|
Gaugings. Gaugings of circulating
volumes. The gauging of a water obstacle is the measurement of the
circulating volume that happens through a in a while certain section: Q = v? S,
where v is the speed of the current and S is the section that is crossed by the
current. The different methods to calculate the gauging are: - Gauging by
measurement of speeds (windlasses); - Gauging by measurement of the water level;
- Gauging in a control section; - Gauging by tracers;
GAUGING BY SPEED MEASUREMENT. The main problem that considers in the gauging
is the difference of speeds between the different points from the section. This
method demands the measurement of the speed by means of denominated apparatuses
windlasses, constituted by a helix or vane that turns based on the speed of the
water. The linear rate of the water is then based on the number of returns
divided by the time, quotient that is moderate by means of a device electronic
accountant. The equation that relates the number of returns to the speed is v =
a?n + b, where to and b they are constant of the apparatus and n is nº of
returns started off by the time. The total section of a channel is divided in
small sections and from each one of them one is obtained I saw, so that Q = VI?
Si.
GAUGING BY MEASUREMENT OF THE WATER LEVEL. In a certain section the
circulating volume is function of the height of the lamina, is to say to Q = Q(h),
denominated function curved of capacity. If this curve is known and the height
of the water is moderate, the volume can be calculated immediately. This
measurement of the height becomes by means of a graduated sight call limnímetro.
The measures made by this method are cheap, but its main problem is the
existence of errors by change in the conditions of the section, either by
variation of the section, or by variation of the roughest, or del own regime del
river. This demands tared and a periodic control of the curves of capacity,
together with measures to guarantee the stability of the section avoiding
erosions, sedimentations and changes of roughest.
GAUGINGS IN A CONTROL SECTION. In points where the volume is not very high
they can make factory works that generate a section where the volume is
calculable by means of formulation. For example, in a garbage dump of thin wall
the volume comes dice by Q = Ca?2/3?(2?g?L)1/2?H3/2, that with coefficient of
contraction Ca "0.60 Q has left = 1,8?L?H3/2. Notice that H must be measured in
the zone that does not consider the contraction of the lamina by speed.
GAUGING BY TRACERS. The detectable, colorant substance injection of or
radioactive substance is based on that is measured waters under the injection
point. 2 methods exist:
CONTINUOUS METHOD OF INJECTION. In a certain section 1 of the hydraulic
current, a tracer with volume injects itself q1 and concentration c1, and the
concentration is moderate in 2 section c2 of the tracer taking care of who this
concentration reaches a stable value. Of this form it is that Q = (q1?c1)/c2.
The precautions that are precise to adopt are: a) The tracer does not have of
being destroyed nor being retained between the two sections. b) The
concentration c2 must be uniform and stable. c) The distance between the two
sections must be sufficient so that uniformice the tracer and not very long to
save tracers. The main problem with this method is the great amount of tracer
necessary to stabilize the concentration c2.
METHOD OF PRECISE INJECTION. It consists of injecting in the section a 1
well-known mass M of tracer and measuring in 2 the concentration of the tracer
based on the time, so that Q = M/"c?dt. This method has the advantage to save
tracer but it demands the continuous measurement of the concentration in section
2. The characteristics that the tracers must fulfill are: - To be unalterable
during the period of measures. - Not to be neither toxic nor polluting for the
people and the medium ambient. - To be soluble or miscible in water. - Easy to
measure as far as its concentration. - To be cheap. Within the used chemical
tracers more of they find the Sodium Chloride, the Sodium Dichromate and
Rodamina B. Within the radioactive tracers they emphasize Sodium 24, Phosphorus
32, 51 Chromium and Bromine 82.
WATER GAUGE STATIONS. The measurement of the volumes of makes of systematic
form in water gauge stations that is located in the main rivers. In Spain they
exist of the order of 500 stations controlled by the Water Police station, which
is a department that depends on the Hydrographic Confederations. The level
gauges are in charge to measure the volumes in certain points and of the
maintenance of these water gauge stations. |
