Jon,
I put something together some time ago. I will post it for you. I updated a few things and checked the links.
The soil transport of the Mississippi has been studied many times. So this will supply some good data for us.
http://oai.dtic.mil/oai/oai?verb=getRec ... =ADA460627‘The Lower Mississippi River, extending from Cairo, Illinois to the Gulf of Mexico, annually transports approximately 170 million tonnes of sediment. Historically, the quantity and calibre of sediment derived from catchment erosion have been affected by changes in land-use and management. For example, soil erosion increased during the 19th and early 20th centuries due to settlement by Europeans and this may have elevated catchment sediment supply to the Mississippi River, while more recently the supply of sediment from tributaries is known to have decreased markedly as a result of river engineering and management. Specifically, the construction of large dams as part of the Mississippi River and Tributaries (MR&T) Project has trapped sediment that would otherwise have been supplied to the Mississippi, particularly by the Missouri River.”
So we have a number for today but we know it has been greatly affected by man. So some more searching.
http://www.cep.unep.org/publications-an ... -river.pdfPeriod of record kg km−1 year−1 Source
<1850 ? –
1879 to 1880 107 297 Fisk (1952); estimate 1
1879 to 1880 102 691 Fisk (1952); estimate 2
1851 to 1930s 117 933 postulated in Curtis et al. (1973)
circa 1890s 94 220 Dole & Stabler (1909)
1949–1961 85 463 Judson & Ritter (1964)
1956–1967 90 600 Curtis et al. (1973)
1963–1979 64 201 Milliman & Meade (1983)
1970 to 1988 65 380 Keown et al. (1986)
1980 to 1988 33 975 Smith et al. (1996)
1974 to 1993 52 347 This study
Now at this point we have to pick a number that represents the transport less human intervention. Current levels times three may be reasonable.
So back to:
http://www.kgs.ku.edu/Hydro/Ponds/smithEA_2005_hi.pdf“Our estimate for
sediment discharge from the MS Basin (161 x 10^6 t/
year) is within 4% of the estimate of 167 x 10^6 t/year by
Turner and Rabalais (2004).”
Now from one source we have 170 x 10^6 tonne, another one of 161 x 10^6 tonne, and a third of 167 x 10^6 tonne. So let us use 170 x 10^6 t/year (its all science so I can pick the big number) and I am pretty sure it is metric ton 2200 lbs. Now I used 100 lbs per cubic foot because I actually weighed a cubic foot of dirt.
So
170 x 10^6 tons/year x 2200 lbs /ton = 3.74 x 10^11 lbs
3.74 x 10^11 lbs x 3 (before soil conservation measures by man) = 11.22 x 10^11 lbs /year
Elevation of United States 2500 ft
http://www.infoplease.com/ipa/A0001792.htmlUnited States size 3.795 x 10^6 sq miles
http://www.infoplease.com/ipa/A0108355.html3.795 x 10^6 sq miles x (5280 x 5280) sq ft /mile = 1.057 x 10^14 sq ft
1.057 x 10^14 sq ft x 2500 ft (elevation) = 2.64 x 10^17 cubic ft
Now to convert soil lbs to cubic feet. I will use my number 100 lbs / cu ft.
11.22 x 10^11 lbs /year / 100 lbs /cu ft = 11.22 x 10^9 cu ft / year
So if the United States is eroded by the Mississippi how long does it take.
2.64 x 10^17 cu ft / 11.22 x 10^9 cu ft /year = 23.5 x 10^6 years
But now I will be a turkey and say that all of the other rivers in the United States all add up to the same sediment discharge number of the Mississippi. So
2.64 x 10^17 cu ft / (2) x 11.22 x 10^9 cu ft / year = 11.75 x 10^6 years to erode the United States.
.