Geography
Storm Hydrographs
Storm hydrographs are graphs that show the change in a river's discharge over time in response to a storm event. They typically display a rapid increase in discharge as rainfall accumulates, followed by a gradual decrease as the storm passes. These hydrographs are important for understanding the impact of storms on river systems and for predicting potential flooding.
Written by Perlego with AI-assistance
11 Key excerpts on "Storm Hydrographs"
eBook - PDF- Thomas N. Debo, Andrew Reese(Authors)
- 2002(Publication Date)
- CRC Press(Publisher)
207 0-8493-XXXX-X/01/$0.00+$1.50 © 2001 by CRC Press LLC 7 Urban Hydrology 7.1 Introduction Hydrology is generally defined as a science dealing with the interrelationship between water on and under the Earth and in the atmosphere. For the purpose of this chapter, hydrology will deal with estimating flood magnitudes, volumes, and time distributions as the result of precipitation. In the design of stormwater management facilities, floods are usually considered in terms of peak runoff or discharge in cubic feet per second (cfs) and hydrographs as discharge per time. For structures that are designed to control volume of runoff, like detention storage facilities, or where flood routing through culverts is used, then the entire discharge hydrograph will be of interest. There are a large number of hydrologic procedures covering topics such as snow melt, precipitation, water supply, infiltration, drought, evapotranspiration, etc. In basic urban hydrology, procedures commonly used are reduced to: • Precipitation and losses • Peak flow determination • Flow hydrograph or volume determination • Hydrograph routing and combining • Storage routing Chapter 10 and Chapter 11 cover hydrograph routing and storage routine, respectively. This chapter covers the other three major topics. The analysis of the peak rate of runoff, volume of runoff, and time distribution of flow is fundamental to the design of drainage facilities. Errors in the estimates will result in a structure that is undersized and causes stormwater management problems, or oversized and costs more than necessary. On the other hand, it must be realized that any hydrologic analysis is only an approximation. The relationship between the amount of precipitation on a drainage basin and the amount of runoff from the basin is complex, and too little data are available on the factors influencing the rural and urban rainfall–runoff relation-ship to expect exact solutions.
- Mostafa M. Soliman(Author)
- 2010(Publication Date)
- CRC Press(Publisher)
133 7 Stream-Flow Hydrographs 7.1 INTRODUCTION Engineering hydrology is concerned primarily with three characteristics of stream flow: monthly and annual volumes available for storage and use, low flow rates that restrict the stream-based uses of water, and floods. Detailed analysis of flood hydro-graphs is usually important in flood-damage mitigation, flood forecasting, and estab-lishing design flows for many structures that convey floodwaters. 7.2 CHARACTERISTICS OF THE HYDROGRAPH The water that constitutes stream flow can reach the stream channel by any of sev-eral paths from the point where it first reaches the earth as precipitation. Some water flows over the soil surface as surface runoff and reaches a stream soon after its occurrence as rainfall. Other water filters through the soil surface and flows beneath the surface of the stream. This water moves more slowly than surface runoff and contributes to the sustained flow of the stream during periods of dry weather. In hydrological studies involving rate of flow in streams, these components of total flow must be distinguished. The first step in such studies is to divide the observed hydro-graphs of stream flow into components before analyzing the relationship between rainfall and runoff, determining the characteristic shape of hydrographs for a basin, or studying drought conditions. The route followed by a water particle from the time it reaches the ground until it enters a stream channel is devious. Three main routes of travel can be conveniently visualized: overland flow, interflow, and groundwater flow, as discussed in Chapter 5. Overland flow, or surface runoff, is the water that travels over the ground surface to a channel. The word channel here refers to any depression that may carry a small rivulet of water in turbulent flow during a rain and for a short while after.
