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Water and Sediment Sampler for Plot and Field Studies¹

ABSTRACT

The design and performance characteristics of a flush-type sampling device for plot and field studies are described. The sampler is weld-constructed and requires excavation and water conveyance for installation. It operates with no external power supply and collects consistently a known fraction of water and sediment passing through it. In laboratory tests, the sampler collected 2.65% (number of data points [n] = 54, standard deviation [s] = 0.0040) of all water passing through it at average flow rates ranging from 18 to 196 L min^–1. Sample volumes ranged from 0.75 to 18.7 L. Correlation analysis showed that sampling percentage was independent of flow rate (n = 40, correlation coefficient = r = –0.04) over the range tested, in other laboratory tests, 30 sampling runs with inflow rates and total sediment concentrations ranging from 35 to 182 L min^–1 and 252 to 1410 mg L^–1, respectively, showed that the ratios of waste to sample sediment concentrations were approximately one for total sediment (1.001), and for the sand (1.097), silt (1.008), and clay (1.020) fractions. Sand and clay ratios were shown to be statistically independent of total sediment concentration, but silt (r = 0.30, n = 30) and total sediment (r = 0.44, n = 30) ratios increased slightly with increasing total concentration. Monte Carlo simulation was performed to illustrate the suitability of the flush-sampler for field and plot runoff studies. Simulation results indicated that for runoff estimates measurement error would exceed 10% with 33% probability for triplicate plots, but with only 16% probability in five plot studies. Additional simulation considering only measurement error associated with the sampler shows that the minimum number of paired samples required to detect sediment loss reductions of 50, 25, and 10% is 3, 4, and 16, respectively.

Key Words: error analysis • Monte Carlo simulation • proportional sampler • run off • sampling error

¹ Pap. no. 10091 of the Journal Series of the North Carolina Agric. Res. Service, Raleigh, NC 27695-7601.

² Extension Specialist, now at Water Office, USEPA, Washington, DC; Extension Specialist; Former Extension Specialist, now Agricultural Engineer, USDA-SCS, Athens, OH 45701; Extension Specialist, and Professor, respectively, Biological and Agricultural Engineering, North Carolina State Univ., Raleigh, NC 27695-7625.

Received for publication November 18, 1985.