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Ｉｎ ｔｈｉｓ ｐａｐｅｒ， ｗｅ ｅｓｔｉｍａｔｅｄ ｔｈｅ ｄｅｓｉｇｎ ｓｔｏｒｍ ｆｏｒ ｍｉｘｅｄ ｌｅｖｅｌ⁃１ ａｎｄ ｌｅｖｅｌ⁃２ ｕｒｂａｎ ｄｒａｉｎ ｓｔａｎｄａｒｄｓ ａｃｃｏｒｄｉｎｇ ｔｏ ｄａｔａ ｏｆ ｔｈｅ ｃｏｍｂｉｎａｔｉｏｎ ｏｆ １⁃ｈｏｕｒ ｒａｉｎｓｔｏｒｍ ａｎｄ ６⁃ｈｏｕｒ ｒａｉｎｓｔｏｒｍ （Ｒ１ｈ⁃Ｒ６ｈ）， ｔｈｅ ｃｏｍｂｉｎａｔｉｏｎ ｏｆ １⁃ｈｏｕｒ ｒａｉｎｓｔｏｒｍ ａｎｄ １２⁃ｈｏｕｒ ｒａｉｎｓｔｏｒｍ（Ｒ１ｈ⁃Ｒ１２ｈ）， ａｎｄ ｔｈｅ ｃｏｍｂｉｎａｔｉｏｎ ｏｆ １⁃ｈｏｕｒ ｒａｉｎｓｔｏｒｍ ａｎｄ ２４⁃ｈｏｕｒ ｒａｉｎｓｔｏｒｍ（Ｒ１ｈ⁃Ｒ２４ｈ） ｉｎ Ｚｈｕｈａｉ ｃｉｔｙ ｂｅｔｗｅｅｎ １９８４ ａｎｄ ２０１５． Ｆｉｒｓｔ， ｔｈｅ ｍｏｄｅｌｓ ｏｆ ｊｏｉｎｔ ｐｒｏｂａｂｉｌｉｔｙ ｄｉｓｔｒｉｂｕｔｉｏｎ ａｂｏｕｔ ｄｉｆｆｅｒｅｎｔ ｃｏｍｂｉｎａｔｉｏｎｓ ｗｅｒｅ ｂｕｉｌｔ ｕｓｉｎｇ ｔｈｅ Ａｒｃｈｉｍｅｄｅａｎ ｅｘｔｒｅｍｅ ｖａｌｕｅ Ｃｏｐｕｌａ ａｎｄ ｔｈｅ Ｋｅｎｄａｌｌ ｄｉｓｔｒｉｂｕｔｉｏｎ ｆｕｎｃｔｉｏｎ． Ｔｈｅｎ， ｔｈｅ ｏｃｃｕｒｒｅｎｃｅ ｐｒｏｂａｂｉｌｉｔｙ， "ＯＲ" ｒｅｔｕｒｎ ｐｅｒｉｏｄ， "ＡＮＤ" ｒｅｔｕｒｎ ｐｅｒｉｏｄ ａｎｄ ｔｈｅ ｓｅｃｏｎｄａｒｙ ｒｅｔｕｒｎ ｐｅｒｉｏｄ ｆｏｒ ｅａｃｈ ｃｏｍｂｉｎａｔｉｏｎ ｗｅｒｅ ａｎａｌｙｚｅｄ， ａｎｄ ｔｈｅ ｄｅｓｉｇｎ ｓｔｏｒｍｓ ｆｏｒ ｅａｃｈ ｃｏｍｂｉｎａｔｉｏｎ ｗｅｒｅ ｅｓｔｉｍａｔｅｄ ｂｙ ｔｈｅ ｍｅｔｈｏｄ ｗｉｔｈ ｔｈｅ ｍａｘｉｍｕｍ ｏｃｃｕｒｒｅｎｃｅ ｐｒｏｂａｂｉｌｉｔｙ． Ｔｈｅ ｒｅｓｕｌｔｓ ａｒｅ ａｓ ｆｏｌｌｏｗｓ： ｔｈｅ ｃｕｍｕｌａｔｉｖｅ ｆｒｅｑｕｅｎｃｙ ｃｏｒｒｅｓｐｏｎｄｉｎｇ ｔｈｅ ｓｅｃｏｎｄａｒｙ ｒｅｔｕｒｎ ｐｅｒｉｏｄ ｍｏｒｅ ａｃｃｕｒａｔｅｌｙ ｒｅｐｒｅｓｅｎｔｓ ｔｈｅ ｒｉｓｋ ｐｒｏｂａｂｉｌｉｔｉｅｓ ｏｆ ｒａｉｎｓｔｏｒｍｓ ｏｆ ｄｉｆｆｅｒｅｎｔ ｃｏｍｂｉｎａｔｉｏｎｓ ｗｉｔｈ ｓｐｅｃｉｆｉｃ ｄｅｓｉｇｎ ｆｒｅｑｕｅｎｃｙ； ｔｈｅ ｅｓｔｉｍａｔｅｄ ｄｅｓｉｇｎ ｓｔｏｒｍ ｑｕａｎｔｉｌｅｓ ｏｆ ｔｈｅ ｓｅｃｏｎｄａｒｙ ｒｅｔｕｒｎ ｐｅｒｉｏｄ ｂａｓｅｄ ｏｎ ｒｅｔｕｒｎ ｐｅｒｉｏｄｓ ｗｉｔｈ ２⁃ｙｅａｒ， ３⁃ｙｅａｒ， ５⁃ｙｅａｒ， １０⁃ｙｅａｒ， ２０⁃ｙｅａｒ， ５０⁃ｙｅａｒ ａｎｄ １００⁃ｙｅａｒ ａｒｅ ｂｅｔｗｅｅｎ ｔｈｅ ｄｅｓｉｇｎ ｓｔｏｒｍ ｑｕａｎｔｉｌｅｓ ｏｆ ｔｈｅ "ＯＲ" ｒｅｔｕｒｎ ｐｅｒｉｏｄ ａｎｄ ｔｈｅｓｅ ｏｆ ｔｈｅ "ＡＮＤ" ｒｅｔｕｒｎ ｐｅｒｉｏｄ， ａｎｄ ｌｅｓｓ ｔｈａｎ ｔｈｅｓｅ ｏｆ ｔｈｅ ｍａｒｇｉｎａｌ ｄｉｓｔｒｉｂｕｔｉｏｎ ｒｅｔｕｒｎ ｐｅｒｉｏｄ， ｒｅｓｐｅｃｔｉｖｅｌｙ． Ｃｏｍｐａｒｅｄ ｗｉｔｈ ｔｈｅ ｃａｓｅ ｏｆ ｄｅｓｉｇｎ ｓｔｏｒｍ ｑｕａｎｔｉｌｅｓ ｏｆ ｔｈｅ ｍａｒｇｉｎａｌ ｄｉｓｔｒｉｂｕｔｉｏｎ ｒｅｔｕｒｎ ｐｅｒｉｏｄ， ｔｈｅ ｒｅｌａｔｉｖｅ ｅｒｒｏｒ ｏｆ ｔｈｅ Ｒ１ｈ⁃Ｒ６ｈ ｉｓ ｂｅｔｗｅｅｎ ３.１％ ａｎｄ ７.１％； ｔｈａｔ ｏｆ ｔｈｅ ｃｏｍｂｉｎａｔｉｏｎ ｏｆ Ｒ１ｈ⁃Ｒ１２ｈ ｉｓ ｂｅｔｗｅｅｎ ３.３％ ａｎｄ ９.３％； ｔｈａｔ ｏｆ Ｒ１ｈ⁃Ｒ２４ｈ ｉｓ ｂｅｔｗｅｅｎ ３.９５％ ａｎｄ １２.０％． Ｔｈｅｓｅ ｐｒｏｖｉｄｅ ｏｐｔｉｍｉｚａｔｉｏｎ ｃｒｉｔｅｒｉｏｎ ａｎｄ ｇｕｉｄｅ ｆｏｒ ｔｈｅ ｒｉｓｋ ｍａｎａｇｅｍｅｎｔ ｏｆ ｗａｔｅｒｌｏｇｇｉｎｇ ｐｒｏｊｅｃｔ ａｎｄ ｔｈｅ ｄｅｓｉｇｎ ｏｆ ｄｒａｉｎａｇｅ ｐｉｐｅ， ｒｅｓｐｅｃｔｉｖｅｌｙ． [ABSTRACT FROM AUTHOR]

