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    Infiltration Indices and Flood Wave

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    ashan
    This document discusses infiltration and infiltration indices in hydrology. It defines infiltration as water entering the soil at the ground surface. The infiltration approach to runoff estimation assumes surface runoff equals rainfall not disposed of through interception, depression storage, evaporation, or infiltration. Horton's equation models the declining infiltration rate over time. Infiltration indices (φ-index) represent the rainfall rate above which rainfall equals runoff volume, accounting for all losses. The φ-index divides a storm hydrograph into net rainfall and losses. Examples demonstrate calculating runoff from rainfall data using the φ-index.

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    Infiltration Indices and Flood Wave

    Uploaded by

    ashan
    20 views7 pages
    This document discusses infiltration and infiltration indices in hydrology. It defines infiltration as water entering the soil at the ground surface. The infiltration approach to runoff estimation assumes surface runoff equals rainfall not disposed of through interception, depression storage, evaporation, or infiltration. Horton's equation models the declining infiltration rate over time. Infiltration indices (φ-index) represent the rainfall rate above which rainfall equals runoff volume, accounting for all losses. The φ-index divides a storm hydrograph into net rainfall and losses. Examples demonstrate calculating runoff from rainfall data using the φ-index.

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    This document discusses infiltration and infiltration indices in hydrology. It defines infiltration as water entering the soil at the ground surface. The infiltration approach to runoff estimation assumes surface runoff equals rainfall not disposed of through interception, depression storage, evaporation, or infiltration. Horton's equation models the declining infiltration rate over time. Infiltration indices (φ-index) represent the rainfall rate above which rainfall equals runoff volume, accounting for all losses. The φ-index divides a storm hydrograph into net rainfall and losses. Examples demonstrate calculating runoff from rainfall data using the φ-index.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    20 views7 pages

    Infiltration Indices and Flood Wave

    Uploaded by

    ashan
    This document discusses infiltration and infiltration indices in hydrology. It defines infiltration as water entering the soil at the ground surface. The infiltration approach to runoff estimation assumes surface runoff equals rainfall not disposed of through interception, depression storage, evaporation, or infiltration. Horton's equation models the declining infiltration rate over time. Infiltration indices (φ-index) represent the rainfall rate above which rainfall equals runoff volume, accounting for all losses. The φ-index divides a storm hydrograph into net rainfall and losses. Examples demonstrate calculating runoff from rainfall data using the φ-index.

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    of 7

    HYDROLOGY

    Infiltration indices

    Asst. Lec. Ali Abdul-Hussein Abed


    Fourth year
    1

    Infiltration
    Water entering the soil at the ground surface is called infiltration
    Infiltration approach to Runoff estimation
    The infiltration approach assumes the surface runoff from a given storm is
    equal to the portion of the rainfall which is not disposed of through:
    1. Interception and depression storage,
    2. Evaporation during the storm, and
    3. Infiltration.
    Horton’s equation:

    𝑓 = 𝑓𝑐 + (𝑓𝑜 – 𝑓𝑐 )𝑒 –𝑘𝑡
    𝑓𝑜 − 𝑓𝑐
    𝑘=
    𝐹𝑐
    Where,
    f0 = initial rate of infiltration capacity
    fc = final constant rate of infiltration at saturation
    k = a constant depending primarily upon soil and vegetation
    Fc = shaded area in Fig below.
    t = time from beginning of the storm

    Ali Abdul-Hussein Abed


    2

    If items of Interception and evaporation are constant or insignificant, so there is one


    concerned only with rainfall, infiltration and runoff.

    Example: - For a given basin, the following are the infiltration capacity rates at various
    time intervals after the beginning of the storm. Make a plot of the f-curve and establish
    an equation of the form developed by Horton. Also determine the total rain and the
    excess rain (runoff).

    Ali Abdul-Hussein Abed


    3

    Ali Abdul-Hussein Abed


    4

    Infiltration Indexes (∅ − 𝒊𝒏𝒅𝒆𝒙):


    That rate of rainfall above which the rainfall volume (depth) equals the runoff volume
    (depth). ∅ − 𝑖𝑛𝑑𝑒𝑥 is relatively simple and all losses due to infiltration, interception
    and depression storage (i.e., storage in pits and ponds) are accounted.
    Estimates of runoff volume from large areas are sometimes made by the use of
    infiltration indices, which assume a constant average infiltration rate during a storm,
    although in actual practice the infiltration will be varying with time.

    Ali Abdul-Hussein Abed


    5

    Provided i > ∅ throughout the storm. The bar graph showing the time distribution of
    rainfall, storm loss and rainfall excess (net rain or storm runoff) is called a hyetograph,
    Fig. below. Thus, the ∅-index divides the rainfall into net rain and storm loss.

    Example: given 𝑖 = 1.8 𝑐𝑚/ℎ𝑟 rainfall intensity and ∅ − 𝑖𝑛𝑑𝑒𝑥 = 0.6 𝑐𝑚/ℎ𝑟. Find
    direct runoff of the basin.
    Solution:

    Example: Given DR = 1.3 cm required find ∅ − 𝑖𝑛𝑑𝑒𝑥 from the following data:
    Time (hr.) 1 2 3 4 5 6
    Precipitation 1.2 2.1 0.4 0.8 1.6 1.4
    (cm/hr.)
    Solution:

    Ali Abdul-Hussein Abed


    6

    Example: Find ∅ − 𝑖𝑛𝑑𝑒𝑥 for the following data which representing rainfall intensity
    for a 1-hr Unit Hydrograph:
    Time (hr.) 0-1 1-2 2-4 4-8
    Rainfall intensity (mm/hr.) 5 9 8 3

    Ali Abdul-Hussein Abed

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