VVR111 – Hydrology and Aquatic Ecology. Rainwater Collection Calculation Formulas and Equations. Therefore, it may be noted from the illustrative example that the peak run-off is very much dependent on the nature of the catchment, other factors remaining the same and varies from 400 cum/sec to 3204 cum/sec when the degree of porosity and absorption of the catchment area is very high or very low. Delineate the boundary of a catchment/contributing area using a Digital Elevation Model and a given point (a specific point for which we want to find the contributing/catchment area). Does rainfall correlate with known modes of climate variability (i.e. the distance from the rain-gauge to the centre of the representative area. Report a Violation, Top 6 Methods for Estimation of Flood Discharge, Design Flood: Definition and Computation of Design Flood Hydrograph. C = Constant. Here you can easily find how much rainwater you can collect from you roof, how much you need to remove from a courtyard, or how much runoff you can expect from an area of land. \mathrm{ADR\ (mm)\ =\ }\frac{\sum{A_i\ast P_i}}{\sum A_i} Click on “Monthly observations” and go to Precipitation CRU TS 0.5. First Approach The general form of the empirical formulae Q = CAn where Q = flood discharge, A = catchment area, C = flood coefficient and n = flood index Both C and n depend upon various factors, like Size, Shape, Location and Topography of catchment Intensity, Duration and Distribution pattern of the storm (continued) 7. Copy and paste the annual totals from the PIVOT table (include the year and amount columns) into another sheet. You will then be emailed a zip file of the station’s data. If land use and soil cover are homogeneous over the drainage area, a … Select Year and Rainfall amount as the FIELDS. We want to ensure that there are only whole years to calculate the sums or else they will be in error. SOI is calculated as follows. In order for this command to produce a catchment area, the surface triangle edges must form a channel that slopes toward the discharge point. Download the answer sheet for this exercise by clicking the download button in the tool bar . area, channel length, channel slope, percentage of impervious area, and percentage of the basin served by detention. The values of H and L can be found from the contour map of the catchment area. In order for this command to produce a catchment area, the surface triangle edges must form a channel that slopes toward the discharge point. Remember the relationship between rainfall and discharge as outlined in the lecture. The catchment area is F = 3200 km2, the average annual discharge in the year of 2004 is Q = 85 m3/s, the average annual precipitation P = 1245 mm, try to calculate the following value of this catchment in 2004. A river has the bed levels at the highest flood at certain intervals as shown in Fig. The annual rainfall varies from place to place and therefore, the recorded rainfall for a considerable period, say fifty years, is very useful in getting the maximum rainfall recorded during this period. We then look at how rainfall may be changing over time and how it varies over space across Western Australia. 4.1.2 Catchment protection Catchment protection is the second step in providing safe drinking water and where, for whatever reasons, source choice is limited it presents a key opportunity to minimise pathogen contamination. It is also called catchment or drainage area. Select the required data across multiple columns (year C to rainfall amount F). age area to depend on the group. Do they correlate in specific seasons? A … Select the all years of data and INSERT a SCATTER plot. Drainage area was the only sig - nificant variable in the revised regression equations. (8 marks). (2 marks), Use the Data Analysis add-in to calculate descriptive statistics (mean annual rainfall, max annual rainfall, min annual rainfall, Standard deviation of annual rainfall, Skewness) for the whole data (you can install by going to Tools->Add-ins->Analysis ToolPack). Rational Method: If R is the total rainfall in cm for a duration of T hours then the mean intensity of … Privacy Policy 8. The best way to calculate discharge of a river is to measure it. In the present case for catchment area composed of sandy soil with thick vegetation, A = 800 sq.km = 80,000 hectares ; P from table 3.3 = 0.10 ; f from table 3.4 = 0.60 ; Ic = 2.98 cm/hour. Next the Attenuation outflow must be specified. Prohibited Content 3. The expo-nents for the drainage-area ratio were 0.85 for the winter season, 0.91 for the spring season, and 1.02 for the summer season. In order to calculate the flow discharge produced by a large storm (convective type) in the catchment in, it is necessary to calculate the average depth of rainfall (ADR) over the catchment. Click on “Correlate with a time series” and choose either SOI or DMI. A = Area … So, watershed area is the land area, from where all the surface runoff converges to a single point to give common discharge. The flood discharge can be evaluated by using various empirical formulae involving area of the catchment and some coefficient depending upon the location of the catchment. What variability can you see? The analyses resulted in a relation that can be used for estimating storm peak discharge based on drainage area, basin-average rainfall, and impervious area… Then click correlate at the bottom and wait (the calculations are being done online and the graph returned for viewing). A … 3.1 and Fig. the characteristics of the local storm patterns (convective versus low intensity events). Para 4.2.2 The design discharge (Q) normally shall be computed flood with a probable recurrence interval of 50 years. This value may be compared with the theoretical worked out value and a final value may be selected. The possibility of intensive rainfall falling simultaneously over the entire area of a big catch­ment is less and therefore, a lesser percentage of run-off may be taken. The average depth of rainfall (ADR) over the entire catchment can be calculated using: Where \(A_{i}\) is the polygon area (km2), \(P_{i}\) is the rainfall (mm) corresponding to the \(i\) polygon, and \(\sum{A_{i}}\) is the catchment area (km2). The followings are the methods used to calculate discharge of a catchment area using rainfall data: Runoff Computation Methods.