To avoid the nuisance of frequent flooding during rainy season, designing an efficient stormwater drainage system has become the need of the hour for present world engineers and urban planners. The present case study deals with providing a solution to stormwater management problem in an urbanized area. Mann-Kendall and Sen's slope tests are used to perform the trend analysis of rainfall events using daily rainfall data (1956-2012), while the L-moments-based frequency analysis method is employed to estimate the design storm for a small urbanized area in West Bengal, India, using daily annual maximum rainfall (1975-2013). SWMM (Storm Water Management Model) and MIKE URBAN models are used to design an efficient drainage system for the study area. Two-dimensional (2D) MIKE URBAN model is primarily used to overcome the limitation of one-dimensional (1D) SWMM in simulating flood extent and flood inundation. Model simulation results from MIKE URBAN are shown for an extreme rainfall event of July 29, 2013. A multi-purpose detention pond is also designed for groundwater recharge and attenuating the peak of outflow hydrograph at the downstream end during high-intensity rainfall. This study provides an insight into the importance of 2D model to deal with location-specific flooding problems. [ABSTRACT FROM AUTHOR]

Managing stormwater under climate uncertainty is a concern in both built-out communities and those continuing to undergo land use change. In this study, a suite of climate change scenarios were developed to represent a probable range of change in the 10-year recurrence interval design storm. The Environmental Protection Agency's Stormwater Management Model was used to predict flooding due to undersized drainage components within watersheds representing a traditional, built-out urban area and a developing suburban area with intact green infrastructure corridors. Despite undersized infrastructure and flooding in both study watersheds, the risk of property damage in the suburban watershed was negligible across the range of scenarios even at projected build-out, due in part to flood storage capacity of the green infrastructure network. Adaptation approaches - including pipe upsizing, underground storage, and bioinfiltration - and costs were also modeled in both watersheds. In the built-out site, bioinfiltration practices were predicted to moderate both flooding and total adaptation costs even when implemented over a relatively modest (10 %) portion of the watershed; however, a substantial upgrade to gray stormwater infrastructure (pipes and storage chambers) was also needed to mitigate impacts. In the urbanizing community, maintaining an intact green infrastructure network was surmised to be the most cost-effective approach for enhancing the resilience of urban stormwater systems to climate uncertainties and urbanization. [ABSTRACT FROM AUTHOR]

As small scale green infrastructures, rain gardens have been widely advocated for urban stormwater management in the contemporary low impact development (LID) era. This paper presents a simple method that consists of hydrological models and the matching plots of nomographs to provide an informative and practical tool for rain garden sizing and hydrological evaluation. The proposed method considers design storms, infiltration rates and the runoff contribution area ratio of the rain garden, allowing users to size a rain garden for a specific site with hydrological reference and predict overflow of the rain garden under different storms. The nomographs provide a visual presentation on the sensitivity of different design parameters. Subsequent application of the proposed method to a case study conducted in a sub-humid region in China showed that, the method accurately predicted the design storms for the existing rain garden, the predicted overflows under large storm events were within 13–50% of the measured volumes. The results suggest that the nomographs approach is a practical tool for quick selection or assessment of design options that incorporate key hydrological parameters of rain gardens or other infiltration type green infrastructure. The graphic approach as displayed by the nomographs allow urban planners to demonstrate the hydrological effect of small scale green infrastructure and gain more support for promoting low impact development. [ABSTRACT FROM AUTHOR]

Representation of precipitation is one of the most difficult aspects of modelling post-fire runoff and erosion and also one of the most sensitive input parameters to rainfall-runoff models. The impact of post-fire convective rainstorms, especially in semiarid watersheds, depends on the overlap between locations of high-intensity rainfall and areas of high-severity burns. One of the most useful applications of models in post-fire situations is risk assessment to quantify peak flow and identify areas at high risk of flooding and erosion. This study used the KINEROS2/AGWA model to compare several spatial and temporal rainfall representations of post-fire rainfall-runoff events to determine the effect of differing representations on modelled peak flow and determine at-risk locations within a watershed. Post-fire rainfallrunoff events at Zion National Park in Utah and Bandelier National Monument in New Mexico were modelled. Representations considered included both uniform and Soil Conservation Service Type II hyetographs, applying rain over the entire watershed and applying rain only on the burned area, and varying rainfall both temporally and spatially according to radar data. Results showed that rainfall representation greatly affected modelled peak flow, but did not significantly alter the model's predictions for high-risk locations. This has important implications for post-fire assessments before a flood-inducing rainfall event, or for post-storm assessments in areas with low-gauge density or lack of radar data due to mountain beam blockage. [ABSTRACT FROM AUTHOR]

• Surrogates obtained by machine learning are used to optimize areas of low impact development practices. • Backpropagation neural network outperforms multiple linear regression and generalized regression neural network in predicting the volume and peak rate of catchment outflow. • The computational load of surrogate-based optimization is far less than the storm water management model. The optimal implementation of low impact development (LID) practices remains an open research issue. Multiobjective optimization (MOO) based on physically-based models facilitates LID sizing but requires large computational budgets. We developed and validated a surrogate MOO framework based on machine learning (ML) models to obtain satisfactory optimal solutions with an affordable computational cost. First, a calibrated and validated storm water management model (SWMM) was driven by a 2-year, 120 min Chicago pattern storm with random LID areas for generating 10,000 samples. Second, ML models, including multiple linear regression (MLR), generalized regression neural network (GRNN), and backpropagation neural network (BPNN), were trained and validated to predict catchment total outflow (CTO) and catchment peak outflow (CPO). Third, using the outperformed ML models as surrogates, the LID areas were optimized by non-dominated sorting genetic algorithm-II to minimize construction costs, CTO, and CPO. The results obtained for an urban catchment in Fengxi, China, demonstrated that: (1) BPNN outperformed MLR and GRNN in terms of accuracy, while the training time (∼40 min) was ∼6857 times and ∼706 times that of MLR (∼0.35 s) and GRNN (3.4 s) models, respectively. (2) The optimization process using BPNN models as surrogates converged well, indicating the efficiency of the proposed framework. (3) Under the marginal effect, the permeable pavement was identified as the leading practice for most Pareto solutions, followed by bioretention cell and green roof. Moreover, a subcatchment with a higher runoff coefficient was deemed preferable for LID implementation. (4) Outflow reduction by the LIDs was significant (CTO and CPO were reduced by 28.6–56.9 % and 27.5–48.3 %, respectively) but negligible for retarding the time of CPO. (5) The optimization time was reduced by ∼95.82 % using the surrogate-based MOO instead of the SWMM-based model when the training time of the BPNN models was ignored. This study provides insights into the efficient optimization of LIDs. [ABSTRACT FROM AUTHOR]

