HIDROMETRI

Summary

This video script discusses surface flow in hydrology, specifically focusing on hydrometry, river types, surface runoff, basin shape influences, and triangular hydrographs. The first section covers hydrometry, explaining the methods used to measure stream flow, including velocity and cross-sectional area, with techniques such as the Chezy and Manning formulas, as well as direct measurements. It also explores various structures like weirs and flumes used to measure flow. The script concludes by addressing how flow speed is measured using devices like floats and electromagnetic sensors, and it touches on the importance of accurate flow data for hydrological studies.

Takeaways

• 😀 Hydrometry is the study of measuring water flow, particularly discharge in rivers and streams.
• 😀 Discharge measurement involves determining both the cross-sectional area and flow velocity at a specific measurement point.
• 😀 Common methods for measuring discharge include using formulas (Chezy, Manning, and Darcy-Weisbach), or physical structures like weirs and flumes.
• 😀 The Chezy formula calculates discharge by using a coefficient (C) that relates the flow velocity to the hydraulic radius.
• 😀 Manning's formula uses a different coefficient (n), and is used to estimate discharge in open channels like rivers.
• 😀 Three types of weirs used for discharge measurement include broad-crested weirs, sharp-crested weirs, and Cipolletti weirs.
• 😀 A flume is another structure used to measure discharge, where the water height and velocity are used to determine the flow rate.
• 😀 Flow velocity measurement can be done manually using floats or automatically with instruments like the electromagnetic flow meter.
• 😀 Manual measurement of water levels can be done using a staff gauge or automatic water level recorders (AWLR), which continuously record water height changes.
• 😀 Velocity profiling in rivers involves measuring the velocity at various depths and cross-sections of the river to estimate total discharge.
• 😀 The velocity of flow is measured at different depths (0.2, 0.6, and 0.8 of the total depth) using devices like current meters, to calculate the average flow velocity across the section.

Q & A

What is hydrometry and why is it important in surface water flow studies?

Hydrometry is the science of measuring the flow of water in rivers or channels. It is crucial because it helps determine the discharge, velocity, and water surface elevation, which are essential for understanding the behavior of rivers and managing water resources.

What are the two main measurements taken during flow measurement?

The two main measurements are the cross-sectional area of the river or channel (referred to as 'A') and the velocity of the flow at the measurement point (referred to as 'V').

How is flow discharge calculated?

Flow discharge (Q) is calculated using the formula Q = V * A, where 'V' is the flow velocity and 'A' is the cross-sectional area of the flow. This can be calculated for each section of the river or channel.

What is the significance of the Chezy, Manning, and Strickler formulas in hydrometry?

These formulas are used to estimate the flow velocity ('V') at a measurement point. They differ in the coefficients they use, with the Chezy formula using the Chezy coefficient (C), the Manning formula using the Manning coefficient (n), and the Strickler formula using a similar approach with different parameters.

What are the types of weirs discussed in the transcript, and how do they differ?

The types of weirs discussed are broad-crested weirs, sharp-crested weirs, and Cipolletti weirs. A broad-crested weir has a long flat crest, while a sharp-crested weir has a thin crest without length. The Cipolletti weir combines both width and height, providing a specific flow measurement design.

What is the role of a flume in flow measurement?

A flume is a structure used to measure flow by observing changes in water height and the width of the channel. It is often used to detect variations in water level due to changes in flow conditions.

How is the water surface elevation measured in hydrometry?

Water surface elevation can be measured manually using tools like staff gauges or automatically with water level recorders that continuously track water height and display the data on a graph.

What are the methods used for measuring flow velocity in a river or channel?

Flow velocity can be measured using methods such as floats, acoustic sensors, and mechanical devices like the 'M' type instruments. These devices help calculate the velocity of the flow at various depths across the channel.

What is the significance of the different depths (0.2H, 0.6H, 0.8H) used in velocity measurement?

The different depths (0.2H, 0.6H, 0.8H) are used to obtain a more accurate measurement of velocity across the cross-section of the flow. These depths represent positions at various heights in the water column to calculate average velocity more effectively.

What are the two methods for calculating discharge in a river channel mentioned in the transcript?

The two methods for calculating discharge are the Midsection Method and the Charamin Section Method. These methods help estimate the flow by calculating the discharge per unit width and adjusting for variations in the cross-sectional profile.