Analysis of Turbulent Flow Measurements in a Flume with Induced Upward Seepage - Experimental Methods in Hydraulic Research - page 166

Fig. 2 General scheme of the flume at the laboratory (dimensions in centimeters)

The experimental zone was 8 m long, 0.5 m width, and 1.0 m high. The first 2 m of
this experimental zone were used to stabilize the flow in order to address it into
subcritical regime to the region where the measurements were taken (Herrera-
Granados 2008a ). Figure 1 shows the flume and the tank that provoked upward
seepage. In order to allocate a 0.2-m porous bed (constituted by a sandy fine soil), a
special structure was built 0.30 m over the lowest part of the flume to protect the
small pipes at the bottom of the channel (Herrera-Granados 2008a ). These pipes
played an important role because the water from the external tank flowed through
them and provoked distributed hydraulic pressures acting on the lowest part of the
channel (Herrera-Granados 2008b ).
The small lines under the sandy layer (shown in Fig. 2 ) represent the pipes that
were connected to the external tank. The function of the tank was to feed with water
the 0.3 m region under the sandy layer in order to gain a constant hydraulic head
higher than the water level of the open-channel flow. The tank was provided with
three hoses, one flowmeter, and a small spillway to control the induced hydraulic
pressures provoking upward seepage through the porous sandy layer.
Figure 2 depicts the parts of the flume and the location of the velocimeter
P-EMS in three cross sections of the flume ( X

¼

1.0, 3.0, and 5.0 m, according to
the established reference frame, which is depicted in the same figure). The P-EMS
(with its accessory E-30) is able to measure the instantaneous velocities in two
directions ( x , y ) with an accuracy of 0.001 m/s. The turbulent flow measurements
were taken in 35 different points at each cross section. The general scheme of
the external tank, its main components and the representation of the inducted
hydraulic head ( DH ) as well as the view of the flume from the cross section A-A
(see Fig. 2 ) with its geometry and the locations of the above-mentioned measure-
ment points are depicted in Fig. 3 . A thin layer of geotextile was allocated in
between the sandy layer and the metal base that was symmetrically drilled to
allow upward flow.
The geotextile let the pressure and consequently the seepage flow to be dis-
tributed uniformly in the whole porous medium.