Figure 4-2. Actual and simulated hydrograph of Subbasin 5. The simulated peak discharge and volume were very close to the actual values with only around 2.7 and 3.4% difference‚ respectively. This shows that the simulations were accurate. Moreover‚ Figure 4-2 shows that the simulated hydrograph follows the same pattern as the actual hydrograph; including the same time to peak and peak discharge although the rising limb is not that steep as in the actual hydrograph. The lag time between peak rainfall
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The shape of the hydrograph varies according to a number of controlling factors in the drainage basin A number of factors (known as drainage basin controls) influence the way in which a river responds to precipitation and have an effect on the shape of the hydrograph. The size‚ shape and relief of the basin are important controls. Water takes longer to reach the trunk stream in a large‚ round basin than in does in a small‚ narrow one Where gradients are steep‚ water runs off faster‚ reaches
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Factors Influencing the Storm Hydrograph 1 | Geology of catchment area | | Geology | Lag Time | Rising Limb | Peak Discharge | Recession Limb | | Permeable rocks | Long | Gentler | Low | Gentler | | Impermeable rocks | Short | Extremely steep | High | Steeper | | Permeable rocks possess more concentrated lines of weaknesses and preexisting joints that can be exploited by water. Water flow along these open cracks and pathways within the rock is
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Physical Factors on the Storm Hydrograph The Storm Hydrograph refers to graphs that show how a drainage basin responds to a period of rainfall. Storm hydrographs are very important in predicting the flood risk and in making the necessary precautions to avoid damage to property and loss of life. Physical factors are the biotic factors which affect organisms and their surroundings‚ their surroundings in this case being the drainage basin and therefore the storm hydrograph is affected. These physical
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Qp tc tc +td • Experience has shown that the Rational Method can provide satisfactory estimates of peak discharge on small catchments of up to 80 hectares. For larger catchments‚ storage and timing effects become significant‚ and a hydrograph method is needed. • Assumptions used in the Rational Method are as follows: 1. The peak flow occurs when the entire catchment is contributing to the flow. 2. The rainfall intensity is the same over the entire catchment area. 3. The rainfall
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approaches: the Rational Method‚ the US Soil Conservation Service (SCS) method‚ and the unit hydrograph. Here we discuss the Rational Method and one approach presently used in New Zealand that employs both the SCS and unit hydrograph methods. 4.2.1 Unit hydrograph and SCS methods The unit hydrograph method reflects how a catchment converts a hyetograph (a graph of the distribution of rainfall over time) into a hydrograph (a graph showing changes in river flow over time)‚ while the SCS method empirically
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channel flow. Hence‚ this essay seeks to compare urbanization and the various human and physical factors stated above come into place to determine the velocity and volume of the flows to and within the river channel‚ and the degree of impact on hydrographs. Through this‚ it can be seen that urbanization as a human factor are more influential than physical factors in a casualty scale in affecting the flows within a river as they are able to override the impact of physical factors themselves. The
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application of the method is in estimating quantities of runoff in flood hydrographs or in relation to flood peak rates. These quantities consist of one or more types of runoff. An understanding of the types is necessary to apply the method properly in different climatic regions. The classification of types used in this handbook is based on the time from the beginning of a storm to the time of the appearance of a type in the hydrograph. Four types are distinguished: Channel runoff occurs when rain falls
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GCSE Geography| Topic 2| Water On The Land What are the Key Ideas for this Topic? The Shape of river valleys changes as the river flows downstream River Features & Landforms Storm Hydrographs Flooding in MEDC’s and LEDC’s Hard and Soft Strategies for River Management and Reservoirs The Shape of river valleys and River Processes A rivers long profile changes over its course. Every river has: An Upper Course Middle Course Lower Course Long Profile- shows how the gradient
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a. Loss Method: NRCS Curve Number Method The U.S. Natural Resource Conservation Service (NRCS) (formerly the Soil Conservation Service (SCS)) Curve Number method used in this study estimates the effective rainfall as a function of the cumulative rainfall‚ the land use‚ the soil type and the antecedent moisture condition of the soil. The model is described in detail in the National Engineering Handbook (NEH) (NRCS 2004). It was created based on the analysis of a large number of small and gauged agricultural
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