Recognized as an effective low impact development (LID) practice, rain gardens have been widely advocated to be built with urban landscaping for stormwater runoff reduction through the retention and infiltration processes; but the field performance and regional effect of rain gardens have not been thoroughly investigated. In this paper, we presented a four-year monitoring study on the performance of a rain garden on stormwater retention; hydrological models were proposed to predict the potential effect of rain gardens on runoff reduction under different storms and the future urban development scenarios. The experimental rain garden was constructed in a sub-humid loess region in Xi'an, China; it has a contributing area ratio of 20:1 and depth of 15 cm. During the study period, we observed 28 large storm events, but only 5 of them caused overflow from the rain garden. The flow reduction rate for the overflow events ranged from 77 to 94 %. The runoff coefficient from the contributing area ( RC) was reduced to less than 0.02 on annual basis, and 0.008 over the four years average. Field observations also showed that infiltration rate remained stable during the operation period. The predictions based on the future landuse and storm variability of the study area showed that by converting a small fraction of the city land area into rain gardens, the negative hydrological effect from expansion of impervious area can be reduced significantly. The challenge, however, lies in how to plan and build rain gardens as an integral part of the urban landscape. [ABSTRACT FROM AUTHOR]

Rainfall accumulation depths over a given area are strongly dependent on the shape of the storm together with its direction of advection. A method to produce design storms exhibiting anisotropic spatial scaling is presented by combining a state-of-the-art stochastic rainfall generator STEPS with the linear generalized scale invariance (GSI) notation. The enhanced model is used to create ensembles of design storms based on an extreme storm with a distinct rainband shape observed in Melbourne, Australia. Design storms are generated both with and without accounting for anisotropy. Effect of anisotropy on precipitation characteristics is studied using the entire region covered by the radar ( radar scale) and at a significantly smaller catchment scale. A rainfall-runoff model is applied to route the rainfall through the catchment into streamflow. Accounting for anisotropy allows for a more realistic description of precipitation features at the radar scale. At the catchment scale, anisotropy increases the probability of high rainfall accumulations, which translates into greater flood volumes. No discernible difference was observed in streamflow characteristics after controlling for the accumulation over the catchment. This could be explained by a lower importance of anisotropy relative to other factors affecting streamflow generation, and by the difficulties in creating representative rainfall temporal properties at the catchment scale when the radar scale is used for model calibration. The proposed method provides a tool to create ensembles of design storms when the anisotropic shape of the fields is of importance. [ABSTRACT FROM AUTHOR]

In recent years, due to global climate change and rapid urbanization, extreme weather events occur to the city at an increasing frequency. Waterlogging is common because of heavy rains. In this case, the urban drainage system can no longer meet the original design requirements, resulting in traffic jams and even paralysis and post a threat to urban safety. Therefore, it provides a necessary foundation for urban drainage planning and design to accurately assess the capacity of the drainage system and correctly simulate the transport effect of drainage network and the carrying capacity of drainage facilities. This study adopts InfoWorks Integrated Catchment Management (ICM) to present the two combined sewer drainage systems in Yangpu District, Shanghai (China). The model can assist the design of the drainage system. Model calibration is performed based on the historical rainfall events. The calibrated model is used for the assessment of the outlet drainage and pipe loads for the storm scenario currently existing or possibly occurring in the future. The study found that the simulation and analysis results of the drainage system model were reliable. They could fully reflect the service performance of the drainage system in the study area and provide decision-making support for regional flood control and transformation of pipeline network. [ABSTRACT FROM AUTHOR]

The time distribution of rainfall is an important input to rainfall-runoff modelling and has a significant effect on the resulting peak discharge. At many facilities in the oil sands region of Alberta, the Natural Resources Conservation Service (NRCS) Type II design storm has typically been used for design of surface water management facilities. The appropriateness of the Type II design storm and several other time distributions was assessed by comparing the modelled peak runoff from the design storms with the modelled runoff from historical 24-h rainfall events in five small typical catchments. Results indicate that the NRCS Type II produces highly conservative runoff peaks compared to actual rainfall events at Fort McMurray, and a new synthetic design storm developed during the study more closely parallels the peak runoff produced by actual rainfall events. [ABSTRACT FROM AUTHOR]

