At key river gages, such as along navigable rivers, daily forecast hydrographs are. What is the relationship isbetween precipitation andrunoff. Factors affecting hydrograph shape shrewsbury international. Key terms on the hydrograph, illustrated below, are.
Physical factors affecting flood hydrograph geography. O to be able to explain causes of flooding to be able to link causes and factors affecting flooding precipitation intense precipitation prolonged snowmelt explain what a flood hydrograph shows. Commonly known as storm hydrographs, flood hydrographs or simply. Understanding streamflow adeq sw short course june, 20 phoenix, az. Therefore, in unit hydrograph theory if you have a unit hydrograph derived for 100 mm of excess rainfall and the actual excess rainfall is. Learn vocabulary, terms, and more with flashcards, games, and other study tools. In addition, you win be shown how the engineering field manual efm and technical release55 ctr55 use a shortcut flood routing procedure to design small structures. Some rainfall is captured by soil and vegetation, and the remainder enters. A hydrograph shows how the river level changes over time at a specific location. Factors affecting flood frequency physical factors. Oct 18, 20 gcse geography project on factors which affect hydrographs.
When rain falls on a catchment, the amount of rainwater that reaches the waterways depends on the characteristics of the catchment, particularly its size, shape and land use. The maximum level of flood water or flow that occurs, on average, once every 100 years. Hydrographs and flood analysis worksheet answer key. The peak discharge is also lower as it takes water longer to reach the river channel. The size and shape of a rivers drainage basin dictates how much precipitation the river can receive and how quickly it will arrive the lag time. Drainage basins all have a variety of characteristics. Forecast hydrographs are displayed when flooding is expected, otherwise the hydrograph for the past few days is provided, if the data are available.
Simulation of flood hydrographs for georgia streams. Hydrographs discharge understanding streamflow flood factors. Repeat step 6 to add hydrograph at point b cfs to the same plot. A circular shaped drainage basin leads to rapid drainage whereas a long drainage basin will take time for the water to reach the river. A hydrograph shows two graphs a bar chart showing rainfall, usually from a storm and a line graph showing discharge from before, during and after the rain storm shown in the bar graph. Some of the factors which must be considered on an individual sitebysite basis include the following.
A flood hydrograph and the factors that affect its form. Having discussed the concept of a hydrograph, it is important also to outline some of the factors that affect its shape. Surface runoff rainfall a hydrograph of a stream is the graphical representation of the instantaneous dis. Glue the spider diagram of factors affecting hydrographs into your folder, then use it to complete the questions below. A breach hydrograph can be natural recorded or synthetic a simulation. Lohani, scientist g, national institute of hydrology, roorkee247667.
Consideration is also given to the effect of such factois as climate, topography, and vegetation that determine the characteristics of hydrographs from melting snow. A striking paradox of geohydrological research is the contrast between the relative abundance of streamflow data, and the narrow range of conditions to which it applies. A hydrograph shows how the river level changes over time. The shape of a hydrograph is altered by a few different things. Flood analysis activityhydrographs and flood analysis worksheet answer key 2 7. Development of flood hydrographs for extreme rainfall events that can be used to design hydraulic structures such as bridges, culverts etc. Jul 01, 2006 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. Gcse geography project on factors which affect hydrographs. It can also refer to a graph showing the volume of water reaching a particular outfall, or location in a sewerage network graphs are commonly used in the design of. A method for simulating these flood hydrographs at ungaged sites in georgia is presented in this report.
Use the geographical information from the attached files and from the further sources indicated below to. Hydrograph is a graphical or tabular presentation of instantaneous runoffdischarge rate against time. Hydrograph due to isolated storm is typically single peaked with skewed distribution of discharge. Feb 07, 2007 there are multiple factors affecting the discharge and discharge rate of a river, particularly after a high amount of rainfall. The influence of landform and precipitation parameters on. Explain the different flood levels and lag time shown by the flood hydrographs of the three rivers. Aug 02, 2014 factors affecting flood frequency physical factors. They show the river discharge that occurs as a result of precipitation from an earlier storm. It is often recommended to plot the unit hydrographs that are to be averaged. Relief or gradient of the arethe steeper the slopes, the lower the rate of infiltration and faster the rate of runoff when the soil is saturated saturated overland flow or when rainfall intensity rate per unit of time is high infiltration excess over land flow. Sometimes, it is also known as storm hydrograph, flood hydrograph or simply hydrograph. Flood hydrographs and flood volumes commonly are needed for the design of highway drainage structures and embankments or where storage of floodwater or flood prevention is part of the design, additionally, hydrographs may be necessary to estimate the length of time of inun dation of specific features, for example, roads and bridges. Flood analysis activityhydrographs and flood analysis worksheet 2 7.
The odonnell method was used to compute unit hydrographs and lagtimes for 355 floods at 80 gaging stations. Synthetic generation of arbitrarily long series of flood hydrographs for flood risk assessment. A storm hydrograph is a way of displaying how the discharge of a river can change over time in response to a rainfall event. Factors affecting shape of hydrograph climatic factors form of precipitation rainfall and snow fall rainfall tends to produce runoff rapidly generating hydrograph with high peak and narrow base rainfall intensity affect volume of runoff, occurrence of peak flow, duration of surface flow. Storm hydrographs show river discharge around the time of a storm event. Factors affecting river regimes geography from ks3 to ib. Hydrology training series module 111 reservoir flood. Large drainage basins catch more precipitation so have a higher peak discharge compared to smaller basins. There is a range of human factors that affect the shape of a storm hydrograph. Storm hydrographs only cover a short period of time around a particular storm event hours and days rather than longer periods of time.