eBook - ePubRainfall
Modeling, Measurement and Applications
- Renato Morbidelli(Author)
- 2022(Publication Date)
- Elsevier(Publisher)
This chapter first deals with the formation and separation of the flood hydrograph through the effective hyetograph associated to a specific rainfall-runoff event. On this basis the main structure of typical rainfall-runoff models for simulating single flood events is highlighted in general terms. Then, the specific structure of an adaptive rainfall-runoff model for real-time flood forecasting is also examined.Finally, through a synthetic statistical analysis of extreme rainfalls, a classical procedure for determining the design hydrograph of hydraulic structures is presented.13.2 Formation and separation of the flood hydrograph
The watershed, associated to a given river section, is constituted by drainage areas that contribute to the hydrograph formation at the outlet.A significant rainfall event, usually represented as a function of time by a histogram (hyetograph), produces a hydrological response at the watershed outlet. This response, denoted as hydrograph, is the continuous evolution in time of the stream discharge,QE(t ) (water volume per time unit, [L3 T–1 ]) (Dingman, 2015 ). It is noteworthy that, given a rainfall event occurring on a watershed, the volume of water associated to the hydrograph is only a fraction of the total input. A remaining water amount through the infiltration process increases the soil water content and could produce groundwater recharge that supplies at long times the river flow as baseflow (Fig. 13.1 ). A typical hydrograph shape is shown in Fig. 13.2 .Fig. 13.1 A schematic representation of the main mechanisms producing through the rainfall-runoff process the flood hydrograph at the basin outlet.Fig. 13.2 Example of a graphical procedure of hydrograph separation into baseflow and direct flow, given a rainfall-runoff event: r (t ) is the areal-average rainfall rate over the watershed andQE(t ) is the discharge observed at the basin outlet. For other symbols see text.At some time after the beginning of the rainfall the discharge begins to increase rapidly from the pre-event rate to a well-defined peak discharge,QE(tp), withtptime to peak. This part of the hydrograph is called the rising limb. This stage is determined by the effective rainfall starting from the time to ponding (Govindaraju and Goyal, 2022
eBook - PDF- Zekai Sen(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
Consequently, only a shallow depth of soil moisture penetration is achieved before pounding and the onset of surface runoff. Commonly, flood flows move down the channel network as a flood wave , flowing over a bed that is either initially dry or has a small initial flow. Hydrographs are typically characterized by extremely rapid rise times of as little as 15 to 20 min. However, transmission losses from flood hydrograph through bed infiltration are important factors in reducing the flood, and obscure the interpretation of observed hydrographs (Jordan, 1977; Parissopoulos and Weather, 1990; Ş orman and Abdulrazzak, 1993; Wheater, 2002). It is not uncommon for a flood to be observed at a gauging station, when further upstream a flood has been generated and lost to bed infiltration. Several synthetic hydrograph derivation methods are available (Snyder, 1938; Clark, 1943; Soil Conservation Service, 1971; 1986), but each has drawbacks in arid region applications because of the implicit assumptions in the derivations and loca-tion-specific conditions. Most of the methods in hydrology have two stages: logical and empirical. Any model is a simplified representation of a real hydrological system with a set of logical and empirical equations. The requirement from a model is the reproduction of the catchment scale relationship between storm rainfall and direct runoff. 4.7.2 L OGICAL P HASE Logically, there are relationships between the surface flow and catchment charac-teristics as mentioned in basic textbooks on hydrology (Linsley, 1982; Maidment, 1993). In practical studies, the two most important quantities are time-to-peak dis-charge and peak discharge, which are related to storm rainfall and drainage basin (wadi) features.
eBook - ePub- CIGB ICOLD(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
Figure 1.7 ) depending on the quartile. Statistical characteristics of temporal distribution of storms need to be analyzed to choose a quantile for a specific region. However, development of Huff method was originated at east-central Illinois (Akan and Houghtalen, 2003).- Triangular hyetograph methodThis method assumes that the temporal variation of precipitation intensity has a triangular shape as depicted in Figure 1.8 . A triangle is a simple shape for a design hyetograph. Once the design precipitation depth P and total duration T
dare known, the base length and height of the triangle are determined. The base length is Tdand the height h, so the total depth of precipitation in the hyetograph is given by P = 0.5Tdh (Chow et al., 1988).h =2 PT d(1.6) Figure 1.9 Procedure for estimating design precipitation- Alternating block method
The alternating block method is a simple way of developing a design hyetograph from an intensity-duration-frequency curve. The design hyetograph produced by this method specifies the precipitation depth occurring in n successive time intervals of duration Δt over a total duration Td= nΔt. After selecting the design return period, the intensity is read from the IDF curve for each of the durations Δt, 2Δt, 3Δt, …, and the corresponding precipitation depth found as the product of intensity and duration. (Chow et al., 1988).
