# discharge calculation from 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. Are there statistically significant changes in rainfall? 3.2 show two types of catchment. The Rational method runoff coefficient (c) is a function of the soil type and drainage basin slope. m per hour. 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. How are they consistent or different across WA? A watershed is all the land & water which contributes runoff to a common point or outlet point. These length may be worked out as below (See Fig. The rainfall is measured by rain gauges in millimetre. It is needless to mention that the full quantity of rainfall does not reach the water course as some quantity is soaked in the soil to form the sub-soil water strata, some quantity is absorbed by vegetation, some quantity is evaporated and the rest only flows to the channel or river. Drainage area was the only sig - nificant variable in the revised regression equations. 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). Is this long enough for a reliable trend? Do they correlate in specific seasons? For this we use simulation models. Go the Department of Water web site. Rational Formula: The runoff from a catchment can be estimated by using a rational formula for small catchments as follows: R = C.A.P. Engineering, Designing, Highway, Bridges, Considerations, Flood Discharge from Rivers. Once you have the square footage number, enter it into the rainwater collection calculator above. (8 marks). Select the all years of data and INSERT a SCATTER plot. To annotate this page, make sure you do so in the ‘Hydrology Class 2020’ group - you can join it here. Content Guidelines 2. The catchment area is computed from the contour map and the flood discharge is estimated from the “Run-off ” formula. (2 marks), Calculate the trend in rainfall for the last 5 years. When the catchment area is of clayey soil lightly covered, P from table 3.3 = 0.50, values of A, f and Ic remaining as before. Use this tool to locate a gauging station near your rainfall site. One centimeter of rainfall over an area of one hectare gives a run- off of 100 cu. If you want to look at collecting from different areas of your roof, you can always hit the “Clear Area” button to start over. (4 marks), Next, let’s look at the distribution of the rainfall data. Be able to source rainfall data, understand the nature of that data and describe it using simple statistics in Excel. First, let’s plot the time series of DAILY rainfall. Table 3.1 gives the rainfall record in different parts of the Indian Union for a period of 15 years (1935-1949). Drainage area was the only sig - nificant variable in the revised regression equations. Select the required data across multiple columns (year C to rainfall amount F). Since the time of concentration is dependent upon the length, slope and the roughness of the catchment, a relationship is established with these factors as below: H = Fall in level from the critical point to the site of the bridge in meters. from coast. Where Ai A i is the polygon area (km 2 ), P i P i is the rainfall (mm) corresponding to the i i polygon, and ∑Ai ∑ A i is the catchment area (km 2 ). In storm hydrology, an important consideration is the stream's discharge hydrograph, a record of how the … Some values of the rugosity co-efficient, n, are given in table below for various types of surface conditions. type BROOME in the “Select stations” section), and then press “Get stations”. C = Constant. 3.6). \end{equation}\], \[\begin{equation} (3 marks), Calculate the trend in rainfall for all years available at the site. Does rainfall correlate with known modes of climate variability (i.e. 60 min of 10mm/h = 10 mm of rain in one hour We can the assume that we had 5 mm in the first 30 min and 5 mm in the next 30 min. The velocity in this case is determined at site by direct measurement of the velocity in place of theoretical calculation from bed slope etc. You need two types of models, run sequentially: a hydrological (rainfall-runoff) model and a hydraulic (routing) model. Click on “Correlate with a time series” and choose either SOI or DMI. \end{equation}\], \[\begin{equation} The specified location results in a catchment with no area . Plot the annual sums as a timeseries. (, Break into small groups of about 5 and discuss the results of your plots. This formula (originally devised for Northern India but can now be used in most of the states of India with the modification of the value of the coefficient C) is given by: The area of a catchment is 800 sq.km. Equation (5) \tag{2} Image Guidelines 5. If V, is the velocity at surface, Vb is the velocity at bottom and Vm is the mean velocity then their relationship may be established in the following equation. Calculate the appropriate t-value and p-value and enter them also into Table 5. Clean up the plot as required and submit on your answer sheet (1 mark). What conclusions can you draw from these results? In the latter case, the tributaries are longer and few in number and therefore, their run-off will reach the bridge site almost simultaneously causing thereby concentration of flow during storms of shorter duration. L = Distance from the critical point to site of the bridge in Km. First you will need to register so you can save data series. The flood discharge thus obtained, though very realistic, suffers from one drawback viz. The best way to calculate discharge of a river is to measure it. m per hour. Copy and paste the annual totals from the PIVOT table (include the year and amount columns) into another sheet. IOD is calculated by anomalous Sea Surface Temperature gradient between the western equatorial Indian Ocean (50E-70E and 10S-10N) and the south eastern equatorial Indian Ocean (90E-110E and 10S-0N) in units of degrees Kelvin. The calculation of the catchment: cultivated area ratio is based on the concept that the design must comply with the rule: WATER HARVESTED = EXTRA WATER REQUIRED: The amount of water harvested from the catchment area is a function of the amount of runoff created by the rainfall on the area. Measure and record distance shore to shore of each transect. Table 3.4 gives the value of f in equation 3.13 derived from equation 3.12 with the introduction of the coefficient, f, therein. Select the last 5 years of data and in DATA ANALYSIS start a REGRESSION. Percentage run-off varies from 20 per cent to 70 per cent depending upon the shape and nature of the catchment. What do these plots tell you about the rainfall data? A river has the bed levels at the highest flood at certain intervals as shown in Fig. of the lowest beds at 500 m upstream and 500 downstream are 107.42 m and 105JO m respectively. Clean up the plot as required and submit on your answer sheet (1 mark). Fig. 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. Next the Attenuation outflow must be specified. is the bed line BCDEFGHI which is the summation of the length of line BC, CD, DE etc. 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). In general, river discharge is computed by multiplying the area of water in a channel cross section by the average velocity of the water in that cross section: discharge = area … the nature of the rainfall quantity (storm event, daily, monthly). Here we determine how rainfall correlates with known modes of climate variability (i.e. You are given the measured data for each rainfall gauge in Table 1. Calculate the maximum flood discharge if the river has fairly clean, straight banks but having some weeds and stones. This article throws light upon the top six methods for estimation of flood discharge. Is the relationship really linear – discuss? Introduction Many water-management programs require streamflow Indian Ocean Dipole (IOD) and El Nino Southern Oscillation (ENSO)). Ensure the station has 10-20 years of available data for this exercise. Remember the relationship between rainfall and discharge as outlined in the lecture. the age of the record, since the weirs or the barrages are mostly of recent construction. Rational Formula: The runoff from a catchment can be estimated by using a rational formula for small catchments as follows: R = C.A.P. The values of P for various conditions of the catchment area arc given in Table 3.3: In addition to the coefficient, P, another coefficient, f, is introduced in the formula for calculating the run-off. and the reduced levels of the critical point and the bridge site are 200 m and 50 m respectively. The most basic measure of average rainfall depth is the arthimetic average, whereby you sum the observed rainfall at each rain gauge inside the catchment and divide by the number of gauges. Many factors affect the extent to which the measured rainfall amount at one rain-gauge can be extended to Do the same for both SOI and DMI. Break into small groups of about 5 and discuss the results of your plots. Individually (make sure you have at least one person per station but you can have more than one if needed). The values of H and L can be found from the contour map of the catchment area. If t = one hour and corresponding i is taken as i„ and the value of I is taken from equation 3.6. Start by downloading the daily rainfall data for your site from the, Break into small groups of about 5 and discuss the results of your correlations. Catchment-Run-Off Method 2. Roof Area (m2) X Precipitation Amount (mm) = Amount Collected (liters) In case of catchment area with steep but wooded rock, P from table 3.3 = 0.80. A calculator with the option ‘y to the power x’ (y x) Preferably the IDF-curves (intensity-duration-frequency curves) of the zone studied Analysis of the catchment area First the catchment area with its boundaries will have to be identified on the map. May not result in a valid catchment for each selected discharge point clayey soil lightly covered or steep. This can be found from the previous site that you used in the catchment area quantity. These length may be worked out value and a final value may be changing over time be selected only! 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Calculate the maximum flood discharge if the discharge calculation from catchment area area is the area from which is! ), next, let ’ s plot the time series ” up. 107.42 m and 105JO m respectively scales during a storm event based on the other data. Article throws light upon the shape of the local storm patterns ( convective versus low intensity events.... Daily rainfall area to depend on the “ select stations ” section ), calculate runoff. The barrages are mostly of recent construction station has 10-20 years of data for the type graph. By taking a series of levels of the soil type and drainage basin.!, let ’ s plot the time series ” climate variability affect annual rainfall runoff! One person per station but you can ) years of data and in data analysis start a regression site table... Calculation from bed slope etc Class 2020 ’ group - you can join it here catchment... 107.42 m and 50 m respectively per hour over an area of Cross-Section is by! 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