This paper presents the derivation of the design storm hyetograph patterns for the Kingdom of Saudi Arabia based on real rainfall events from meteorological stations distributed throughout the Kingdom. Two thousand twenty-seven rainfall storms for a 20-28-year period were collected and analyzed covering 13 regions of the Kingdom. Four distinct dimensionless rainfall hyetograph patterns have been obtained over the Kingdom, while two patterns have been obtained for each individual region because of the lack of data for long-duration storms in individual regions. The resulting dimensionless rainfall patterns for each region can be used to develop storm hyetographs for any design duration, total rainfall depth and return period. It has been shown that the developed storm hyetographs have different features from other storm patterns that are commonly used in arid zones. The study recommends using these curves for the design of hydraulic structures in Kingdom of Saudi Arabia and regions alike. [ABSTRACT FROM AUTHOR]

Highlights: [•] An efficient and robust method for the estimation of the annual flood frequency distribution is developed. [•] It combines the advantages of the continuous simulation and event-based methods, i.e., accuracy and efficiency. [•] The joint probability nature of the rainfall-runoff process is taken into account and the AEP neutrality assumption is avoided. [•] It approach uses the causative events of the streamflows to derive the annual flood distribution. [•] It reduces computational demand compared with a long continuous simulation. [ABSTRACT FROM AUTHOR]

Abstract: Low impact development (LID) is generally regarded as a more sustainable solution for urban stormwater management than conventional urban drainage systems. However, its effects on urban flooding at a scale of urban drainage systems have not been fully understood particularly when different rainfall characteristics are considered. In this paper, using an urbanizing catchment in China as a case study, the effects of three LID techniques (swale, permeable pavement and green roof) on urban flooding are analyzed and compared with the conventional drainage system design. A range of storm events with different rainfall amounts, durations and locations of peak intensity are considered for holistic assessment of the LID techniques. The effects are measured by the total flood volume reduction during a storm event compared to the conventional drainage system design. The results obtained indicate that all three LID scenarios are more effective in flood reduction during heavier and shorter storm events. Their performance, however, varies significantly according to the location of peak intensity. That is, swales perform best during a storm event with an early peak, permeable pavements perform best with a middle peak, and green roofs perform best with a late peak, respectively. The trends of flood reduction can be explained using a newly proposed water balance method, i.e., by comparing the effective storage depth of the LID designs with the accumulative rainfall amounts at the beginning and end of flooding in the conventional drainage system. This paper provides an insight into the performance of LID designs under different rainfall characteristics, which is essential for effective urban flood management. [Copyright &y& Elsevier]

Adequate consideration of the joint problems of natural channel stability and biocommunity preservation in greenfield catchments experiencing development has been lacking in the WSUD (water sensitive urban design) guidelines promoted in eastern and southern Australia in recent years. The paper offers retention technology as a vital ingredient of catchment management, enabling urbanisation to proceed with minimum loss of waterway environmental values. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this paper is to develop an empirical formula to estimate design rainfall intensity based on intensity–duration–frequency (IDF) curves. These curves have been generated from a 32-year recorded rainfall data for Riyadh region. Rainfall intensity–duration–frequency curves describe rainfall intensity as a function of duration for a given return period which are important for the design of storm water drainage systems and hydraulic structures. The formula is derived using the analysis of results of three different frequency methods, namely: Gumbel, Log Pearson III, and Log normal. These methods are used to obtain the IDF curves for six different durations (10, 20, 30min, and 1, 2, 24h) and six frequency periods (2, 5, 10, 25, 50, 100years) where the best method of IDF estimation is recommended for future analysis. The equation can predict rainfall intensity in Riyadh region for any return period with a given storm duration and calibrated parameters obtained from IDF curves. Good match was achieved between its results and other analytical methods results such as Gumbel method. Moreover, it allows incorporating data from non-recording stations, thus remedying the problem of establishing IDF curves in places with a sparse network of rain-recording stations. [Copyright &y& Elsevier]