1.2 Flood Hydrograph
A hydrograph is a continuous plot of instantaneous discharge vs. time at a given point along a water stream. It results from a combination of physiographic and meteorological conditions in a watershed and represents the integrated effects of climate, hydrologic losses, surface runoff, and baseflow (Bedient and Huber, 2003).1.2.1 Estimation of losses
- • Runoff Curve Number methodThe US Natural Resources Conservation Service (NRCS, 2004) has developed a widely used curve number (CN) procedure for estimating runoff. The NRCS CN model estimates rainfall excess as a function of cumulative rainfall, soil cover, land use, and antecedent moisture, using the following equation:
P e=2(P −)I aP −I a+ S
(1.7) where Pe=accumulated rainfall excess at time t; P =accumulated rainfall depth at time t;Ia=the initial abstraction (initial loss);
- Nicolas R. Dalezios(Author)
- 2017(Publication Date)
- IWA Publishing(Publisher)
Flooding impacts on where people choose to live, their ability to travel between places uninterrupted and stay connected, their livelihood and security, and from time to time causes enormous damage to property and infrastructure. When societies are not prepared or protected, flooding can have devastating results with widespread destruction of property and a great number of fatalities and population displacement. Floodings have been, and will always be, a persistent problem facing humanity. It cannot be eliminated or even avoided, but with proper understanding, preparedness and appropriate infrastructure development it can be protected against, or its impacts can be mitigated. This is what makes flood prediction a fundamental element of catchment hydrology.This chapter provides a basic understanding of floods and of the flood risk system, with a focus on small to intermediate size basin (with area less than 1000–3000 km2 ) which may be subject to flash floods. In this chapter we will not consider sewer floods, coastal floods and glacial lake outburst floods.4.1.1 The flood hydrograph and its shapeA typical flood hydrograph is represented in Figure 4.1 . Total streamflow during a precipitation event includes the baseflow existing in the basin prior to the storm and the runoff due to the given storm precipitation. Total streamflow hydrographs are usually conceptualized as being composed of:(i) direct runoff, which is composed of contributions from surface runoff and quick interflow;(ii) baseflow, which is composed of contributions from delayed interflow and groundwater runoff.Figure 4.1 Schematic description of a flood hydrograph.Surface runoff includes all overland flow as well as all precipitation falling directly onto stream channels. Surface runoff in many situations is the main contributor to the peak discharge. Interflow is the portion of the streamflow contributed by infiltrated water that moves laterally in the subsurface until it reaches a channel. Interflow is a slower process than surface runoff. Components of interflow are quick interflow, which contributes to direct runoff, and delayed interflow, which contributes to baseflow (e.g., Bras, 1990).
- Theodore V Hromadka II, Prasada Rao, Theodore V Hromadka II, Prasada Rao(Authors)
- 2018(Publication Date)
- IntechOpen(Publisher)
Chapter 1 Design Rainfall in Engineering Applications with Focus on the Design Discharge Nejc Bezak, Mojca Šraj and Matjaž Mikoš Additional information is available at the end of the chapter http://dx.doi.org/10.5772/intechopen.70319 Abstract Design hyetograph or design storm definition is one of the most important parts of the design discharge determination in case of ungauged catchments. Design hyetograph duration and temporal rainfall distribution can have large impact on the peak discharge values and the shape of the runoff hydrograph. The influence of these two factors on the design runoff values is presented in the case study of the Glinščica River catchment that covers 16.85 km 2 and it is located in central part of Slovenia, Europe. A combination of Huff and intensity-duration-frequency (IDF) curves is used to construct the design hyeto-graph for the presented case study. The duration of the design storm is determined by the catchment time of concentration. The results are compared to the Natural Resources Conservation Service (NRCS) curves and the so-called frequency storm method. The hydrological modeling result that was carried out using t he h ydrologic m odeling system (HEC-HMS) software indicates that differences among different methods should not be neglected. For the 10-year return period, differences in the peak discharge values can be larger than 10%, while even larger differences can be expected for longer return periods. Some studies showed that these can be larger than 50%. Therefore, the guidelines on how to construct the design hyetograph are presented. Keywords: design rainfall, design discharge, modeling, rainfall, hydrologic engineering 1. Introduction Design peak discharge values or in some cases, even the complete design hydrographs are needed for the design, planning, and construction of different hydraulic structures such as dams, water retention reservoirs, and levees that can be used to improve the flood safety.
