PART 1: The data below are the particle-size distributions, expressed as cumulative percentages, from samples of the A and B horizons collected from the Woodsmen's field and from the woods near the ropes course.

A Horizons
 

particle diameter  (mm)	WOODS (%)	WOODS (%)	WOODS (%)	FIELD (%)	FIELD (%)
3.36	24.0	9.6	28.2	7.1	16.7
1.0	36.0	16.7	40.9	12.7	21.3
0.71	41.0	34.4	43.9	16.6	24.1
0.6	44.0	37.7	45.2	18.9	26.7
0.5	45.1	42.1	47.0	22.1	32.3
0.335	53.4	48.7	50.9	29.5	38.2
0.25	60.0	55.1	54.8	36.7	42.5
0.18	65.0	59.7	58.4	45.5	48.4
0.125	69.4	65.0	63.4	57.0	58.2
0.09	74.0	69.5	68.3	66.9	64.0

B Horizons
 

particle diameter  (mm)	WOODS (%)	WOODS (%)	WOODS (%)	FIELD (%)	FIELD (%)
3.36	36.4	24.6	26.0	0.5	16.4
1.0	52.5	48.4	48.0	1.2	22.4
0.71	56.8	54.3	53.0	2.8	24.8
0.6	59.0	56.7	55.5	4.7	27.5
0.5	61.0	59.3	58.3	8.8	36.7
0.335	65.0	64.1	63.0	19.9	43.1
0.25	69.4	68.0	67.0	32.2	47.7
0.18	70.4	71.0	70.1	45.4	59.9
0.125	77.0	74.4	73.4	61.2	67.7
0.09	80.0	78.3	76.3	88.5	79.9

Choose one each of the soils from the woods and the field to be your representative soils.  Graph the soil textures, expressed as cumulative percentages, on soil gradation graph paper, or semilogarithmic paper with particle diameter on the logarithmic axis.
 
 

Remember that the settling rate for a sediment particle is given by Stokes’ Law.  Using 1.0 g/cubic cm for the density of water, 2.7 g/cubic cm for the density of the sediment, and 0.89 g/(cm sec) for the viscosity of water, calculate how much time would be required for the coarsest 40% of the A and B horizons for your chosen samples to settle out of a one-meter water column in a settling pond.  How much time would be required for 60% of these sediment to settle to the bottom of this same pond?

PART 2: Assume that the college has cleared a half-acre in each of the woods and the field for construction of some new buildings.  Although the sites are cleared in September, they both remain open and unstabilized, until May of the following year.  Using the Universal Soil Loss Equation and the information below, how much soil is lost from each site over this time?  (Assume the topsoil is removed and the exposed soil is in the B horizon)  How much soil would be eroded from these same sites over this period had they been evenly mulched with one ton of hay?  How much soil would be eroded from these same sites over this period had they been left in their existing conditions?  Express the sediment loss in both tons per acre and cubic yards (assume one ton = 0.87 cubic yards).

R = 90
K = 0.2 (A horizon); 0.28 (B horizon)
LS = 0.76
P = 0.9 for construction sites, 1.0 for undisturbed sites

Cover index factor (C):

no cover	C = 1.0
mulch at 0.5 tons per acre	C = 0.25
mulch at 1.0 tons per acre	C = 0.13
mulch at 1.5 tons per acre	C = 0.07
mulch at 2.0 tons per acre	C = 0.02
good cover of natural vegetation	C = 0.01

Rainfall Intensity Adjustment Factor for Estimating Monthly Portions of Soil Loss:

MONTH	percentage of annual R
January	3
February	3
March	4
April	5
May	6
June	12
July	13
August	18
September	18
October	8
November	8
December	7

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