The objective of this study was to investigate the presence of trends in extreme precipitation (denoted MAXP and defined as the annual maximum daily precipitation depth) time series for coastal northern New England and to assess changes in the magnitude of the so-called 100-year storm. MAXP depths from 48 stations with long, continuous records in Maine, New Hampshire, and Massachusetts were analyzed. At those same stations, the number of daily precipitation depths ≥2 in. (51 mm, denoted as GT2in) was also quantified for each year. Although the seasonally averaged MAXP was found to be fairly uniform throughout the year, the frequency of MAXP is highest during August through October, the typical hurricane season in New England. The presence of trends in MAXP and GT2in was evaluated over four time frames (1954-2005, 1954-2008, 1970-2005, and 1970-2008) using two statistical methods (linear regression and the Mann-Kendall trend test) and at two scales (at-site and regional). The trend analysis over the time period 1954-2005 indicated that MAXP was amazingly stationary; however, a trend in GT2in was found at some stations. More trends in both MAXP and GT2in were present in the time period 1954-2008. The majority of stations in southern New Hampshire and eastern Massachusetts showed evidence of trends in MAXP (but not GT2in) for the time period 1970-2008. That the number of trends in MAXP increased despite the shorter record length suggests a strong increase in the magnitude of extreme precipitation in northern coastal New England in the last few decades. The stationarity of the 1954-2005 record was confirmed by the regional trend analysis, as was the presence of stronger trends in coastal stations when the record was extended through 2008. Most stations that had trends in MAXP also had trends in GT2in. The generalized extreme value (GEV) distribution was used to estimate 100-year precipitation depth quantiles for the 1954-2005 record, which were then compared with Technical Paper No. 40 (TP-40) 100-year, 24-h precipitation depths. Estimates for stations along coastal Massachusetts, New Hampshire, and Maine all exceeded 7 in. (180 mm) and exceeded TP-40 by 1 in. (25 mm) or more. Stations in northeastern Massachusetts, southeastern New Hampshire, and southern Maine exceeded 8 in. (200 mm) and also exceeded TP-40 estimates by more than 2 in. (51 mm). These findings indicate that TP-40 underrepresents coastal storm depths. This study, as well as recent record-breaking events in northern New England, strongly suggests the need for updating of design storm estimates. Furthermore, extreme precipitation events of longer than one-day duration have caused large-scale flooding in the region over the last decade. The magnitude of longer duration storms (particularly two-day storms) may also be increasing, calling for engineered infrastructure that can accommodate increases in both storm magnitude and duration. [ABSTRACT FROM AUTHOR]

This article presents the elements involved in the design of a bioretention planter/trench infiltration-detention system as part of a very large-scale urban retrofit project. The prototype system was designed to intercept all of the runoff from a synthetic 5.08-mm 24-h rainfall event. Diverted flows were conveyed into bioretention planter for treatment. The bioretention systems were fingerprinted into areas comprising 0.8% of the contributory drainage areas, with an associated stone trench comprising another 3.4%. As layered systems, an approach that is capable of modeling vertical flows in addition to dynamic routing of outflows is used. The system was first modeled using HydroCAD, a design storm event modeling software. A four-compartment node system is used to model the dynamics of flow through the layers. The system was then modeled using SWMM 5.0.014 continuous simulation software. The resulting response to a design storm was computed by both of these models to compare the results of each method. The resulting SWMM model was then run on the 2005 design year rainfall distribution. Under existing conditions, over 60% of annual runoff volume exceeded the 3.50 L·s-1·ha-1(0.05 cfs-ac-1) threshold for initiation of combined sewer overflows (CSOs). Nearly all runoff was intercepted by the planter/trench infiltration system and even with a soil infiltration rate of only 2.54 mm·h-1, 47% was infiltrated, and less than 6% was discharged at rates that could initiate CSOs. The number of CSO exceedance pulses was reduced from 233 to 6, a reduction of 97%. The volume of flows exceeding the CSO threshold decreased by 90% in the planter/trench system. [ABSTRACT FROM AUTHOR]

Summary: This study extends the concept of the regional envelope curve (REC) of flood flows to extreme rainstorm events by introducing the Depth-Duration Envelope Curves (DDEC). DDEC are defined as regional upper bounds on observed rainfall maxima for several rainfall durations. The study adapts the probabilistic interpretation recently proposed for REC, which enables one to estimate the recurrence interval T of the curve, to DDEC. The study also assesses the suitability of DDEC for estimating the T-year rainfall event associated with a given duration and large T values. We illustrate an application of DDEC to annual maximum series of rainfall depth with duration spanning from 15min to 24h collected at 208 raingauges located in northern-central Italy. The accuracy of rainfall quantiles retrieved for ungauged sites from DDEC is assessed through a comparison with a Regional Depth-Duration-Frequency Equation that was recently proposed for the same study area. [Copyright &y& Elsevier]

Sustainable development means to protect and improve environment for future generation use. An effective protection requires action to limit global warming prevention catastrophic phenomena, such as severe floods or long-term droughts, and safeguarding people from their effects. Analyzing these phenomena evolution, the Romanian specialized institutes have adopted a new approach and developed a modem strategy, based on the latest hydrological theory available worldwide. According to this strategy, the Romanian authorities have begun to develop and implement new norms and technical regulations. These norms and technical regulations have fully changed the previous approach of the storm and runoff modelling in Romania. The paper presents the modeling methods of the design storm and overland runoff, which have been the base of the new norms and regulations (Romanian Standard SR 1846-2/2006, "National medium and long-term flood risk management strategy", "Methodology for the establishment of the hydrographic basins exposed to floods") and points out their implications in the environmental protection, water management field and in the fight against extreme meteorological Phenomena such as severe floods and droughts. [ABSTRACT FROM AUTHOR]

