Seepage of water through dams is quite common as almost all dams have some kind of seepage issue. This is due to the fact that reserved or retained water often seeps by the dam and its foundations.
Seepage of water through, around or under a dam is expected in all embankment dams and even in concrete dams. Thus, seepage monitoring becomes an essential performance indicator for all dams, embankment dams in particular.
The change observed in the seepage flows or their composition can be an essential indicator of the internal issues of the structure of the dam.
Seepage monitoring is quite critical for safety of dam, because over time, if not properly channeled, seepage can become a serious threat.
Need and Importance of Seepage Monitoring
While analyzing the structural behavior of a dam, the quantity of seepage, the seepage path, and the velocity of seepage water are vital.
Need for Monitoring Quantity of Seepage
A huge quantity of seepage around, under, and through the dam can result in the dissolution of either the chemical constituents of the rock or soil material present at the locations. We have several dams that are founded on evaporites such as gypsum that can get affected by it. This can enlarge the path for seepage which in turn can cause bigger dissolution. The larger the dam is, the greater chances of dissolution are there.
When a large amount of water moves around or under a dam, then both soil and rocks become saturated in the seepage areas. It also results in excessive hydrostatic uplift pressure which weakens and softens the soil and rocks.
The storage capacity of the reservoir becomes compromised when an excessive amount of seepage happens.
Importance of the Seepage Location
Locating the seepage becomes vital as there can be a case where the seepage is in a discrete and remote area. The seepage velocity can be high, which can cause erosion of particles of soil. This will result in piping-type failure of the dam.
A high quantity of seepage in a few concentrated paths can cause concentrated dissolution in that area.
Importance of Velocity of Movement
The occurrence of the piping failure will be more likely if the large particles are moved. This will only happen if the seepage velocity/water flow is high. The larger the velocity, the greater are the chances of erosion in the seepage path.
How to Monitor Seepage in Dams
The quantity of seepage entering in a seepage collection system is generally directly related to the level of the water in the reservoir. There are various methods to measure the seepage in dams.
Method 1: Calibrated Catch Container
This method is primarily for low quantity seepage. It is one of the simplest methods to monitor the rate and flow of seepage. The drain water should be connected in either of the two ways.
The first way is that the drain water is directed through a pipe with an open end. In the latter, the drain water is directed through a constructed channel with an overhang and a vertical drop. The calibrated catch container is then placed in position to catch the water and the time required to do so is measured with a stop watch. The catch container should preferably be made of stainless steel or some suitable plastic material which does not corrode easily.
Method 2: Flow Meter
The seepage water is collected in drain trench or toe drain, is discharged into the downstream of the dam via an open channel/pipe. In such a case, quanitity of flow is determined by measuring the velocity of water. The thought leader, Encardio-Rite, provides ultrasonic flow meters for monitoring the water flow/seepage ...[continue reading]
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