Suspendedsediment Samplers.
Suspendedsediment samplers can be classified as (1) depthintegrating, (2) pointintegrating, (3) singlestage, or (4) pumping samplers.
Depthintegrating samplers accumulate a watersediment sample in a pintsize milk bottle as they are lowered to the stream bed and raised back to the surface at a uniform rate of transit.
They are designed so that the velocity in the intake nozzle is nearly equal to the local stream velocity.
Samples may be collected by wading in a stream, by hand from a suitable support, or mechanically with a cableandreel setup.
The U.S. DH48 sampler (4.5 lb) (Fig. 1518) with wadingrod suspension is used in shallow streams when the product of flow depth (in feet) and mean velocity (in feet per second) does not exceed 10 [22].
The U.S. DH59 sampler (24 lb) with handline suspension is used in streams with low velocities but with depths that do not permit samples to be collected by wading.
The U.S. D49 sampler (62 lb) with cableandreel suspension is designed for use in streams beyond the range of handoperated equipment.
Depthintegrating samplers were developed to improve sampling accuracy and to reduce the cost of collecting suspendedsediment data.
Pointintegrating samplers accumulate a watersediment sample that is representative of the mean concentration at any selected point in a stream during a short interval of time.
The intake and exhaust characteristics of pointintegrating samplers are identical to those of depthintegrating samplers.
A rotary valve that opens and closes the sampler is operated by a solenoid energized by batteries at the surface.
The current flows to the solenoid by a currentmeter cable, which suspends the sampler.
Pointintegrating samplers can be used to collect depthintegrating samples by leaving the valve open as the sampler is moved through the stream vertical.
This permits depthintegration in streams that are too deep to be appropriately sampled with a depthintegrating sampler.
The U.S. P46 and P61 (100 lb), P63 (200 lb), and P50 (300 lb) pointintegrating samplers are in current use.
The singlestage sampler was developed to obtain suspended sediment data in flashy streams, particularly those in remote areas [24].
It is used to sample sediment at a specific depth and on the rising stage only.
The sampler operates on the siphon principle, and therefore the velocity in the intake is not equal to the stream velocity.
With careful operation, the singlestage sampler can be used to obtain supplemental data on suspendedsediment concentration at selected points.
The pumping sampler does not require an operator and is designed to obtain a continuous record of sediment concentration by sampling at a fixed point at specific time intervals.
The velocity in the intake is not equal to the stream velocity, and the intake does not meet the requirements of an ideal sampler, since it does not point into the flow.
However, the pumping sampler can be calibrated by rating its measurements against those obtained with standard depthintegrating or pointintegrating samplers.
Bedload Samplers.
Bedload samplers are of three types: (1) basket type, (2) pan type, and (3) pressuredifference type.
The basket and pan types cause an increase in resistance to flow and a reduction in stream velocity at the sampling location.
The reduction in stream velocity interferes with the rate of bedload transport, compromising the accuracy of the measurement.
The pressuredifference bedload sampler is designed to eliminate the reduction in velocity, resulting in increased sampling accuracy.
The efficiency of a bedload sampler, i.e., the ratio of sampled bed load to that
actually transported, varies with sample type, method of support. particle size, and bed configuration.
Calibration of bedload samplers has indicated a mean efficiencyof about 4S percent for the basket and pan types and 70 percent for the pressuredifference type.
Bedmaterial Samplers
Bedmaterial samplers are of three types: (1) drag bucket, (2) grab bucket, and (3) verticalpipe, or core sampler.
The dragbucket samá pier consists of a weighted section of cylinder with an open mouth and cutting edge.
As the sampler is dragged upstream along the bed, it collects a sample from the top layer of bed material.
The grabbucket sampler is similar to the dragbucket, consisting of a cylinder section attached to a rod, and used primarily in shallow streams.
The verticalpipe, or core sampler, consists of a piece of metal or plastic pipe that can be forced into the stream by hand.
Generally, the dragbucket and grabbucket samplers do not obtain representative samples of bed material because of the loss of fine material.
The core sampler is satisfactory for use in shallow streams.