eBook - PDF- Andy D. Ward, Stanley W. Trimble, Suzette R. Burckhard, John G. Lyon(Authors)
- 2015(Publication Date)
- CRC Press(Publisher)
ANSWER The hydrograph contains a runoff depth of 1.96 in., has a peak flow of 592.9 ft 3 /s at a time of 75 min, and has a total runoff time of 200 minutes. The hydrograph is illustrated in Figure 5.22. 201 Runoff and Drainage In Example 5.13 , the storm duration was longer than the lag time (60 minutes vs. 45 minutes). This causes an error in the solution as the shape of the hydrograph is primarily a function of the storm duration rather than the watershed characteristics. This problem can be prevented if knowledge is available of the rainfall time distribu-tion. The design storm rainfall depth is generally associated with a synthetic rainfall time distribution (refer to Figure 5.5 ). Rainfall excess can be determined using an infiltration equation or a procedure such as the NRCS curve number method ( Equations 5.9 through 5.11 ). The rainfall event should be divided into blocks of time that have a duration D that is not longer than one-third the time to peak of the unit hydrograph. Incremental storm hydro-graphs are then developed for each block of rainfall excess ( Figure 5.23 ). The incremental runoff hydrograph ordinates are equal to the volume of runoff for each block of rainfall excess times the unit hydrograph ordinates. The incremental Storm Hydrographs each start at the beginning of the block of rainfall excess with which they are associated. When all the incremental Storm Hydrographs have been established, the storm runoff hydrograph is obtained by adding the ordinates of the incremental hydrographs at each point in time. This is a time-consuming activ-ity subject to mathematical errors and is best performed by a computer program.
eBook - ePubFloods and Drainage
British Policies for Hazard Reduction, Agricultural Improvement and Wetland Conservation
- Edmund Penning-Rowsell(Author)
- 2019(Publication Date)
- Taylor & Francis(Publisher)
Floods are binary in that they are most influenced by two sets of factors: climatic and physiographic. Various studies have been undertaken to identify the relationships between these factors and flood characteristics, many involving multiple regression techniques designed to isolate the contribution different parameters make to peak flows (Potter 1961, Benson 1962, Rodda 1969). The three-dimensional nature of floods derives from their three significant characteristics, namely magnitude, frequency and timing. Much flood hydrology is concerned with the interaction between these characteristics.Magnitude/frequency studies are of vital importance in hydrological analysis (Natural Environment Research Council 1975); they also are fundamental to many areas of flood hazard research and the economic evaluation of flood alleviation schemes. Timing studies include hydrograph analysis (Weyman 1975) and flood routing (Lawler 1964). As Newson (1975) has indicated, there are situations when engineers need to predict the whole hydrograph rather than just the flood peak. This can occur when river flow records are short and longer rainfall records are used in the simulation of large floods using a hydrograph model and rainfall analysis techniques, such as probable maximum precipitation, when knowledge of flood duration is needed. Knowledge of the whole hydrograph is also needed for real-time forecasting of floods using instantaneously recorded data on catchment rainfall, perhaps from weather radar and linked to flood warning systems (Newson 1975). Knowledge of flood volumes, rather than just the size of peaks, is also needed when designing reservoir storage for water supply or as a flood-alleviation strategy.EARLY WORK
An important analysis of flood hydrology research before 1965 is provided by Wolf (1966) who reviews both the early magnitude studies and the subsequent frequency investigations.Attempts were made in the early 20th century to establish predictive flood magnitude relationships using relatively simple formulae. The fastest developments occurred in relation to the design of urban storm sewers and many formulae from early analyses relate peak flows to catchment area. Probably the most widely used in Britain is from the Institution of Civil Engineers’ 1933 Committee Report. While briefly considering flood frequency, and the effects of catchment character and precipitation on the flood hydrograph, this report concluded that ‘the only acceptable method for presenting flood information consisted of plotting recorded instantaneous peak flows against the contributing surface catchment areas’ (Institution of Civil Engineers 1933). The Institution’s report used the common formula:
