Civil Engineering: Rainfall Simulator

Rainfall Simulators

• Used to measure infiltration rates by simulating rainfall on a small plot of land (2m x 4m) with nozzles producing raindrops from a height of 2m
• Various intensities and durations of rainfall can be simulated
• Surface runoff is measured and infiltration rates are calculated using water budget equations

Sprinkler Infiltration Method

• Similar to irrigation by sprinkler, where the rate of application is equal to or more than the infiltration rate of the soil

Basin Ponding Method

• Similar to the cylinder method, but uses a circular or rectangular basin instead
• Used in Vertisols where infiltration rates are low and basin or border irrigation is practiced
• Water is introduced into the basin to a depth of 12cm and the water level is recorded using a hook gauge

Factors Affecting Infiltration

• Surface roughness and sealing can affect infiltration rates
• Heavy rainfall can result in little infiltration before runoff
• Steady rainfall can result in more water infiltrating into the soil before runoff

Single Ring Infiltrometer

• Consists of a single cylinder with a diameter of 30cm and a depth of 25cm
• Infiltration is measured by pouring water into the cylinder and measuring the quantity of water added over time
• Lateral movement of water is not restricted, resulting in large variations in infiltration rates

Double Ring Infiltrometer

• Consists of two concentric cylinders to reduce lateral movement of water
• Water is filled in the outer cylinder to the same height as the inner cylinder to avoid lateral flow
• Provides more accurate results, but can disturb the soil and cause unnatural seepage

Hydrograph Methods

• Determine infiltration rates by analyzing rainfall and runoff data from a catchment area
• Infiltration rate is obtained by subtracting surface runoff from rainfall
• Total volumes of infiltration and other losses can be obtained from a discharge hydrograph