Infiltrasi dan Perkolasi

Summary

This lecture on hydrology covers key concepts such as infiltration and percolation. Infiltration refers to the flow of water into the soil, while percolation involves the downward movement toward groundwater. The capacity of soil to absorb water, known as infiltration capacity (FP), is influenced by various factors including soil type, moisture content, and surface conditions. The lecture explains how FP is measured using tools like infiltrometers and rain simulators. Additionally, it introduces the concepts of V and W indices, which measure the effectiveness of rainfall in generating surface runoff and the average infiltration capacity during rainfall, respectively.

Takeaways

• 😀 Infiltration is the flow of water into the soil, either laterally or vertically towards springs, rivers, lakes, or groundwater.
• 😀 Percolation refers to the downward flow of water into the groundwater through soil pores, influenced by gravity and capillary force.
• 😀 Soil moisture is the water content in the soil, which can either move upward as capillary water or downward as gravitational water.
• 😀 Infiltration capacity (FP) is the maximum amount of rainwater a soil can absorb, and it depends on factors like soil type, moisture, and surface conditions.
• 😀 If rain intensity is less than the infiltration capacity, all rainwater is absorbed into the soil, while excess water leads to surface runoff (SRO).
• 😀 Infiltration measurement can be done using tools like infiltrometers and rain simulators, which simulate rainfall to assess soil's infiltration ability.
• 😀 Infiltrometers use concentric cylinders inserted into the ground to measure the infiltration rate by maintaining a constant puddle height in the middle ring.
• 😀 Rain simulators create artificial rain at a controlled intensity, and the overflow is measured to calculate the soil's infiltration capacity.
• 😀 Infiltration capacity is calculated using the formula FP = FC + f0 * e^(-k * Delta t), where FC is constant infiltration capacity, and f0 is the initial infiltration capacity.
• 😀 The V index measures the average rain intensity, indicating the volume of rain that causes surface runoff (discharge), while the W index represents the average infiltration rate during rain.
• 😀 The effective rainfall is the portion of the rain that contributes to surface flow, and the flow coefficient (Alpha) is the ratio of effective rain to total rain.

Q & A

What is infiltration in hydrology?

Infiltration refers to the flow of water into the soil through the soil surface. It can flow laterally as interflow towards springs, rivers, or lakes, or vertically, known as percolation, towards groundwater.

What factors influence the movement of water through the soil?

The movement of water through soil is influenced by gravity, which causes water to move downward, and capillary force, which causes water to move in all directions.

What is the term used to describe the maximum ability of the soil to absorb rainwater?

The term used is 'infiltration capacity' (FP), which is the maximum rate at which a specific type of soil can absorb rainfall.

What happens when rain intensity is less than the infiltration capacity?

When the rain intensity is less than the infiltration capacity, all the rain will be absorbed into the soil, and there will be no surface runoff.

What is the meaning of 'f0' in the context of infiltration?

'f0' represents the infiltration capacity at the start of the rain, and it is equal to the rain intensity (i) when the rain begins.

How does the infiltration capacity change when the soil becomes wet?

As the soil becomes wet, the capillary forces decrease, causing the infiltration rate to slow down. Eventually, the infiltration capacity reaches a constant value influenced mainly by gravity and percolation.

What tools are used to measure infiltration capacity?

Infiltration capacity is measured using infiltrometers and rain simulators. An infiltrometer typically consists of two concentric cylinders, while a rain simulator creates artificial rain to test the soil's absorption ability.

What is the function of the outer ring in the infiltrometer?

The outer ring of the infiltrometer functions as a saturator for the surrounding soil, ensuring that seepage in the middle ring is vertical, representing more accurate infiltration conditions.

What is the formula used to calculate infiltration capacity (FP) during heavy rain?

The formula to calculate FP is FP = FC + (f0 + fcup) * e^(-k * Delta t), where FC is the constant infiltration capacity, f0 is the infiltration capacity at time T0, k is a constant specific to soil and surface conditions, and t is the time in minutes since the rain started.

What does the V index represent in hydrology?

The V index represents the average rain intensity at which the upper part of the rain volume is the same as the volume of surface flow. It helps in understanding the relationship between rain intensity and runoff volume.