eBook - PDFAtmosphere, Ocean and Climate Dynamics
An Introductory Text
- David H. Miller, John Marshall, R. Alan Plumb, J. Van Mieghem(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
To the dimensions of duration, depth, and intensity employed in Chapter III we now add the wetted area of the earth's surface. Areal rainfall is less easily measured than is point rainfall. About 1945, wartime radar was being reconverted to meteorological employ-ment, particularly for watching moving rain-generating cells. It has 64 THE AREA OF HYDROLOGIC STORMS 65 since been much improved for this purpose (as well as for monitoring severe local storms), and a montage of photographs or a radar plan-position indicator scope taken every 6 min gives an idea of the size of the hydrologie storm. In spite of great efforts over three decades to develop quantitative measures of rainfall, radar data, however, remain pictures more than numbers. The hope that was raised in 1945, that one radar set located on a ridge near the center of a mountainous drainage basin would read out the integrated input of atmospheric water into any subbasin or into the whole basin itself, is slow in coming. Measurement of hydrologie storms still begins with readings of point rainfall by gages of one kind or another; the readings are integrated, with all their errors and uncertainties, by procedures to be described later. THE AREA OF HYDROLOGIC STORMS The concept of a storm as a hydrologie entity combines the factor of the area of the atmospheric system itself with its movement during its life span. Let us look first at the areal dimension of a small storm that moved relatively little during its short life. Table I presents information on the areas receiving rainfall over several periods of time during a heavy storm over Sydney. These data purposely are limited to figures announced to the general public by radio and newspaper, in order to illustrate how even such fragmentary data can be made more meaningful when it is put into a framework of duration, depth, and wetted area of the storm unit.
eBook - ePub- Michael R. Lindeburg(Author)
- 2019(Publication Date)
- PPI, a Kaplan Company(Publisher)
Chapter 7 . Hydrology and HydrogeologyContent in blue refers to the NCEES Handbook.- 1. Hydrologic Cycle
- 2. Storm Characteristics
- 3. Precipitation Data
- 4. Estimating Unknown Precipitation
- 5. Time of Concentration
- 6. Rainfall Intensity
- 7. Floods
- 8. Total Surface Runoff from Stream Hydrograph
- 9. Hydrograph Separation
- 10. Unit Hydrograph
- 11. NRCS Synthetic Unit Hydrograph
- 12. NRCS Synthetic Unit Triangular Hydrograph
- 13. Espey Synthetic Unit Hydrograph
- 14. Hydrograph Synthesis
- 15. Nomenclature
1. Hydrologic CycleThe hydrologic cycle is the full “life cycle” of water. The cycle begins with precipitation , which encompasses all of the hydrometeoric forms, including rain, snow, sleet, and hail from a storm. Precipitation can (a) fall on vegetation and structures and evaporate back into the atmosphere, (b) be absorbed into the ground and either make its way to the water table or be absorbed by plants after which it evapotranspires back into the atmosphere, or (c) travel as surface water to a depression, watershed, or creek from which it either evaporates back into the atmosphere, infiltrates into the ground water system, or flows off in streams and rivers to an ocean or lakes. The cycle is completed when lake and ocean water evaporates into the atmosphere.The water balance equation (water budget equation ) is the application of conservation to the hydrologic cycle.7.1The total amount of water that is intercepted (and subsequently evaporates) and absorbed into ground water before runoff begins is known as the initial abstraction . Even after runoff begins, the soil continues to absorb some infiltrated water. Initial abstraction and infiltration do not contribute to surface runoff.Equation 7.1can be restated asEq. 7.2.7.22. Storm CharacteristicsStorm rainfall characteristics include the duration, total volume, intensity, and areal distribution of a storm. Storms are also characterized by their recurrence intervals. (SeeSec. 7.6.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