The U.S. BMH53 sampler consists of a 9in.long, 2in.diameter brass or stainless steel pipe with a cutting edge and suction piston attached to a control rod.
The piston is retracted as the cutting cylinder is forced into the stream bed.
The partial vacuum that develops in the sampling chamber as the piston is withdrawn assists in holding the sample in the cylinder.
The sampler can be used only in streams shallow enough to be waded.
The U.S. BMH60 bed material sampler with both handline and cable suspension is designed to scoop up a sample of bed sediment about 3 in. wide and 2 in. deep.
At the close of the sampling operation, the cutting edge rests against a rubber stop. which prevents any sediment from being lost.
The aluminum sampler weighs 30 lb and the brass sampler, 40 lb.
It is used to collect bedmaterialsediment samples in streams with low velocities but with depths beyond the range of the BMH53 sampler.
The U.S. BM54 bedmaterial sampler (100 lb) with cable suspension is similar in design to the BHM 60 sampler.
It is used in deep streams where a heavier sampler is necessary.
Suspendedsediment Discharge Measurements
Suspendedsediment samplers are used to determine sediment concentration at a point in a stream (i.e., a stream vertical), except for a small unmeasured zone located just above the stream bed.
With wading equipment, measurements can generally be made down to within 0.3 ft of the stream bed.
For cablesupported equipment, the unmeasured zone varies between 0.5 and 1.0 ft, depending on the size of sampler used.
Suspendedsediment discharge measurements include: (1) suspendedsediment concentration, (2) particle size, (3) specific gravity, (4) temperature of watersediment mixture, (5) water discharge, and (6) distribution of flow in the stream cross section.
The streamflow depth and velocity and the facilities at the sampling site (bridge, cableway, and so on) have an influence on the choice of sampler.
Stream depth determines whether hand samplers, such as the DRA8 or DR59, or a cablesuspended sampler, such as the D49, should be used.
Flow depths over 15 ft require the use of pointintegrating samplers to avoid overfilling of the sampling bottles.
The larger the product of flow depth times mean velocity, the heavier the sample required for proper measurement.
The number of sampling verticals depends on the desired accuracy and the variation of sediment concentration across the stream.
For streams with a stable cross section and essentially uniform sediment concentration across the width, sampling at a single vertical is usually adequate.
Depthintegrating samplers produce a suspendedsediment concentration, which can be measured in parts per million and converted to milligrams per liter.
The suspendedsediment discharge is given by the following formula:
Q_{s} = 0.0027C_{s}Q
(1526)
in which Q_{s} = suspended sediment discharge in tons per day; C_{s} = suspendedsediment concentration in milligrams per liter; Q = water discharge in cubic feet per second, and 0.0027 is the conversion factor for the indicated units.
Table 158 shows a factor to convert concentration in parts per million to milligrams per liter.
There are two techniques to measure suspendedsediment discharge: (1) EDI, or equaldischarge increments, and (2) ETR, or equaltransit rate.
In the EDI method, sampling is done at the centroids of equaldischarge increments.
In the ETR method, sampling is done at the centroids of equallength increments.
The EDI method requires a knowledge of the lateral distribution of streamflow prior to the selection of sampling verticals.
The ETR method is applicable to shallow streams where the cross sectional distribution of streamflow is not stable.
Generally, the EDI method requires fewer sampling verticals than the ETR method.
The ETR method, however, does not require a prior discharge measurement.
The suspendedsediment concentration in the EDI method is the average obtained from several depthintegrating samples.
In the ETR method, the suspended sediment concentration is that of a composite sample encompassing several depthintegrating samples.
The error in suspendedsediment discharge provided by the measurement varies with the depth of the unsampled zone and the size distribution of suspended load.
The error tends to be smallest in the cases where the vertical concentration gradient in the unsampled zone is small.
The concentration gradient near the bed is small for silt and clay particles and large for coarser sand particles.
Corrections in sampled suspendedsediment discharge to account for the unsampled portion are usually obtained through appropriate sediment transport predictors such as the Colby 1957 method or the modified Einstein procedure [7, 9].
QUESTIONS

