Dear Experts,
As we know that construction of unit hydrograph for a guged locations helps in discharge estimation, especially peak discharge.
I am interested to construct the unit hydrograph of a particular gauging site for which I have multiple rainfall runoff events. In order to construct unit hydrograph what are the criteria for selection of events and how to construct UH from these events. What is it's acceptability, mean how can we validate the constructed UH?
Dear Vikram,
Dr. Jochen has provided good information on the topic.
The following publications may also be useful
Dear Vikram:
Provided you believe in linear systems, the answer is a trial and error one. Start by selecting the pluviographs for the best gauged hydrographs you have. Within those, select the ones that the rainfall is "fairly" constant and closer to the unit time step. Then you apply the convolution and from there you get an estimate of the unit hydrograph. Each basin has its own response. So you try several times till you match results. If, you also have a good working level of mathematics and algebra, you construct a linear system of equations and go from there. My first book dealing with it was Hydrologie des Surface, a French book, over 50+ years ago. Good luck.
Carlos Mosconi, PhD, CE
Dear Experts
Thanks for your suggestions!!
Dr. Jochen, I would like to know why we have to select the specific UH for similar rainfall events, I think for a watershed is supposed to only one UH rather than different and then we have to obtain the UH for any duration rainfall. Can you please explain it.
Dear Vikram: The theory of the UH assumes that the time base of the UH is unique for each basin, but it is not necessary true for observed events. For different events (Duration, volume, temporal distribution, etc) it could correspond different UHs. If you have several measured events, it could be a nice research to analyse the dependence of UH characteristics compared with the characteristics of observed hydrographs. Regards
Dear friend,
First of all
The hydrograph is the graphical representation of the instantaneous flow of a watercourse as a function of time at the outlet of a watershed: It constitutes the basic concept
in hydrology.
The unit hydrograph (HU) is the flow hydrograph produced by direct runoff of an inch or millimeter, evenly distributed over the basin surface at a uniform rate for a short period of time.
Three fundamental parameters completely define the hydrograph:
ü rise time;
ü basic time;
ü peak flow
Nowadays, there are several distributed or global hydrological models with which one can quickly and accurately simulate any hydrograph.
HEC-HMS, GR4J,……………..
All my considerations
Dr. V.B.TRAORE, UCAD /SENEGAL
Dr. Vieux,
You have mentioned some basic and good points on hydrograph. Regards
Dear Vieux
Thanks for your discussion but still my queries is not answered? Can you let me know, what else we have to do if we obtain different UH for different events?
Is there any way to average out to characterize it for specific watershed. Please correct me if I am wrong somewhere in understanding of UH concept.
Dear Vikram,
I think that the most necessary was already said. I have only two comments. You are trying to find the shape of UH from measured data. First, I must emphasise, that you have to analyse the direct runoff (effective precipitation) and the separated hydrograph. The issue of separated hydrograph was already mentioned, the issue of effective precipitation was only touched. This means that you have to calculate the "losses". Depending on the complexity and local conditions, you can use for example SCS-CN method or some infiltration models. Before doing the analysis of rainfall-runoff, the volumes of effective precipitation and separated hydrograph should be equal. Second, you are doing the inverse calculation of the convolution. This can be solved even in the MS Excel. If you write the convolution in the array of cells summing them in one column or row then you can compare the shape of the hydrograph to the measured (and separated) one in a graph and numerically by calculating residuals. The convolution array should be linked to the vector (ordinates written in separate cells) of UH ordinates which can be then changed. You can then use the Solver to minimise the sum of residues by setting the UH ordinates as model variables (the cell with the sum of residues will be the objective function).
Hope, it will help.
Thanks Dear David...
Have to deeply analysed further to make some conclusive comment. Will follow the advice.
Article Influence of initial reservoir level and gate failure in dam...
Dear Vikram: a methodology similar to the proposed by David was applied in the article mentioned above.
Regards, Alvaro
This attachments will help you in the development of unit hydrograph usig the catchment gauged reach data.
are also possible. See the examples to construct UHG using multi-period rainfall events.
Cheers,
Gebiaw
The link below is excel sheet for derivation of UH example
Data Unit Hydrograph from Stream Flow Data: Spreadsheet
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