Significant Impacts of Rainfall Redistribution through the Roof of Buildings on Urban Hydrology

Microtopography on a building roof will direct rainfall from roofs to the ground through downspouts and transform the rainfall spatial distribution from plane to points. However, the issues on whether and how the building-induced rainfall redistribution (BIRR) influences hydrologic responses are still not well understood despite the numerous downspouts in the urban area. Hence, this study brings the roof layer into a grid-based urban hydrologic model (gUHM) to quantitatively evaluate the impacts of BIRR, aiming to enhance the understanding of building effects in urban hydrology and subsequently to identify the necessity of incorporating BIRR into flood forecasting. Nine land development strategies and 27 rainfall conditions are considered herein to characterize the changing circumstance. Results indicate that the impacts of BIRR depend on multiple circumstance factors and are nonnegligible in urban hydrology. The BIRR causes not only bidirectional impacts on the hydrologic characteristic values (e.g., peak flow and runoff volume) but also an obvious alteration of the hydrograph. Overall, the BIRR tends to increase the peak flow, and more importantly, the impact will be aggravated by the increase of rainfall intensity with the maximum relative error of peak flow approaching 10%. This study contributes to a better understanding of building effects on urban hydrology and a step forward to reduce the uncertainty in urban flood warnings.

Numerical Study on the Hydrologic Characteristic of Permeable Friction Course Pavement

The hydrologic characteristic of a permeable friction course (PFC) pavement is dependent on the rainfall intensity, pavement geometric design, and porous asphalt properties. Herein, the hydrologic characteristic of PFC pavements of various lengths and slopes was determined via numerical analysis. A series of analyses was conducted using length values of 10, 15, 20, and 30 m and slope values of 0.5%, 2%, 4%, 6%, and 8% for the equivalent water flow path. The PFC pavements were simulated for various values of rainfall intensity, which ranged from 10 to 120 mm/h, to determine the time taken for water to flow over the PFC pavement surface. The results show that the time for water overflow decreased when the pavement length or rainfall intensity increased, and it increased when the slope increased. Finally, a series of design charts was developed to determine the time taken for water to flow over the PFC pavement surface for given rainfall intensities. Since this study was conducted based on numerical analysis, further studies are recommended to verify experimentally the results presented.

Hydrologic Forecasts Verification and Comparison of Forecasting Methods

This paper presents the methods of estimating the mean square error of hydrological forecasts, allowing for assessment of their practical applicability. Depending upon the amount and composition of available hydrometeorological data, an appropriate method for forecast error estimation is chosen. A system of statistical tests for comparison of different forecasting methods for the same hydrologic characteristic with the same lead time is presented. These tests allow for choosing an optimal and most accurate forecasting method. Hydrological forecasting method efficiency estimation is based on comparing the forecast error with climatology or inertial (persistence) forecast error using presented tests.

Hydrologic Characteristics of Streamflow in the Southeast Atlantic and Gulf Coast Hydrologic Region during 1939–2016 and Conceptual Map of Potential Impacts

Streamflow is one the most important variables controlling and maintaining aquatic ecosystem integrity, diversity, and sustainability. This study identified and quantified changes in 34 hydrologic characteristics and parameters at 30 long term (1939–2016) discharge stations in the Southeast Atlantic and Gulf Coast Hydrologic Region (Region 3) using Indicators of Hydrologic Alteration (IHA) variables. The southeastern United States (SEUS) is a biodiversity hotspot, and the region has experienced a number of rapid land use/land cover changes with multiple primary drivers. Studies in the SEUS have been mostly localized on specific rivers, reservoir catchments and/or species, but the overall region has not been assessed for the long-term period of 1939–2016 for multiple hydrologic characteristic parameters. The objectives of the study were to provide an overview of multiple river basins and 31 hydrologic characteristic parameters of streamflow in Region 3 for a longer period and to develop a conceptual map of impacts of selected stressors and changes in hydrology and climate in the SEUS. A seven step procedure was used to accomplish these objectively: Step 1: Download data from the 30 USGS gauging stations. Steps 2 and 3: Select and analyze the 31 IHA parameters using boxplots, scatter plots, and PDFs. Steps 4 and 5: Synthesize the drivers of changes and alterations and the various change points in streamflow in the literature. Step 6: Synthesize the climate of the SEUS in terms of temperature and precipitation changes. Step 7: Develop a conceptual map of impacts of selected stressors on hydrology using Driver–Pressure–State-Impact–Response (DPSIR) framework and IHA parameters. The 31 IHA parameters were analyzed. The meta-analysis of literature in the SEUS revealed the precipitation changes observed ranged from −30% to +35% and temperature changes from −2 °C to 6 °C by 2099. The fiftieth percentile of the Global Climate Models (GCM) predict no precipitation change and an increase in the temperature of 2.5 °C in the region by 2099. Among the GCMs, the 5th and 95th percentile of precipitation changes range between −40% and 110% and temperature changes between −2 °C and 6 °C by 2099. Meta-analysis of land use/land cover show the region has experienced changes. A number of rapid land use/land cover changes in 1957, 1970, and 1998 are some of the change points documented in the literature for precipitation and streamflow in the region. A conceptual map was developed to represent the impacts of selected drivers and the changes in hydrology and climate in the study region for three land use/land cover categories in three different periods.

Analisis Perubahan Penggunaan Lahan Terhadap Karakteristik Hidrologi Di Das Bulok

Land use is one of the factors that have an effect on water system function of a watershed. The characteristic of hidrological condition at Bulok Watershed was degraded. This reaserch was carried out by analyzing data of rainfall, stream discharge, observation land use map, fluctuations of stream discharge and coefficient runoff at 2001, 2006, and 2011. The results of analysis were linked tabulated results with land use in descriptively. The results of this research showed by land use change, which were decreasing forests and mixed dryland farming area, increasing residential area and dryland farming area, which were decreasing forests and mixed dryland farming area, increasing residential area and dryland farming area was caused that the fluctuatoin of stream discharge in 2001 was to 12,45 and increased in 2006 was 51,27 and more increased in 2011 was 129,96. The coefficient runoff of Bulok Watershed has increased in 2001 was to 6% and increased in 2006 was 35% and more increased 2011 amounted to 41%. The increased fluctuation of stream discharge and coefficient runoff 2001-2011 showed that Bulok Watershed was degraded. Keywords : hydrologic characteristic, land use, watershed

Calculation of Design Flood for Small Watershed of Miaoyuanxi Stream

The flood in the mountainous area is characterized by remarkable outburst, low foreseeability, sudden rise and sudden fall and large destruction and is one of the natural disasters in rural area. In order to reduce the loss from mountain flood, this Thesis, taking the section of Siwu Village on the upstream of Miaoyuanxi Stream as the study object, conducts the calculation of the design flood for the small watershed of Miaoyuanxi Stream. The small watershed is short of the data of actually measured rainfall, especially runoff; therefore, based on the geographic information system (GIS), with irregular triangle net and spatial analysis function, we have realized the interpolation of the hydrologic characteristic value isoline of the research area; with frequency analysis, we have calculated the design rainfall of different time at different frequency and further calculated the design peak with the rational formula; in addition, with the hydraulic method, we have calculated the corresponding water depth of the three control sections of Siwu Village. The result shows that, the combination of small watershed design flood calculation and the GIS can make the hydrologic calculation more accurate and convenient. The research result may be the reference for the establishment of the flood prevention and avoidance guarantee system for the rural area.