Give two alternate definitions of particle sphericity.

What is the difference between specific weight and specific gravity?

What is standard fall velocity? What is standard fall diameter?

What is the difference between sediment production and sediment yield?

Describe the differences between normal and accelerated erosion.

Name four sources of sediment.

What is the rainfall factor R in the Universal Soil Loss Equation?

What is sedimentá delivery ratio?

Why is sedimentdelivery ratio inversely related to drainagebasin area?

Why are two formulas needed in the Dendy and Bolton approach to the computation of sediment yield?

Describe the classifications of sediment load based on (1) predominant mode of transport and (2) whether the particle sizes are represented on the channel bed.

What are possible forms of bed roughness in alluvia! channels?

What is range of applicability of the MeyerPeter formula for bedload transport?

What is the basic difference between the Colby 1957 and Colby 1964 procedures for the computation of discharge of sands?

What is a sediment rating curve?

What is sediment routing?

What is the trap efficiency of a reservoir?
 What is a debris basin?

Describe two techniques to measure suspendedsediment discharge.
How do they differ in the evaluation of suspendedsediment concentration?
PROBLEMS

Calculate the fall velocity of a sediment particle using Stokes' law.
Assume a diameter mm, kinematic viscosity 1 centistoke, specific gravity 2.65.

Calculate the specific weight of a sediment deposit in a reservoir, after an elapsed time of 100 y, under moderate drawdown conditions.
Assume the following mix of particle sizes: sand 55%, silt 30%, clay 15%.

Compute the average annual soil loss by the universal soil loss equation for a 300ac watershed near Lexington, Kentucky, with the following conditions: (1) cropland, 250 ac, contoured, soil is Keen silt loam, slopes are 7% and 150 ft long, C = 0.15; (2) pasture, 50 acres, 75% canopy cover, 60% ground cover with grass, soil is Ida silt loam, slopes are 10% and 200 ft long.

Compute the average annual soil loss by the universal soil loss equation for a 1mi2 forested watershed near Bangor, Maine.
The soil is Fayette silt loam, the slopes are 3% and 300 ft long, and the site is 80% covered by forest litter.

Using the Dendy and Bolton formula, calculate the sediment yield for a 25.9km^{2} watershed with 5 cm of mean annual runoff.

Determine whether a particle of 2mm diameter is at rest under a 3m flow depth and 0.0002 channel slope.
Assume a specific gravity 2.65 and kinematic viscosity 1 centistoke.

Determine the form of bed roughness that is likely to prevail under the following flow conditions: mean velocity 3 ft / s, flow depth 8 ft, channel slope 0.0002, and mean particle diameter 0.3 mm.

Given the following flow characteristics: flow depth 9 ft. mean velocity 3 ft l s, channel slope 0.00015, mean particle diameter 0.4 mm, mean channel width 250 ft. Calculate the bed material transport rate by the Duboys formula.

Given the following flow characteristics: flow depth 3 ft, mean velocity 5 ft / s, energy slope 0.009, mean particle diameter 1.0 in., mean channel width 30 ft.
Calculate the bedámaterial transport rate (in tons per day) by the MeyerPeter formula.

Given the following flow characteristics: flow depth 5 ft, mean velocity 4 ft / s, mean channel width 180 ft, measured concentration of suspended bedmaterialdischarge 200 ppm.
Calculate the total bedmaterial discharge (in tons per day) by the Colby 1957 method.

Given the following flow characteristics: flow depth 5 ft, mean velocity 3 ft / s, median bed material size 0.3 mm, mean channel width 225 ft, water temperature 70°F, wash load concentration 300 ppm.
Calculate the discharge of sands by the Colby 1964 method.

A reservoir is to be built with a total storage capacity of 50 hm^{3}.
The contributing drainage basin is 800 km^{2}, and the mean annual runoff at the site is 200 mm.
Assume wellgraded sediment deposits with average specific weight 1400 kg/ m^{3}.
(a) How long will it take for the reservoir to lose 20% of its storage volume?
(b) How long will it take for the reservoir to fill up with sediment?
Estimate sediment yield by the Dendy and Bolton formula.

