Download Emily Shimada WLF 400 Project Proposal Evaluating the Physical

Emily Shimada
WLF 400
Project Proposal
Evaluating the Physical Impact of Mining
Background
Accelerated soil erosion and sediment production that occurs from direct or indirect human activity is a
significant problem worldwide. Land use and cover changes like mining, deforestation and agriculture
practices can have drastic impacts on sediment introduction, transfer, storage, and yield in fluvial
environments. Altered rates of sediment can have both physical impact on the stream, and ecological
impacts through habitat alteration. The recovery of fluvial environments can take up to several hundred
years (Charlton 47).
The two primary types of sediment transfer in fluvial systems are coarse grain and fine grain sediment,
which have notable differences in behavior and affect that. Coarse grain sediment is transported along
the channel bed as the bedload. The mechanism for the bedload is called saltation, and refers to grains
that are generally greater than 0.062mm and are too heavy to be carried in suspension. The sediment
will therefore roll, slide or bounce alone the channel bed. Alterations in coarse grain sediment can cause
the water level to fluctuate, increase flooding, and change the channel dimensions (Dunne and Leopold
669).
Fine grain sediment is carried in suspension, and referred to as the suspended load. Suspended loads
carry clays, silts, and sands, and are categorized into wash loads and dissolved loads. The dissolved load
encompasses particles that are transported in solution. The wash load makes up the finest fraction of
the suspended load, consisting of clay particles with a diameter less than 0.062 mm (Charlton 67). The
tiny clay particles are able to remain suspended and transported at very low velocities and may be
carried over a long distance in a short amount of time. Wash loads are transported in suspension at
approximately the same speed as the flow, therefore the rate of wash load transport is determined
primarily by the rate of fine-grain sediment supply to the fluvial system (Knighton 123). High
concentrations of wash load (>20%) increase the viscosity of flow and reduce settling velocities. This
enables the transport of coarser grains and increases the bed-material load, further altering the natural
condition of the river or stream (Knighton 125).
Tropical mountain ecosystems with steep topography, like those in Ecuador, are sensitive to
environmental change from both natural and anthropogenic processes. Land use changes often
exacerbate the rate geomorphic activity like soil erosion, landslides and fluvial activity (Larson et. al
204). Southern Ecuador has experienced demographic growth over the past few decades, which has lead
to increases in land use and land cover changes like deforestation, agriculture land conversion, mining,
and development of roads, trails and infrastructure. This growth is accelerating environmental change
and putting pressure on fluvial systems through the introduction of high volumes of sediment (Vanacker
et al).
Mining operations generate large volumes of waste sediment, which can easily enter rivers and streams
if not managed properly. The Mining industry in Ecuador has existed for over 500 years, but spiked
considerably in the 1980’s. This spike was due to an increase in small-scale and artisanal mining, which is
still the primary type of operations in existence today (Appleton et. al). The predominant factor that
distinguishes small-scale and artisanal mining practices is annual production, which is less than 100,000
tons of ore (Cifuentes 5). The majority of small-scale mining operations are unregulated, and dispose
mine tailings and waste directly into ambient rivers and streams. Small-scale miners are typically
financially unable to invest in environmental protection, and tend to lack general safety and
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Emily Shimada
WLF 400
Project Proposal
environmental information. The resulting environmental impacts often manifest downstream of mining
sites, preventing the miners from seeing the impacts directly (Tarras-Wahlberg 168).
The mining operations in southern Ecuador are increasing rates of erosion and sediment introduction
into fluvial systems. The current practices are producing adverse effects on the physical characteristics
and biological functions of the ambient fluvial systems in southern Ecuador (Appleton et. al 32). The
Calera River and Amarillo River in the Portovelo-Zaruma district are one depiction of the ecological
effects of mining activity. The Amarillo River exhibits diminished aquatic invertebrate and fish species
life downstream from mining operations relative to pristine, upstream regions. The Calera River is
referred to as a ‘dead river’ downstream of mining activity with no fish or invertebrate life present
(Tarras-Wahlberg 167).
The introduction, transport, and deposition of fine sediment can have significant consequences for
stream organisms (Larson et al. 204). The presence of fine grain sediment can increase water turbidity,
which reduces the depths of sunlight penetration and hinders the rate of photosynthesis (Dunne and
Leopold 715). Fine grain sediment deposition causes the interstitial spacing within river gravels to
become filled. Interstitial spacing is crucial for biotic activity. The spacing functions as a habitat for many
invertebrate species, and as spawning grounds for many fish species (Charlton 65). Large suspended
loads can also have physical impacts on the stream dimensions by altering the stream course and
influencing floodplain development through overbank deposition (Knighton 125).
Quantitative understanding of the physical and ecological effects of sediment transport, and the
corresponding mechanisms are still fairly uncertain. Identifying the specific source of sediment in a
single location is difficult because there are often multiple natural, anthropogenic, direct and indirect
mechanisms involved. The complexity of interactions among the different possible mechanisms makes
it difficult to accurately distinguish the anthropogenic sources and associated ecological impacts of fine
grain sediment (Larson et al. 204). The transport and deposition trends of suspended sediments are a
function of many environmental variables, including channel dimensions, climate, topography,
landscape morphology, vegetation cover and composition, and sediment composition, texture and
volume (Vanacker et al. 65). Establishing the influence of mining and other land uses on streams in
southern Ecuador is necessary in order to determine if they are causing significant physical and
ecological impacts.
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