Impervious Area Ratio Research Articles

Exploring the influence of urban agglomeration on extreme precipitation: Evidence from the middle reaches of the Yangtze River, China

Study regionThe urban agglomeration in the middle reaches of the Yangtze River (MRUA) consisting of 31 cities is a pillar of the Yangtze River Economic Belt and the largest urban agglomeration in China, densely populated, and rapidly urbanizing. Study focusExtreme precipitation events are affected by rapidly urbanized regions with uneven levels of urbanization. Hence, it is important to explore the spatiotemporal evolution of extreme precipitation in urban agglomerations and the influence of the spatially uneven development of urban areas under rapid large-scale urbanization. New hydrological insights for the regionExtreme precipitation indices (Pmax1d, R20, and PF95) exhibited significant positive trends during 1979–2018 in the MRUA, increasing by 0.43 mm/year, 0.11 day/year, and 2.46 mm/year, respectively. Regression models based on raster urbanization data were constructed, and the impervious area ratio (IA) and landscape shape index (SI) were shown to be the dominant urbanization factors affecting regional extreme precipitation, with a particularly positive spatial correlation with PF95 and Pmax1d at all stages of urbanization. Moreover, the urban-rural comparison results revealed that the difference in SI of each city was positively correlated with the urban heat island intensity. In the three provincial capitals, Pmax1d and R50 were greater in urban centres than in rural areas. This study contributes to a comprehensive understanding in the variability of extreme precipitation events under the influence of large-scale urbanization.

Study on the Coupling Relationship between Thermal Comfort and Urban Center Spatial Morphology in Summer

The high-density development of urban centers has worsened outdoor thermal comfort in many cities. In this study, ENVI-met was used to simulate thermal comfort, and the universal thermal climate index (UTCI) and eight urban morphological indicators were calculated at 348 sampling points in the urban center. The correlation results are shown as follows: (1) Thermal comfort is significantly and positively correlated with impervious surface, green area ratio, and sky openness, showing a strong negative correlation with building density, floor area ratio, and shadow hours. (2) The UTCI value decreases by 0.998 °C for every 1 h increase in shadow hours, increases by 0.746 °C for every 10% increase in sky view factor, decreases by 0.462 °C when the building density increases by 10%, and decreases by 0.596 °C for every 10% increase in the impervious area ratio. (3) The sampling points with better thermal comfort have similar spatial characteristics such as higher building density, higher volume ratio, smaller green area ratio, longer shadow hours, and smaller sky openness. (4) In the planning and design of urban centers, increasing shade can improve the shadow hours in the environment. Specifically, large open sites should be avoided.

Distribution characteristics of impervious area according to urban watershed development status and calculation of average impervious area ratio by land use

Distribution characteristics of impervious area according to urban watershed development status and calculation of average impervious area ratio by land use

An Integrated Approach for Urban Pluvial Flood Risk Assessment at Catchment Level

With the rapid development of urbanization and global climate change, urban pluvial floods have occurred more frequently in urban areas. Despite of the increasing urban pluvial flood risk, there is still a lack of comprehensive understanding of the physical and social influencing factors on the process. To fill this knowledge gap, this paper proposes a novel approach to calculate the comprehensive urban pluvial flooding risk index (PFRI) and investigates the interplay impacts from different components at catchment level. To be more specific, PFRI is determined by two components, Exposure Index (EI) and Social Vulnerability Index (SoVI). EI is evaluated based on two indicators, the depression-based Topographic Control Index (TCI) and impervious area ratio. SoVI is measured based on a set of demographic and socio-economic indicators. Our results demonstrated the spatial heterogeneity of urban pluvial flood exposure and social vulnerability, as well as the composite flooding risk across the study area. Our catchment-based urban pluvial flooding risk assessment method can provide a comprehensive understanding of urban flooding and promote the formulation of effective flood mitigation strategies from the catchment perspective.

Development and Assessment of Watershed Management Indicators Using the Budyko Framework Parameter

This study aims to introduce the Budyko curve’s parameter (w) as a watershed quality indicator and establish criteria. Basin-specific (w) was calculated in 183 watersheds based on land use in 2013. Weather data and runoff data were used, and runoff data were calculated using Hydrological Simulation Program-Fortran (HSPF). An estimation model was developed to estimate the w of the unmeasured watershed, and the R2 of the developed model was 0.917, showing that the modeled value was reliable. A cluster analysis between basin-specific w and impervious area ratio in 2013 was performed to classify watershed quality. w was classified into four grades according to the dendrogram and impervious cover model. Watershed quality in 1975 and 2013 was evaluated using the developed indicators and criteria. The quality grades of 30 watersheds deteriorated, and the deteriorated watershed increased built-up and decreased forest and grass. To evaluate the indicators’ applicability, the low impact development (LID) method was applied to HSPF to confirm the indicator and criteria changes. It showed that the watershed to which LID was applied has improved indicator and reduced grade. The indicator developed in this study is expected to be useful for watershed quality assessment and analysis of improvement effects according to watershed management.

Development of Flood Vulnerability Assessment Method considering Urban Characteristics: Daegu Metropolitan City

This study intends to develop a flood vulnerability assessment method and flood damage reduction measures in urban areas for Daegu Metropolitan City. The proxy variables for the flood vulnerability assessment were calculated using the previously investigated proxy variables for urban areas. The Flood Vulnerability Index (FVI) of the urban area was proposed using the Regional Significance Index (RSI), which indicates the importance of each region, and the Damage Possibility Index (DPI) for flood damage data. The RSI selected four proxy variables: population density, vulnerable population ratio, property density, and area ratio of major facilities. The DPI also selected four proxy variables: area ratio of low land, the impervious area ratio, status of domestic disaster risk district, and flood occurrence record. Eight proxy variables were selected and the FVI of urban areas calculated using multiplicative utility functions. As a result of the calculation, the FVI of Daegu Metropolitan City was found to be high in the central urban areas and by the streams. The results of this study are expected to be used for flood vulnerability assessments in urban areas and establishing flood damage reduction measures.

