Contenido

El transporte sólido de un curso de agua, al tener características tan variadas, exige también una gama variada de procedimientos para su determinación, involucrando instrumentos específicos para cada caso. A continuación se describen algunos de estos dispositivos y procedimientos.

Determination of solid transport in suspension

The solid material in suspension in a stream, whether it comes from a saltation process, or is transported in suspension over a longer distance, is greatly influenced by the velocity and turbulence of the medium that transports it. For this reason, the device intended to capture the sample to be analyzed must alter the point where the sample is taken as little as possible. Some of these devices are: the so-called Delft bottle;[2]​ the US BM 54 sampler,[3]​[4]​ or the USP-61.[5]​.

There are two procedures to carry out these solid transport measurements, applicable depending on the specific purpose for which the measurement is carried out:

The first is an instantaneous measurement. In this case, a water sample is captured at a certain point in the flow section by means of a device that is removed for analysis in the laboratory.

And the second, which could be called integrative. The procedure consists of sucking in a certain amount of water using a small pump, containing the solid material transported in suspension, for a certain time. By measuring in the laboratory the solid material captured (in grams) and the volume of water pumped (in liters), the solid transport is determined expressed in g/liter, as:.

Determination of solid transport by bottom trawl

The material that we find at the bottom of the bed of a watercourse can basically have two origins: it can be formed by the thick material that the current has not managed to displace, or it can be formed by materials dragged during some flood events.

The study of bottom transport is more complex than the study of material transported in suspension.

Bottom solid transport, in gravel-bed water courses, has been described by some researchers,[6][7]​ as a phenomenon that can be decomposed into different phases, in particular with two conditions of sediment movement. Once the critical state of the beginning of the movement has been overcome, in a first phase, sediment transport manifests itself with a moderate intensity next to a certain threshold of liquid flow, while, in the second phase, the intensity of bottom drag increases. The threshold of the liquid flow that defines the limit between the two phases of solid transport would correspond to the flow of a full channel,[8][9]​ even though the beginning of the second phase is associated[7]​ with the rupture of the bed armor and is related to a flow rate equal to 80% of that corresponding to the full channel.[10]​ The intensity of transport, much greater in the second phase, occurs only during short time intervals, especially in small watercourses with gravel beds and high slope, so most of the annual sediment production would occur during the first phase.[11]​[12]​.

To obtain samples of solid bottom transport, several types of samplers can be used, among which we can remember the BTMA (Bed Transport Meter Arnhem) type, the Helley Smith sampler,[13]​ USBL-84, the Delft Nile sampler (DNS) and the KAOLYI drag sampler,[2]​ among others.

In small and medium-sized watercourses, sediment traps similar to those shown in the figure can be built. This procedure is the most appropriate whenever possible, reaching levels of precision very close to 100%. However, it is difficult to apply in large watercourses.

Contenido

El transporte sólido de un curso de agua, al tener características tan variadas, exige también una gama variada de procedimientos para su determinación, involucrando instrumentos específicos para cada caso. A continuación se describen algunos de estos dispositivos y procedimientos.

Determination of solid transport in suspension

The solid material in suspension in a stream, whether it comes from a saltation process, or is transported in suspension over a longer distance, is greatly influenced by the velocity and turbulence of the medium that transports it. For this reason, the device intended to capture the sample to be analyzed must alter the point where the sample is taken as little as possible. Some of these devices are: the so-called Delft bottle;[2]​ the US BM 54 sampler,[3]​[4]​ or the USP-61.[5]​.

There are two procedures to carry out these solid transport measurements, applicable depending on the specific purpose for which the measurement is carried out:

The first is an instantaneous measurement. In this case, a water sample is captured at a certain point in the flow section by means of a device that is removed for analysis in the laboratory.

And the second, which could be called integrative. The procedure consists of sucking in a certain amount of water using a small pump, containing the solid material transported in suspension, for a certain time. By measuring in the laboratory the solid material captured (in grams) and the volume of water pumped (in liters), the solid transport is determined expressed in g/liter, as:.

Determination of solid transport by bottom trawl

The material that we find at the bottom of the bed of a watercourse can basically have two origins: it can be formed by the thick material that the current has not managed to displace, or it can be formed by materials dragged during some flood events.

The study of bottom transport is more complex than the study of material transported in suspension.

Bottom solid transport, in gravel-bed water courses, has been described by some researchers,[6][7]​ as a phenomenon that can be decomposed into different phases, in particular with two conditions of sediment movement. Once the critical state of the beginning of the movement has been overcome, in a first phase, sediment transport manifests itself with a moderate intensity next to a certain threshold of liquid flow, while, in the second phase, the intensity of bottom drag increases. The threshold of the liquid flow that defines the limit between the two phases of solid transport would correspond to the flow of a full channel,[8][9]​ even though the beginning of the second phase is associated[7]​ with the rupture of the bed armor and is related to a flow rate equal to 80% of that corresponding to the full channel.[10]​ The intensity of transport, much greater in the second phase, occurs only during short time intervals, especially in small watercourses with gravel beds and high slope, so most of the annual sediment production would occur during the first phase.[11]​[12]​.

To obtain samples of solid bottom transport, several types of samplers can be used, among which we can remember the BTMA (Bed Transport Meter Arnhem) type, the Helley Smith sampler,[13]​ USBL-84, the Delft Nile sampler (DNS) and the KAOLYI drag sampler,[2]​ among others.

In small and medium-sized watercourses, sediment traps similar to those shown in the figure can be built. This procedure is the most appropriate whenever possible, reaching levels of precision very close to 100%. However, it is difficult to apply in large watercourses.