matter dominated by terrestrial inputs, and a nearly closed forest canopy, and they are part of a continuous gradient from headwaters to mouth.

An example of reference-based restoration is shown in figure 2, a previously impounded reach shown one day after dam removal. In this case, a reference reach was selected from the same watercourse and the sediment impounded by the dam was removed as needed to create a channel as similar as possible to the reference—a common design practice (Pizzuto 2002). Additional design factors included channel and bank stability, longitudinal connectivity, and hydraulic conditions favorable for fish passage.

Figure 2.

Example of a dam removal approximately one week following removal. View is facing upstream from within the area of the removed dam. White arrows mark the remaining abutments of the original dam face. The channel has been created by removing impounded sediment to match the shape of a downstream reference reach. Cobble substrate placed on the streambed will resist erosion in accordance with sediment transport theory. The banks are cut to a stable slope, stabilized at the base with large cobbles, and seeded with native vegetation. Compare with the channel in figure 1b.

Figure 2.

Example of a dam removal approximately one week following removal. View is facing upstream from within the area of the removed dam. White arrows mark the remaining abutments of the original dam face. The channel has been created by removing impounded sediment to match the shape of a downstream reference reach. Cobble substrate placed on the streambed will resist erosion in accordance with sediment transport theory. The banks are cut to a stable slope, stabilized at the base with large cobbles, and seeded with native vegetation. Compare with the channel in figure 1b.

In comparison, the analogous beaver dam failure creates a beaver meadow, where the channel cross section is visibly narrower and deeper than the upstream or downstream reference on the same river (figure 1b). Since the channel in the meadow erodes out of previously impounded sediments, the bed is generally finer in size than the reference. Scattered cobbles on the bed surface, the result of bed coarsening, demonstrate the trajectory of the channel as it transitions to a state similar to the reference. Although the channel is actively eroding, most of the impounded sediments remain vegetated in place in the riparian zone.

Without valuing one system over the other, we note that these two channels are fundamentally different. The differences can be traced in part to the emphasis of human dam removal on longitudinal connectivity of water and sediment. In contrast, beaver dam failure creates a relatively small breach in the dam; the remaining dam structure continues to impede high flows, and the eroding channel provides a source of sediment. Additional disparities in channel form are caused by differences in the discontinuity of the barriers before removal or failure (table 1). In order to select the appropriate reference condition for dam removal, it is necessary to understand the role of these different reach types at the catchment scale.

The issue of scale is further apparent when considering the common assumption that increasing heterogeneity at the reach scale increases species diversity, a belief that is largely unfounded (Palmer et al. 2010). The failure of this assumption in practice can be traced, in part, to its application at the incorrect scale. When scale is increased and multiple habitat types are included at the network scale, species diversity increases (Wright et al. 2002), but this understanding has not been applied to river restoration.

The forested headwater paradigm

In addition to providing a foundation for river restoration design, the RCC has generated decades of research and theoretical advances. The longitudinal gradient of the RCC has been expanded to allow for lateral (Junk et al. 1989) and subsurface (Stanford and Ward 1993) continuity, and has given way in part to longitudinal discontinuity generated by geologic features and physical processes (Montgomery 1999, Benda et al. 2004). Discontinuity creates patches, and relatively homogenous, distinct patches with clear boundaries interact longitudinally, laterally, and vertically (Pringle et al. 1988

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