A reservoir is to be built with a total storage capacity of 120 hm^{3}.
The contributing drainage basin is 425 km^{2}, and the mean annual runoff at the site is 45 mm.
Assume coarse sediment deposits with average specific weight 13 kN/ m^{3}
(a) How long will it take for the reservoir to lose 80% of its storage volume?
(b) How long will it take for the reservoir to fill up with sediment?
Estimate sediment yield by the Dendy and Bolton formula.

Derive the conversion factor 0.0027 in Eq. 1526.

Calculate the suspendedsediment discharge (in tons per day) for the following cases: (1) suspended sediment concentration 100 ppm, water discharge 1200 ft^{3} / s, and (2) suspended sediment concentration 80,000 ppm. and water discharge 5000 ft^{3} / s.

Derive the unit conversion factor C in the following formula: Q_{s} = CC_{s}Q, in which Q_{s} is given in kilonewtons per day, C_{s} in milligrams per liter, and Q in cubic meters per second.

Calculate the suspendedsediment discharge (in kilonewtons per day) for a suspendedsediment concentration of 150 ppm and a flow of 68 m^{3}/s.

Calculate the suspendedsediment discharge (in kilonewtons per day) for a suspendedsediment concentration of 22,000 ppm and a flow of 155 m^{3}/ s.
REFERENCES
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13. Dendy, F. E. , and G. C. Bolton. (1976). "Sediment YieldRunoffDrainage Area Relationships in the United States," Journal of Soil and Water Conservation. Vol. 31, No.6, November December, pp. 264266.
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36. Rouse, H. (1939). "An Analysis of Sediment Transportation in the Light of Fluid Turbulence," USDA Soil Conservation Service, Report No. SCSTP2S, Washington, D.C.
37. Simons, D. B. , and E. V. Richardson. (1966). "Resistance to Flow in Alluvial Channels," U.S. Geological Survey, Professional Paper No. 422J, Washington, D.C.
38. Simons, D. B., and F. Senturk. (1976). Sediment Transport Technology. Fort Collins, Colorado: Water Resources Publications.
39. Toffaleti, F. B. (1969). "Definitive Computation of Sand Discharge in Rivers," Journal of the Hydraulics Division. ASCE, Vol. 95, No. HY1, Jan., pp. 225248.
40. U.S. Army Corps of Engineers. (1987). "Sedimentation Investigations in Rivers and Reservoirs," Engineer Manual EM 111024000, Office of the Chief of Engineers, Washington, D.C., Draft.
41. USDA Soil Conservation Service. (1983). National Engineering Handbook. Section 3, Sedimentation, 2d. ed.
42. Williams, J. R. (1975). "Sediment Yield Prediction with the Universal Soil Loss Equation Using RunoffEnergy Factor," in Present and Prospective Technology f or Predicting Sediment Sources and Sediment Yields . .. USDA Agricultural Research Service, Publication ARSS40.
43. Wischmeier, W. H., and D. D. Smith. (1965). "Predicting RainfallErosion Losses from Cropland East of the Rocky Mountains," USDA Agricultural Research Service. Agriculture Handbook No. 282 . May.
44. Wischmeier, W. H., C. B. Johnson , and B. V. Cross. (1971). "A Soil Erodibility Nomograph for Farmland and Construction Sites," Journal of Soil and Water Conservation. Vol. 26, No.5, Sept.áOct.
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SUGGESTED READINGS
American Society of Civil Engineers. (1975). Sedimentation Engineering. Manual No. 54.
Colby, B. R. (1964). "Discharge of Sands and Mean Velocity Relations in SandBed Streams," U.S. Geological Survey Professional Paper 462A. Washington, D.C.
Guy, H. P. (1970). "Fluvial Sediment Concepts," U.S. Geological Survey, Techniquesfor Water Resources Investigations. Book 3, Chapter Cl. 1970.
Simons, D. B., and F. Senturk. (1976). Sediment Transport Technology. Fort Collins, Colorado: Water Resources Publications.
U.S. Army Corps of Engineers. (1987). "Sedimentation Investigations in Rivers and Reservoirs," Engineer Manual EM 111024000, Office of the Chief of Engineers, Washington, D.C., Draft.
USDA Soil Conservation Service. (1983). National Engineering Handbook. Section 3, Sedimentation, 2d. ed.