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Preliminary design of the storage capacity of reservoirs based on a flow regionalization parameter

Preliminary design of the storage capacity of reservoirs based on a flow regionalization parameter Maria Manuela PORTELA, Technical University of Lisbon, IST,Portugal António de Carvalho QUINTELA, Technical University of Lisbon, IST, Portugal. 1- Introduction. Frame

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Preliminary design of the storage capacity of reservoirs based on a flow regionalization parameter

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  1. Preliminary design of the storage capacity of reservoirs based on a flow regionalization parameter Maria Manuela PORTELA, Technical University of Lisbon, IST,Portugal António de Carvalho QUINTELA, Technical University of Lisbon, IST, Portugal 1- Introduction. Frame 2 - The mean annual flow depth as a regionalization parameter of annual flows 3 - The mean annual flow depth as a regionalization parameter of monthly and daily flows 4 - Evaluation of flow series at ungauged watersheds 5 - Evaluation of the net storage capacity of reservoirs at ungauged watersheds 6 - Final remarks

  2. The evaluation of the available water resources is often fundamental for many hydrologic planning activities. For that purpose long stream flow series in natural conditions at strategic sections of the rivers are generally needed. • However, the stream gauging stations with long enough recording periods are scarce in Portugal and, most of the time, they do not coincide with the river sections where stream flow data are required. • However, the stream gauging stations with long enough recording periods are scarce in Portugal and, most of the time, they do not coincide with the river sections where stream flow data are required. • To overcome this situation, hydrologic deterministic models have been developed since more than 40 years to simulate stream flows from precipitation and from other hydrologic and climatic variables, as well as from parameters depending on physiographic characteristics of the watersheds. • To overcome this situation, hydrologic deterministic models have been developed since more than 40 years to simulate stream flows from precipitation and from other hydrologic and climatic variables, as well as from parameters depending on physiographic characteristics of the watersheds. • The values of these parameters are usually calibrated based on the comparison between simulated and observed flows, which means that, once more, stream flow data are required . . . Introduction. Frame of the study • The evaluation of the available water resources is often fundamental for many hydrologic planning activities. For that purpose long stream flow series in natural conditions at strategic sections of the rivers are generally needed.

  3. Introduction. Frame of the study (cont.) • In order to evaluate the surface water resources at river sections without stream flow records, the authors developed procedures based on regionalization criteria and that can be applied at the early stages of the water resources planning at ungauged watersheds to establish annual, monthly and daily flow series as well as to evaluate the net storage capacity of reservoirs.

  4. Introduction. Frame of the study (cont.) Those procedures utilize as a regionalization parameter the mean annual flow expressed as water depth over the horizontal projection of the watershed or MEAN ANNUAL FLOW DEPTH, H, which is obtained by dividing the mean annual flow volume, V, by the area, A, of the horizontal projection of the watershed. Watershed outlet H A Discharges, Q, along N years Mean annual flow volume

  5. Introduction. Frame of the study (cont.) Higher values of H Based on the analysis of the flow records at a large number of Portuguese stream gauging stations spread over the country and having long recording periods it was shown that themean annual flow depth, H, is closely related with the relative temporal variability– within the year and among the years – of the flow regime in Portuguese rivers. Mean annual flow depth Lower values of H

  6. … proved by means of the variation coefficient of the annual flow series, Cv (ratio between the standard deviation and the average, being a measure of relative variability), according to the following relationship: Being Cv a measure of the relative variability of the terms of a series the interannual variability of the flow increases(Cv ) as the mean annual flow depth decreases (H ), that is to say, the annual flows are more irregular when the watershed is located in a drier region. H as a regionalization parameter of annual flows Dependency between the relative temporal variability of the annual flows and the mean annual flow depth, H

  7. H as a regionalization parameter of annual flows (cont.) Annual level Based on the depen-dency between Cv and H, relationships provi-ding the annual flow with a given non- -exceedance probabi-lity only as a function of H values were esta-blished (Pearson type III law).

