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We know the hydraulic head at the ground surface is equal to the elevation of the ponded water (0.8 m). We assume the pressure is atmospheric in the drain (that is, the water flowing to the drain discharges at the end of the drain without backing up water in the drain). Hydraulic head is the sum of pressure head in terms of a height of a column of water and elevation. Atmospheric pressure is used as the zero-reference point for quantifying pressure so, at the drain, the pressure is zero and the hydraulic head is equal to the elevation.

V. In case more point to be located say P, from vertical line QP at any distance x from F. With F as the centre and QH as the radius, draw an arc to cut vertical line through Q in point P. Also, the phreatic line is a flow line, and must start perpendicularly to the u/s face AB which is a 100% equipotential line. Too many flow channels to distract the attraction from the essential features. From the drawn flow net, Nf and Nd can be easily counted, and hence, the seepage discharge can be easily computed by using Eqn.

What if I encounter difficulties while drawing a Flow Net Diagram?

(13 minutes)A discussion of the material in this video is provided in Section 2.6 “The “Hear See Do” of Flow Nets” of the Groundwater Project book “Graphical Construction of Groundwater Flow Nets”. Section 2.6 can be read online, or the entire book can be read online or a PDF of the book can be downloaded. Mastering the art of flow net construction involves applying fundamental principles of hydraulics and soil properties.

Ultimately, the choice of method will depend on the specific requirements of the project and the expertise of the engineer or researcher. This can be done using the principles of hydraulics and the elevation of the water table. The geometric transformation from an anisotropic system to an isotropic system can be viewed as transforming the hydraulic conductivity ellipse into a circle.

Challenges and Limitations of Drawing Flow Nets

So, these locations are constant-head boundaries with a head of 10 m on the ground surface upgradient of the dam and a head of 6 meters on the downgradient side (Figure 6). The lateral portions of the aquifer are not bounded so they must be drawn far enough from the dam so that no significant leakage occurs between the reservoirs and the underlying sand at the distant ends of the system. The highest rate of seepage into the sand will be immediately up gradient of the dam with seepage decreasing with distance up gradient. If, after constructing a flow net, it appears that the diagram is not wide enough, it can be redrawn with greater lateral extent from the dam until an acceptable flow net is obtained.

• An important assumption for graphical construction of a flow net in a plan view is the absence of areally distributed recharge, such as infiltration of precipitation to the flow system.
• This is where this blog post comes in – we’ll take you by the hand and show you how to draw flow net diagrams in soil mechanics, step by step.
• Flow nets are a crucial tool in geotechnical engineering, particularly in the analysis of groundwater flow and seepage through soils.
• In this section, we will provide a step-by-step guide to drawing a flow net diagram using a graphical method.

Understanding flow nets is crucial for correctly designing and evaluating the performance of structures such as dams and retaining walls, ensuring efficient water management and stability. The intersection of a flow line and an equipotential line forms a streamline, which represents the direction of groundwater flow at a specific point. Flow nets are a powerful tool in foundation engineering, providing a visual representation of groundwater flow and seepage through soils. By understanding the fundamentals of flow nets, engineers can analyze and predict seepage behavior, optimize foundation design, and ensure the stability of dams and other hydraulic structures. As geotechnical engineering continues to evolve, the importance of flow nets will remain a crucial aspect of foundation engineering.

The flow net diagram offers several benefits in soil mechanics, including the ability to visualize complex flow patterns, determine the direction and magnitude of flow, and identify areas of seepage and saturation. By analyzing the flow net diagram, engineers can identify potential problems, such as erosion and settlement, and take corrective action to mitigate these issues. Additionally, the flow net diagram can be used to design more efficient and effective engineering projects, such as drainage systems and water supply systems. Furthermore, the flow net diagram can be used to predict the behavior of water in the soil under various conditions, such as changes in rainfall or groundwater levels. A flow net diagram is a two-dimensional representation of the flow of water through a soil mass. It consists of a series of curves, known as flow lines, and equipotential draw flow nets lines, which are lines of equal hydraulic head.

7 Flow Nets Provide Insight Into Groundwater Flow

If we extract a core sample from a porous medium along a given direction and measure the hydraulic conductivity along the longitudinal axis of the core, we obtain the directional hydraulic conductivity (Kd) in that direction. If hydraulic conductivity is isotropic, then Kd is the same in all directions. The direction in which Kd attains its maximum value is known as the maximum principal direction.

BOX 3 – Derivation: Formula for Volumetric Flow Rate Through a Flow Net

A flow net is a network of flow lines and equipotential lines that represent the path of water as it flows through a porous medium. Flow lines indicate the direction of water flow, while equipotential lines represent the hydraulic head or total energy of the water at a given point. The significance of flow nets lies in their ability to provide a visual representation of the complex flow patterns that occur in soils, allowing engineers to analyze and predict seepage behavior. A flow net diagram is a graphical representation of the flow of water through a soil mass. It’s a crucial tool in soil mechanics used to analyze seepage problems, such as the potential for erosion, piping, or instability in earth structures like dams, levees, and retaining walls. The diagram uses equipotential lines (lines of constant hydraulic head) and flow lines (representing the direction of water flow) to visualize the water movement patterns within the soil.

• Flow lines are drawn perpendicular to the equipotential lines, representing the path of water flow.
• A flow net diagram is a graphical representation of the flow of water through a soil or rock mass, showing the direction and magnitude of the flow.
• Figure Box 5-4 Only a small portion of the field with parallel drains needs to be drawn to develop a flow net.
• Flow net diagrams can be constructed using various methods, including graphical methods, numerical methods, and analytical methods.

A groundwater flow net is, in effect, a graphical solution of the groundwater flow equation. The procedure for constructing a graphical flow net does not accommodate boundaries with a defined flux other than zero. The rate of inflow can be determined if the value of hydraulic conductivity is known.

The Basics of Seepage

This is discussed in section 2.9 which addresses topographically driven flow. The ability to predict and visualize groundwater flow with flow nets is invaluable for the sustainable management of aquifers. Using flow nets, engineers can simulate different scenarios, such as high rainfall seasons or extended droughts, to assess the resilience and recharge capacity of an aquifer. This simulation capability informs strategies for water extraction and conservation that align with environmental and community needs. A flow net is a graphical representation of flow through porous media, characterized by equipotential and flow lines to simplify complex flow patterns.

Step 3: Draw the Flow Net Diagram

The first flow line KLM is formed by the flow of water on the upstream of the sheet pile, the downstream of the sheet pile and at the interface of the base of the dam and the soil surface. Anisotropy can occur in a horizontal flow net as well as in a vertical one. Anisotropy in the horizontal plane is generally the result of a directional fabric in the material such as fracture planes. However, the principal directions for flow in the plan view might not be as obvious as for flow in a vertical cross section (as above example). The principal directions in a vertical cross section are often (but not always) taken to be horizontal and vertical because many subsurface settings consist of horizontal layers. By contrast, the principal directions for flow in a plan view are generally not in east-west/north-south directions.

It is a curvilinear net formed by the combination of flowlines and equipotential lines. An earth dam is used as an example for discussion of drawing flow nets in an unconfined system as illustrated in Figure 13 and described in Box 4 which can be accessed from the caption of Figure 13. In contrast to the previous section, material at the ground surface is impermeable, and earth material is brought in from nearby to construct a dam, so in this case water flows through the dam instead of under the dam. The dam surface is sealed to prevent infiltration of water into the dam structure.