After only a few years of operation, an extensive rain gauge network provides fruitful information on temporal patterns of local storms, helping urban water, managers with in the difficult choice of appropriate design storms. A total of 1470 1-h storms were identified for the period 1999-2005 in Québec City based on rainfall depth and interevent time criteria. Taking advantage of a clustering technique, the Kohonen neural network, 1-h storms were divided into 16 clusters depending on similarities in their temporal patterns, and then lumped into four groups. The database revealed that about one-third of all storms have a uniform intensity, one-third are early-peaking, and one-third are either symmetrical or late-peaking. Early-peaking patterns include the highest maximal 5-min intensity: 0.22-0.30 of the rainfall depth range, therefore in the same range as common Canadian 10-year design storms. [ABSTRACT FROM AUTHOR]

Summary: This study focuses mainly on increases in peak discharges with reductions in recurrence intervals for design hydrographs due to growing imperviousness. Rainfall–runoff simulation is a major basis for analyzing the hydrological effects of urbanization. Available recordings of 50 rainfall–runoff events during 1966–2002 were used as the study sample. Forty events were calibrated to determine the relationships between impervious areas and hydrological parameters in the Nash and SCS models. Block Kriging and non-linear programming methods were used to estimate the mean rainfall and its hourly excess value, respectively. The remaining 10 cases were used to test the established relationships. Calibration and verification results confirm that the methods used in this study effectively illustrate the hydrological and geomorphic conditions in complex urbanization processes. The rainfall–runoff routings, by using the design storm approach and the established relationships, demonstrated the following: (1) peak flows of the design flood hydrographs increased by about 127, 266, 375, 440, 515, 564, 593, and 629m3/s for eight return periods, respectively; (2) peak times were individually shortened from 9 to 6h due to urbanization; (3) the recurrence intervals of 200, 100, 50, and 25 years before urbanization were reduced to about 88, 33, 16, and 8 years also due to urbanization if they would have occurred at the present time within the Wu–Tu watershed. Finally, these analytical results can be obtained easily from the designed diagram that shows the relationships among peak discharges, impervious areas and return periods. This research can be used to prevent disasters, loss of life and property damage. [Copyright &y& Elsevier]

Summary: A study was conducted on the effectiveness of green roofs to mitigate stormwater using computer simulation. In this study, the stormwater performance was simulated for a modular block green roof using a packaged soil moisture simulation, HYDRUS-1D, with simulation results verified by study site data. Simulations were run using HYDRUS-1D for 24-h design storms to determine peak flow, retention and detention time for runoff. Storm data collected as part of a green roof study in Athens, Georgia, USA were used to validate HYDRUS-simulated runoff. The study site consisted of a 37m2 (400ft2) modular block green roof containing engineered soil and vegetation including several Sedum species. The study revealed that rainfall depth per storm strongly influences the performance of green roofs for stormwater mitigation, providing complete retention of small storms (<2.54cm) and detention for larger storms, assuming the measured average moisture content (∼10%) as the antecedent condition. [Copyright &y& Elsevier]

Summary: With water shortages occurring in semi-arid areas of the world, the need for multipurpose reservoirs that can, under the requirement of reservoir safety, store sufficient water for supply during dry seasons is becoming egregious. In order to increase water storage of a reservoir while maintaining its security for flood control, two approaches, multiple duration limited water level and dynamic limited water level, are proposed in this study. Contrary to traditional annual limited water level, multiple duration limited water level employs a multiple duration design storm. When a large storm takes place in the first part of multiple duration, the likelihood of another large storm to be occurring in the next part of the duration diminishes. Based on this intuitive reasoning, this study proposes a dynamic limited water level for flood control based on conditional probabilities of large storms. In order to obtain these conditional probabilities, a multivariate autoregressive model with lag one [AR(1)] is chosen for extending multiple duration rainfall series. Using Menlou drainage area in China as an example, multiple duration limited water level and dynamic limited water level for flood control are applied and their benefits for water supply are discussed. [Copyright &y& Elsevier]

The design storm depth is defined as the rainfall depth that is expected to occur in the considered site for a given probability of occurrence and a given duration of the storm. It is generally estimated by using parametric depth-duration-frequency (DDF) equations. In particular, this article considers the frequent case when one needs to estimate the design storm depth for very short durations (typically from 5 to 45 min) while observed rainfall extremes for calibrating the DDF parameters are only available for longer durations. In this case the DDF curves are generally extrapolated below the range of durations that were used for estimating their parameters. It is well known that this procedure induces estimation errors that depend on the type of DDF equation that is used. The aim of this study is to test the capability of seven different DDF curves characterized by two or three parameters to provide an estimate of the design rainfall for storm durations shorter than 1 hour, when their parameterization is performed by using data referred to longer storms. The results point out that a proper choice of the DDF curve may improve the reliability of the design storm depth estimation significantly. In particular, DDF curves with three parameters provide a conservative estimation with an average relative error which never exceeded 20% for all the storm duration considered here. [ABSTRACT FROM AUTHOR]