  8. … proved by means of the mean quadratic deviation of the monthly and daily flows, MQD, given by: Mean quadratic deviation (non-dimensional form) of the monthly flow in month i or of the daily flow in day i H mean annual flow depth (mm) Hi mean monthly/daily flow depth in year i (mm) H i,j flow depth in month/day j of year i (mm) m 12, for the monthly level, and 365, for the daily level H as a regionalization parameter of monthly and daily flows Dependency between the relative temporal variability of the monthly and daily flows and the mean annual flow depth, H

  9. H as a regionalization parameter of monthly and daily flows (cont.) • The series ofMQDin each stream gauging (with as many elements as the number of years with records) was characterized by its mean – MEAN MQD– and by its standard deviation –DEVI MQD. MONTHLY FLOWS DAILY FLOWS

  10. Being the mean quadratic deviation (either of the monthly flows or of the daily flows) as higher as more irregular are the flows it can be stated that, in average, the relative temporal variability of the monthly and daily flows increases as H decreases . H as a regionalization parameter of monthly and daily flows (cont.) The figures show that … THE MEAN MQD INCREASES AS H DECREASES … which means that the monthly and daily flow regime become more irregular as the region is more arid (dependency statistical significant).

  11. Wetter region more regular annual, monthly and daily flow regimes (northern region) Higher values of H Drier region more irregular annual, monthly and daily flow regimes (southern region) Lower values of H Spain Atlantic Ocean Mean annual flow depth PORTUGAL Atlantic Ocean

  12. … mean annual flow depth is able to “TO ASSESS” the relative temporal variability of the flow regime .. therefore it works as aFLOW REGIONALIZATION PARAMETER. • If so, based on H it should be possible to establish ANNUAL, MONTHLY and DAILY FLOW SERIES at UNGAUGED WATERSHEDS (by means of transposition procedures). H as a regionalization parameter … conclusions of the previous analysis • WATERSHEDS with SIMILAR MEAN ANNUAL FLOW DEPTHS, H, exhibit ANNUAL, MONTHLY and DAILY FLOW REGIMES with VERY SIMILAR RELATIVE TEMPORAL VARIABILITY.

  13. Evaluation of flow series at ungauged watersheds (cont.) Validation of the previous conclusions based on the application of the TRANSPOSITION PROCEDURES 1) Gauged watershed,B1, with a mean annual flow depthH1. 2) “Transposition” toB2of the flow series measured atB1. 3)Watershed,B2, fictitiously considered ungauged and having a mean annual flow depthH2close enough toH1. 4)For B2, comparisonof thetransposedflow series with theobser-ved.

  14. Evaluation of flow series at ungauged watersheds (cont.) Transposition of ANNUAL, MONTHLY and DAILY flows FROM … TO … COMPARISON between TRANSPOSED and OBSERVED flows AT …. MONTE DA PONTE (707 km2) ENTRADAS (52 km2) ENTRADAS (52 km2) CIDADELHE (1 685 km2) CASTANHEIRO (3 718 km2) CASTANHEIRO (3 718 km2)

  15. Evaluation of flow series at ungauged watersheds (cont.) Entradas(52 km2) – annual flows transposed from Monte da Ponte ( 707 km2) Transposed flows Observed flows

  16. Evaluation of flow series at ungauged watersheds (cont.) Entradas(52 km2) – monthly flows transposed from Monte da Ponte ( 707 km2) Transposed flows Observed flows

  17. Evaluation of flow series at ungauged watersheds (cont.) Entradas(52 km2) – daily flows transposed from Monte da Ponte ( 707 km2) Wet year Transposed flows Observed flows Observed flows Transposed flows Dry year

  18. Evaluation of flow series at ungauged watersheds (cont.) Entradas(52 km2) – flows transposed from Monte da Ponte ( 707 km2) Observed flows Transposed flows Correlation coefficient, r, between transposed and observed flow series at Entradas (period of 19 years, from 1971/72 to 1989/90): • Annual flows r=0.989 • Monthly flows r=0.986 • Daily flows r=0.893

  19. Evaluation of flow series at ungauged watersheds (cont.) CIDADELHE(1 685 km2) – annual flows transposed from CASTANHEIRO (3 718 km2) Observed flows Transposed flows

  20. Evaluation of flow series at ungauged watersheds (cont.) CIDADELHE(1 685 km2) – monthly flows transposed from CASTANHEIRO (3 718 km2) Observed flows Transposed flows

  21. Evaluation of flow series at ungauged watersheds (cont.) CIDADELHE(1 685 km2) – daily flows transposed from CASTANHEIRO (3 718 km2) Wet year Transposed flows Observed flows Transposed flows Observed flows Dry year

  22. Evaluation of flow series at ungauged watersheds (cont.) CIDADELHE(1 685 km2) – annual flows transposed from CASTANHEIRO (3 718 km2) Observed flows Transposed flows Correlation coefficient, r, between transposed and observed flow series at Cidadelhe (period of 16 years, from 1958/59 to 1973/74): • Annual flows r=0.953 • Monthly flows r=0.937 • Daily flows r=0.865

  23. Evaluation of flow series at ungauged watersheds (cont.) The previous examples clearly show that the yearly, monthly and daily flow at a ungauged watershed can be obtained by transposing the observed flow in the same year, month or day from an gauged watershed. The equations that accomplish the transposition are included in the paper. It must be stressed that the transpositionprocedurerequires that the mean annual flow depths at the ungauged and at the gauged watersheds are close enough in order to ensure flows regimes with similar relative temporal irregularity.