An introduction to flood risk and management p a g e 18 37 process, in that every fluvial system has its hydrograph type, a type of evolution that usually. Learning goalsknowledgeto know what a flood hydrograph isunderstandingto understand the factors affectinghydrograph shapeskillsuse key words to describe a flood hydrographhydrograph interpretation 3. Factors affecting the flood hydrograph mish mash of stuff i found on. Factors affecting the shape of the breach hydrograph include.
Based on resources from north west regional flooding resource. The rate of flow is typically expressed in cubic meters or cubic feet per second cms or cfs. Indented landscapes will collect water and reduce runoff rates, reducing the amount of water reaching the river channel. Then an average or representative unit hydrograph should. A hydrograph is a graph showing the rate of flow versus time past a specific point in a river, channel, or conduit carrying flow. Factors affecting shape of hydrograph climatic factors form of precipitation rainfall and snow fall rainfall tends to produce runoff. A numerical average of several unit hydrographs which are different shapes may result in an unrepresentative unit hydrograph. May 21, 20 lesson 6 factors affecting discharge hydrographs 1. Coincidentally, 1m 3 s1 is the same as 1 cumec so the discharge of a river is often measured in cumecs because its a bit easier to say. Give you opinion as to which of the above factors are important in influencing flooding in a river.
In modeling single floods, the effects of evapotranspiration, as well as the. Plotted on the graph is the amount of discharge over a period of time. By looking at a hydrograph, a lot of information and data can be gathered about the river, the precipitation, the surrounding area and vegetation etc. Lets take a look at these different flood hydrograph dynamics. The time distribution of runoff the shape of the hydrograph is influenced by climatic, topographic and geological factors. Flood hydrographs are graphs that show how a drainage basin responds to a period of rainfall. Evapotranspiration may be ignored because its magnitude during the time period in which the flood develops is. Factors affecting a storm hydrograph the drainage basin. Physical factors affecting storm hydrographs there are a range of physical factors that affect the shape of a storm hydrograph. Circular hydrographs are more likely to have flashy hydrographs. Hydrographs discharge understanding streamflow flood. There is time lag between the occurrence of rainfall and the time, when it passes the gauging station.
In modeling single floods, the effects of evapotranspiration, as well as the interaction between the aquifer and the streams, are ignored. Systematic changes in the flood hydrographs, brought about by controlled variation in the five factors previously mentioned, are described. A striking paradox of geohydrological research is the contrast between the relative abundance of streamflow data, and the narrow range of. Therefore, in unit hydrograph theory if you have a unit hydrograph derived for 100 mm of excess rainfall and the actual excess rainfall is 60 mm in the same unit time perio d, the.
Hydrographs interpretation of hydrographs bbc bitesize. Introduction rainfall after initial losses and infiltration losses are met, reaches the stream as runoff. Physical factors affecting storm hydrographs image demonstrating the difference between the hydrographs for elongated and circular drainage basins. Hydrographs show how the volume of water flowing at specific point in a river varies over time.
Since each of these hydrographs shows a response to a specific intensity and duration of rainfall, it would be useful to plot rainfall on this plot as well. In the hydrologic analysis for a drainage structure, the designer must recognize that there are many variables that affect a flood. This leads to the ground being saturated and runoff. Lesson 6 factors affecting discharge hydrographs 1. A flood hydrograph and the factors that affect its form a flood hydrograph is a graph of two axis, discharge and time. Roughly circular shapes are common as are more elongated and narrow shapes. Chapter 16 hydrographs 16iv 210vineh, march 2007 table 16b1 peak rate factor 600 16b1 table 16b2 peak rate factor 550 16b2 table 16b3 peak rate factor 500 16b3 table 16b4 peak rate factor 450 16b4 table 16b5 peak rate factor 400 16b5 table 16b6 peak rate factor 350 16b6. Probability density functions, stochastic models, gcms. Drainage basins come in a wide assortment of shapes. River flooding and hydrographs this resource helps students identify the main human and physical causes of flooding.
Drainage systems that have been created by humans lead to a short lag time and high peak discharge as water cannot evaporate or infiltrate into the soil. A large drainage basin means that the rivers catchment area is large so it will collect a lot of water, increasing discharge. Human factors affecting storm hydrographs there is a range of human factors that affect the shape of a storm hydrograph. Hydrographs are graphs that show river discharge over time. There are multiple factors affecting the discharge and discharge rate of a river, particularly after a high amount of rainfall. The range of characteristics can affect how likely a river within the basin will flood. Pdf synthetic generation of arbitrarily long series of. They are also used to show the hydrologic effects of existing or proposed watershed projects and land use changes. It seems simple, but what is the probability that a 100.
Rainfall is the most important factor in creating a flood, but there are many other contributing factors. Flood hydrographs are needed for the design of many highway drainage structures and embankments. A technique incorporating the dimensionless hydrograph is defined for simulating flood hydrographs for small rural and urban basins in missouri. Chapter 2 physical factors affecting hydrology hydrology manual 7 january 2006 orientation before returning to its former course. The discharge of a river or stream is the volume of water that flows past a point in the rivers course per second. River discharge storm hydrograph a level geography. Runoff will increase after soil field capacity is met which means water will reach the channel quicker. A flood hydrograph and the factors that affect its form 123. Flood hydrographs associated with future floodpeak discharges resulting from rainfallinduced runoff can be simulated, and estimates of basin lagtime and floodrunoff volume can be made.
The impacts of these factors on the shape of flood hydrographs is also shown through the use of a card sort activity. There are various factors to consider when explaining a hydrograph. The regime of a river is the way in which the discharge of the river changes over time or in the course of the year. The volume is measured in cubic metres m 3 and its per second so the units of discharge are cubic metres a second or m 3 s1. They are used to plan for flood situations and times of drought. Factors affecting the flood hydrograph mish mash of stuff i found on tesbbc website.
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