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| Titel |
Road Sediment Production and Delivery: Processes, Rates, and Possible Improvements |
| VerfasserIn |
Lee MacDonald, Carlos Ramos-Scharron, Drew Coe, Alexander Stafford, Matthew Welsh, Abby Korte, Zamir Libohova, Ethan Brown, Cajun James |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077814
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| Zusammenfassung |
| Unpaved roads are increasingly recognized as one of the largest sources of anthropogenic
sediment in forested areas. For nearly 20 years we have been studying road surface erosion
and sediment delivery across widely varying environments in California, Colorado, and the
Caribbean. The objectives of this paper are to: 1) compare road sediment production and
delivery rates across different environments; 2) summarize the primary controls on
road surface erosion and sediment delivery; 3) estimate the relative contribution of
roads to watershed-scale sediment yields; and 4) suggest management practices
to minimize road sediment production and delivery. In our studies segment-scale
sediment production is measured with sediment fences, while detailed road surveys are
used to assess road-stream connectivity and estimating the contribution of roads to
watershed-scale sediment yields. Road-induced mass movements are not included
here.
Our mean road sediment production rates range from 0.1 kg m-2 yr-1 in snow-dominated
areas in California’s Sierra Nevada to 3.5 kg m-2 yr-1 in Colorado and 7.4 kg m-2 yr-1 on
St. John in the Caribbean. First-order controls on road sediment production are the amount
and type of precipitation, road gradient, road surface area, and surface cover, although
geology and soil type also can be important. Higher traffic levels can greatly increase road
sediment production by reducing the amount of surface cover, increasing the supply of
fine sediment, and increasing the propensity for rilling, particularly during wet
weather. Applying gravel can reduce road sediment production by a factor of 2-8
times by largely eliminating rainsplash and reducing rilling. Grading will at least
double road sediment production by increasing the supply of easily erodible fine
particles.
The percent of road length connected to streams also varies widely. In California only 3% of
the road length was connected in a snow-dominated area as opposed to 30% in a nearby
rain-dominated area. Connectivity was less than 20% in permeable volcanics in
California and coarse-textured soils in the Colorado Front Range. Road-stream
crossings accounted for most of the connected segments, as in temperate forests
drainage rills and sediment plumes rarely extend for more than 50 m. Few studies have
quantified the effects of unpaved roads on watershed-scale sediment yields, but in
northern California the estimated sediment yield was 1.4 Mg yr-1 per kilometer of
road, while in Colorado the long-term, chronic sediment production from roads was
estimated to be about 1 Mg km-2 yr-1. On St. John roads were estimated to increase
watershed-scale sediment production by 3-9 times, indicating that the road sediments are a
critical stressor to near-shore coral reefs. Relatively simple management actions
can greatly reduce sediment production and delivery from unpaved roads, but the
necessary improvements are constrained by the lack of political will and funding. |
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