The SedErode Measurement System

The SedErode Measurement System

Background

SedErode (Figure 7) is a

field instrument for measur-

ing the erodability of cohe-

sive-based sediment in its

natural environment. Sed-

Erode applies a known hydro-

dynamic force (shear stress)

to the sediment surface while

monitoring the response of

the sediment in terms of sedi-

ment release (concentration),

from which the critical ero-

sion shear stress can be deter-

mined. This parameter (shear

stress) is a key factor when

considering sediment trans-

port problems and engineer-

ing design. The results are used to successfully predict the erosion behav-

ior of natural sediments and to establish a relationship between erosion

shear stress and density. This instrument was developed and is used by

HR Wallingford, of Wallingford, England.

Technology

The SedErode unit, consisting of a head unit and control box, is portable

and self-contained. The head unit consists of a 40-cm-diam circular base

plate. The base plate has a short, thin wall tube underneath, and a pump

and chamber mounted on top containing a reservoir, flow diffuser, and

pump connections. The chamber is also fitted with filling and venting

ports. To use, the thin wall tube is pressed into the sediment until the

base plate rests on the surface. The pump is started and water is recircu-

lated slowly over the surface of the sediment. The flow rate of the pump

is gradually increased until the turbidity starts to increase. The shear

stress can then be read directly or test results can be logged to produce the

erosion characteristics of the sediment. Outputs from SedErode include

the shear stress and the turbidity associated with the stress.

Applications of the SedErode include sedimentation studies, real input

for modeling and design, monitoring of sediment features, and environ-

mental assessment. The system is suitable for intertidal mudflats and

coastal fringes, rivers, lakes, reservoirs, sewers and urban drainage systems,

disposal ground on land and at sea, dredging and reclamation of any

muddy-based sediment. The system currently operates in the dry, with

optimized results obtained from intertidal areas during low tides. To

determine submerged marine sediment characteristics, the sediment must

be brought to the surface and placed on a special sampling plate designed

for the SedErode system.