Abstract
The flood magnitudes with 25, 50, and 100 years return periods and the environmental flows (Qenv) are of outmost importance in the context of hydraulic and hydrologic design. In this study, 25 watershed characteristics were linked with the aforementioned recurrence intervals, peak discharge values, as well as Qenv for 15 pristine torrential watersheds with more than 10 years of streamflow records in the Rhodopi mountain range with a view to generating regional relationships for the assessment of discharge annual peaks and environmental flows regarding the ungauged torrential watersheds in the region. The Log-Pearson Type III probability distribution was fitted in the discharge annual peaks time series, so as to predict Q25, Q50, and Q100, whereas the Tennant method was utilised so as to estimate the environmental flows magnitude. Similarly, the Kolmogorov–Smirnov and the Anderson–Darling tests were performed to verify the distribution fitting. The Principal Components Analysis method reduced the explanatory variables number to 14, whilst the stepwise multiple regression analysis indicated that the exponential model is suitable for predicting the Q25, the power model best forecasted the Q50 and Q100, whereas the linear model is appropriate for Qenv prognosis. In addition, the reliability of the obtained regression models was evaluated by employing the R2, the Nash–Sutcliffe efficiency, and the Index of Agreement Statistical Criteria, which were found to range from 0.91–0.96, 0.88–0.95 and 0.97–0.99, respectively, thereby denoting very strong and accurate forecasts by the generated equations. Thus, the developed equations could successfully predict the peak discharge values and environmental flows within the region’s ungauged watersheds with the drainage size not exceeding 330 km2.
Highlights
Credible peak flows magnitude estimates with 25, 50, and 100 years return periods denote essential pieces of information for the culvert design in forest roads [1], with respect to flood risk hazard assessment studies [2], concrete gravity dams design [3], and many other hydraulic works [4].In gauged watersheds, this information is obtained through the use of flood frequency estimation techniques that were applied in historic peak discharges time series to calculate the likely magnitude of future extreme events through extrapolation [5]
This study confirmed the notion that regionalisation techniques use produces reliable models that are suitable for predicting peak discharge with 25, 50, and 100 years return periods and environmental flows with great accuracy, whereas the latter information is absolutely necessary for water resources management projects, and hydrologic and hydraulic design
The selected 25 watershed characteristics were calculated for 15 pristine watersheds in the region using standard Geographical Information Systems (GIS) methods and they represented the independent model variables, whereas Principal Component Analysis (PCA) analysis reduced the explanatory variables number to 14
Summary
Credible peak flows magnitude estimates with 25, 50, and 100 years return periods denote essential pieces of information for the culvert design in forest roads [1], with respect to flood risk hazard assessment studies [2], concrete gravity dams design [3], and many other hydraulic works [4].In gauged watersheds, this information is obtained through the use of flood frequency estimation techniques that were applied in historic peak discharges time series to calculate the likely magnitude of future extreme events through extrapolation [5]. Credible peak flows magnitude estimates with 25, 50, and 100 years return periods denote essential pieces of information for the culvert design in forest roads [1], with respect to flood risk hazard assessment studies [2], concrete gravity dams design [3], and many other hydraulic works [4]. It is essential to ensure river sustainability, the integrity of associated ecosystems, and the well-being of humans by maintaining a percent of the discharge sufficient in the river so as to allow the river to continue providing all of its services that it provides prior to its hydrologic alteration The latter threshold is called environmental flow (Qenv ), and a global review of the environmental flow assessment methodologies present status revealed the existence of around 207 different methods for computing Qenv , which could be categorized into four groups (hydrological, hydraulic rating, habitat simulation, and holistic methodologies) [11]. Unlike other methods, hydrological methods do not require as much fieldwork [13] and they continue to be the most widely used approaches across the world [11]
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