Climate change raises many concerns for urban water management because of the effects on all aspects of the hydrological cycle. Urban water infrastructure has traditionally been designed using historical observations and assuming stationary climatic conditions. The capability of this infrastructure, whether for storm-water drainage, or water supply, may be over- or under-designed for future climatic conditions. In particular, changes in the frequency and intensity of extreme rainfall events will have the most acute effect on storm-water drainage systems. Therefore, it is necessary to take future climatic conditions into consideration in engineering designs in order to enhance water infrastructure investment planning practices in a long time horizon. This paper provides the initial results of a study that is examining ways to enhance urban infrastructure investment planning practices against changes in hydrologic regimes for s changing climate. Design storms and intensity - duration -frequency curves that are used in the engineering design of storm-water drainage systems are developed under future climatic conditions by empirically adjusting the general circulation model output, and using the Gumbel distribution and the Chicago method. Simulations are then performed on an existing storm-water drainage system from NE Calgary to investigate the resiliency of the system under climate change. [ABSTRACT FROM AUTHOR]

The two-parameter gamma function (G2P) design storm is a recent methodology used to obtain synthetic hyetographs especially developed for urban hydrology applications. Further analytical developments on the G2P design storm are presented herein, linking the rainfall convectivity n-index with the shape parameter of the design storm. This step can provide a useful basis for future easy-to-handle rainfall inputs in the context of regional urban drainage studies. A practical application is presented herein for the case of Valencia (Spain), based on high-resolution time series of rainfall intensity. The resulting design storm captures certain internal statistics and features observed in the fine-scale rainfall intensity historical records. On the other hand, a direct, simple method is formulated to derivate the design storm from the intensity–duration–frequency (IDF) curves, making use of the analytical relationship with the n-index. [ABSTRACT FROM AUTHOR]

Climate change can affect different drivers of flooding in low-lying coastal areas of the world, challenging the design and planning of communities and infrastructure. The concurrent occurrence of multiple flood drivers such as high river flows and extreme sea levels can aggravate such impacts and result in catastrophic damages. In this study, the individual and compound effects of riverine and coastal flooding are investigated at Stephenville Crossing located in the coastal-estuarine region of Newfoundland and Labrador (NL), Canada. The impacts of climate change on flood extents and depths and the uncertainties associated with temporal patterns of storms, intensity–duration–frequency (IDF) projections, spatial resolution, and emission scenarios are assessed. A hydrologic model and a 2D hydraulic model are set up and calibrated to simulate the flood inundation for the historical (1976–2005) as well as the near future (2041–2070) and far future (2071–2100) periods under Representative Concentration Pathways (RCPs) 4.5 and 8.5. Future storm events are generated based on projected IDF curves from convection-permitting Weather Research and Forecasting (WRF) climate model simulations, using SCS, Huff, and alternating block design storm methods. The results are compared with simulations based on projected IDF curves derived from statistically downscaled Global Climate Models (GCMs). Both drivers of flooding are projected to intensify in the future, resulting in higher risks of flooding in the study area. Compound riverine and coastal flooding results in more severe inundation, affecting the communities on the coastline and the estuary area. Results show that the uncertainties associated with storm hyetographs are considerable, which indicate the importance of accurate representation of storm patterns. Further, simulations based on projected WRF-IDF curves show higher risks of flooding compared to the ones associated with GCM-IDFs. [ABSTRACT FROM AUTHOR]

Maximum precipitation, which varies among locations and annually at a location of interest, is the base for sizing hydraulic structures. Understanding such spatiotemporal variations is necessary for accurate rainfall prediction but remains incomplete in most regions, including the state of Virginia. The objective of this study was to fill this information gap for Virginia using 15-min precipitation data collected at 57 gauges. In this regard, a linear regression method and a modified Mann-Kendall technique that can consider the climate-relevant non-stationarity were applied to detect possible step changes and temporal trends of maximum annual rainfall intensities at various time intervals, while spatial statistics, namely global Moran's I and local indicator of spatial association, were used to reveal the spatial autocorrelations and clusters. The results indicated that although no step changes were detected, statistically significant trends were detected for almost half of the selected gauges. The coastal plain experienced an increasing trend in rainfall intensity for durations of 24 h and longer, whereas the other areas of the state had a decreasing trend, with relatively more trends and larger decreasing rates in the west-central ridge-valley areas. The spatial autocorrelations of rainfall intensities in the state of Virginia were dependent on a spatial scale of interest. Given the diversity of the climatic patterns and physiographic features in the testbed, this study demonstrates innovations in understanding how extreme rainfall intensity would be changed from climate change beyond Virginia. • Presented an approach for detecting spatiotemporal variations and spatial autocorrelations of maximum rainfall intensity. • Applied the approach to a U.S. territory that has multivariate climatic and physiographic features (CPFs). • Revealed increasing rainfall intensity in the coastal area and decreasing intensity in the ridge-valley region. • Showed a positive autocorrelation across a geographical area within which the CPFs combinations are uniform. • Showed that such a positive autocorrelation in a larger area tended to be weaker than that in a smaller area. [ABSTRACT FROM AUTHOR]