  24. Evaluation of the storage capacities of reservoirs • In countries, like Portugal, with highly irregular flow regimes, the utilization of the water surface resources requires most of the time reservoirs that partially adjust the inflows to the variability of the water demands.

  25. Evaluation of the storage capacities of reservoirs (cont.) Inflow Evaporation Discharge Water supply Net storage capacity, C • The capability of a reservoir to regularize the inflows is ensured by its net storage capacity, C. This capacity depends on several factors such as the characteristics of the inflows (in what concerns their availability and temporal irregularity) and of the supplies (in terms of the required volumes along time) and on the guaranty of the water supplies. • Based on the mean annual flow depth, H, it is also possible to preliminary evaluate of the net storage capacity of reservoirs, C.

  26. Evaluation of the storage capacities of reservoirs (cont.) In fact, the application of simulation algorithms to the exploitation of 54 hypothetical reservoirs showed that the net storage capacity, C, can be related with the mean annual flow depth, H, according to the following general equation, applicable to uniform water demands: where: H mean annual flow depth (mm); G guaranty of the water supply (-); Q function; C net storage capacity of the reservoir (m3); V mean annual flow expressed in volume (m3); C/Vspecific storage capacity of the reservoir (-); Vf annual volume required by an uniform water demand (m3); Vf/Vdegree of the water utilization (-).

  27. Evaluation of the storage capacities of reservoirs (cont.) Based on the previous equation the specific storage capacities, C/V, that ensure different water demands, Vf/V, with different guaranties, G, were estimated, as exemplified in the figure for the guaranty of 90%.

  28. Evaluation of the storage capacities of reservoirs (cont.) By fixing the guaranty, G, and by applying regression analysis to the logarithmic transformed of the mean annual flow depth, H, and of the specific storage capacity, C/V, relationships of the following type were achieved, as represented in the figure for the guaranty of 85%: where l and d are parameters.

  29. Evaluation of the storage capacities of reservoirs (cont.) Parametersl and d and correlation coefficients of the regression analysis, r, for different guaranties, G, and water demands, Vf/V (expressed in terms of the degree of utilization of the mean annual).

  30. Evaluation of the storage capacities of reservoirs (cont.) It should be stressed the high values of the correlation coefficient, r.

  31. Evaluation of the storage capacities of reservoirs (cont.) Thus, it is possible to evaluate the net storage capacity of a reservoir that ensures a given uniform water supply with a given guaranty based only on the mean annual flow depth.

  32. Several studies carried out by the authors showed that the mean annual flow depth, H, is a powerful hydrologic parameter that enables to assess in an easy and enough reliable way the characteristics of the flow regime In Portuguese rivers. • Thus, H can be used as a regionalization parameter that allows establishing the annual, monthly and even daily flows series at ungauged watersheds. • Thus, H can be used as a regionalization parameter that allows establishing the annual, monthly and even daily flows series at ungauged watersheds. • Also based on H it is possible to preliminary evaluate the net storage capacity required by a reservoir in order to supply a given uniform amount of water with a given guaranty. • Also based on H it is possible to preliminary evaluate the net storage capacity required by a reservoir in order to supply a given uniform amount of water with a given guaranty. • Though the procedures referred herein concern to Portugal, the authors believe that they can also be generalized to other European regions having climatic characteristics similar to those of Portugal, with emphasis to the Southern European countries, including Macedonia and some of the surrounding countries. Final remarks • Several studies carried out by the authors showed that the mean annual flow depth, H, is a powerful hydrologic parameter that enables to assess in an easy and enough reliable way the characteristics of the flow regime In Portuguese rivers.

  33. Preliminary design of the storage capacity of reservoirs based on a flow regionalization parameter Maria Manuela PORTELA, Technical University of Lisbon, IST, Portugal mps@civil.ist.utl.pt António de Carvalho QUINTELA, TechnicalUniversity of Lisbon, IST, Portugal acq@civil.ist.utl.pt

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