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Hydrologie Cycle and Rainfall-Runoff Processes
Published in Monzur A. Imteaz, Urban Water Resources, 2019
Rating curve is the stage-discharge relationship at a particular section of a stream/river. If the stream/river cross-section and slope remain same, then this relationship would also remain the same. Figures 2.21 and 2.22 show typical rating curves in normal scale and in logarithmic scale, respectively. It is to be noted that, in the rating curves, vertical axis is usually not the depth of water, rather it is the stage (i.e. level or reduced level), which is measured with respect to a certain datum level (Mean Sea Level is usually taken as such datum). In Australia, such datum and measurement standard is called Australian Height Datum (AHD). Every country should have such datum fixed for their referencing for the presentations of elevations. A rating curve can be represented by the following equation: Q−a*(H−b)n
Streamflow and floods
Published in Stephen A. Thompson, Hydrology for Water Management, 2017
Routine measurements of streamflow are obtained through the use rating curves. A rating curve is a relationship between river stage and river discharge. Rating curves are developed through the simultaneous measurement of stage and discharge. Once the rating curve is defined, discharge is determined directly from measurements of stage. This obviously makes estimating discharge much easier. For most rivers a simple curve of stage versus discharge is satisfactory (Linsley et al. 1982). The best location for establishing a rating curve is where the channel cross-section is stable and not subject to variation in shape during high flows or affected by backwater. On streams with alluvial channels floods can scour the bed and banks changing the rating curve. Near tributary junctions high flows on one channel my cause backwater effects on the other. Gaging stations should be located far enough upstream to be beyond the influence of backwater. Linsley et al. (1982) discuss methods for correcting for these conditions of ‘shifting control’. Figure 11.37 is an example of a rating curve for Swarr Run.
River action and control
Published in F.G. Bell, Geological Hazards, 1999
The total volume of water or discharge flowing past a given point in a given time is the product of the cross-sectional area of the stream and its velocity. If the stream bed and banks have been accurately surveyed at the place of measurement, only data on the stage of the stream are needed to enable the cross-sectional area of the water in the stream channel to be calculated. The volume of discharge is calculated once the mean velocity of the current is known. Discharge can be measured accurately by means of a weir or flume on streams where a physical obstruction in the channel is permissible. If a continuous record of discharge is required, then it must be correlated with river stage. When discharge is plotted against corresponding stages, the curve drawn through plotted points is referred to as a rating curve (Figure 6.8). In other words, a rating curve is a graph relating the stage of a river channel at a certain cross-section to the corresponding discharge at that section. Hence, it can be used to estimate the quantity of water passing a particular location at a given time. When this ratio is greater than 1.0, flood conditions are imminent. A rating curve can be used to predict the severity of flooding as measured by the height of the flood wave that overtops bankfull height. This information can then be added to the curve developed from calculation of the frequency of flooding as related to discharge. This establishes the recurrence interval for floods of different magnitude. Using these data it can then be determined which parts of the floodplain will be affected by a storm of a given intensity and duration.
Freshwater management in Aotearoa-New Zealand: is trading a viable option for water quantity allocation?
Published in Australasian Journal of Water Resources, 2022
Douglas Booker, Katherine Booker, Carla Muller, Channa Rajanayaka, Andre Konia
Water quantity accounting is a technically challenging task, with potentially high uncertainties when monitoring abstractions and river flows in real time. Stage-discharge relationships are often applied in the form of a rating curve to convert water level to river flow. However, rating curves contain uncertainties and may also become obsolete due to changes in riverbed height, which often occur in gravel-bed rivers during high flow events, or channel roughness, which often occurs in low slope channels with in-stream vegetation growth (McMillan, Krueger, and Freer 2012). The New Zealand national digital river network, which provides a spatial framework for predicting hydrological patterns, has been used for estimating historical river flows (McMillan, Booker, and Cattoën 2016), forecasted river flows (Cattoën et al. 2019), streamflow depletion from consented abstractions (Booker 2018), and streamflow depletion from recorded abstractions (Booker, Rajanayaka, and Yang 2019) but there is no standardised method for calculating streamflow depletion.
Spatial total load rating curve for a large river: a case study of the Tigris River at Baghdad
Published in International Journal of River Basin Management, 2020
Ammar A. Ali, Nadhir A. Al-Ansari, Qusay Al-Suhail, Sven Knutsson
Prediction of sediment load is of prime importance for river engineering and geomorphology (Recking 2009). It affects the driving fluvial processes (Cook et al. 2013). The sediment rating curve is the most common predictor used for estimating sediment transport with other prediction formulae. The sediment rating curve can be used for reconstructing long-term sediment transport records or compensating for missing data in existing sediment transport records (Walling 1977a, Asselman 2000). It is often used to provide a boundary condition in morphodynamic models. The usual procedure to establish a sediment rating curve is by collecting sediment samples over a wide range of discharges at a given cross-section of the river reach, and then using a regression technique to determine the best coefficients of the rating equation which is usually takes the form of a power function (Walling 1977b, Fenn et al. 1985).
A Brief review of flood forecasting techniques and their applications
Published in International Journal of River Basin Management, 2018
Sharad Kumar Jain, Pankaj Mani, Sanjay K. Jain, Pavithra Prakash, Vijay P. Singh, Desiree Tullos, Sanjay Kumar, S. P. Agarwal, A. P. Dimri
In addition to precipitation, a number of other errors and uncertainties can be substantial. For example, errors associated with the initial conditions (e.g. soil moisture) are particularly important when the models are applied to isolated storm events. In addition, any model updating or downscaling can create errors and uncertainties, as can infrastructure operations (Cloke and Pappenberger 2009). Errors can be introduced with the use of rating curves. Flood forecasts are generally given in the form of level (gauge data), while the hydrological models typically compute discharge. A rating curve is used to transform calculated flows to water levels. Generally, rating curves are developed with a limited number of discharge observations that may not cover extreme flood events, giving sufficient room for uncertainty. In addition, there can also be uncertainties in the gauge observations. Furthermore, operational uncertainty of a FFWS can be caused by erroneous or missing data, human processing errors, or unpredictable interventions (Krzysztofowicz 1999).