Spatial heterogeneity of controlling factors’ impact on urban pluvial flooding in Cincinnati, US

Urban pluvial flooding has become a common threat for urban areas. Intensified rainfall, increasing imperviousness, and insufficient drainage capacity contribute to the increase of pluvial flood risk. The strategy of risk mitigation relies on the understanding of these controlling factors of urban pluvial flooding. However, spatial heterogeneity of the impacts of controlling factors has received limited attention. This study analyzes how topography, rainfall, impervious surfaces affect urban pluvial flooding and how the effects vary in space. A case study in the city of Cincinnati, US based on four storm events in recent years is conducted. The impact of topography is measured by a depression-based empirical parameter, Topographic Control Index (TCI), which is generated based on depression ponding volume, contributing area, and upstream slope. Rainfall depth estimated from kriging interpolation method is used to measure how the rainfall affect the urban pluvial flooding. The impervious area ratio of the contributing area of each depression as well as that of observed flooded locations are calculated to analyze the influence of impervious area. The results showed that TCI value and rainfall intensity are spatially correlated with the presence of flooded locations, and flooded locations can be classified into two types: rainfall control or topography control. The imperviousness of land surface does not show a significant correlation with pluvial flood due to the relatively small spatial variation of impervious area in a well-developed city. The framework in this study could identify the spatial distribution of dominant controlling factors for pluvial flooding, which is critical for the effective planning of mitigation measures.

A Machine Learning Ensemble Approach Based on Random Forest and Radial Basis Function Neural Network for Risk Evaluation of Regional Flood Disaster: A Case Study of the Yangtze River Delta, China.

The Yangtze River Delta (YRD) is one of the most developed regions in China. This is also a flood-prone area where flood disasters are frequently experienced; the situations between the people–land nexus and the people–water nexus are very complicated. Therefore, the accurate assessment of flood risk is of great significance to regional development. The paper took the YRD urban agglomeration as the research case. The driving force, pressure, state, impact and response (DPSIR) conceptual framework was established to analyze the indexes of flood disasters. The random forest (RF) algorithm was used to screen important indexes of floods risk, and a risk assessment model based on the radial basis function (RBF) neural network was constructed to evaluate the flood risk level in this region from 2009 to 2018. The risk map showed the I-V level of flood risk in the YRD urban agglomeration from 2016 to 2018 by using the geographic information system (GIS). Further analysis indicated that the indexes such as flood season rainfall, urban impervious area ratio, gross domestic product (GDP) per square kilometer of land, water area ratio, population density and emergency rescue capacity of public administration departments have important influence on flood risk. The flood risk has been increasing in the YRD urban agglomeration during the past ten years under the urbanization background, and economic development status showed a significant positive correlation with flood risks. In addition, there were serious differences in the rising rate of flood risks and the status quo among provinces. There are still a few cities that have stabilized at a better flood-risk level through urban flood control measures from 2016 to 2018. These results were basically in line with the actual situation, which validated the effectiveness of the model. Finally, countermeasures and suggestions for reducing the urban flood risk in the YRD region were proposed, in order to provide decision support for flood control, disaster reduction and emergency management in the YRD region.

Hydrologic and Water Quality Evaluation of a Permeable Pavement and Biofiltration Device in Series

Two stormwater control measures (SCMs) installed in series were monitored for their individual impact on the hydrology and water quality of stormwater runoff from a 0.08-hectare watershed in Fayetteville, North Carolina, for 22 months. Runoff was first treated by permeable interlocking concrete pavement (PICP), the underdrain of which discharged into a proprietary box filter (Filterra® biofiltration) which combined high-flow-engineered media with modest biological treatment from a planted tree. Due to a deteriorating contributing drainage area and high ratio of impervious area to permeable pavement area (2.6:1), clogging of the permeable pavement surface caused an estimated 38% of stormwater to bypass as surface runoff. Fifty-six percent of runoff volume infiltrated underlying soils, and the remaining 6% exited the Filterra® as treated effluent; the hydrologic benefit of the Filterra® was minimal, as expected. Primary treatment through the PICP significantly reduced event mean concentrations (EMCs) of total suspended solids (TSS), total phosphorus (TP), total nitrogen (TN), and total Kjeldahl nitrogen (TKN) but contributed to a significant increase in nitrate/nitrite (NO2,3–N) concentrations. Secondary treatment by the Filterra® further reduced TSS and TP concentrations and supplemented nitrogen removal such that treatment provided by the overall system was as follows: TSS (removal efficiency (RE): 96%), TP (RE: 75%), TN (RE: 42%), and TKN (RE: 51%). EMCs remained unchanged for NO2,3–N. Despite EMC reductions, additional load reduction due to the Filterra® was modest (less than 2%). This was because (1) a majority of pollutant load was removed via PICP exfiltration losses, and (2) nearly all of the export load was from untreated surface runoff, which bypassed the Filterra®, and therefore the manufactured device never had the opportunity to treat it. Cumulative load reductions (based only upon events with samples collected at each sampling location) were 69%, 60%, and 41% for TSS, TP, and TN, respectively. When surface runoff was excluded, load reductions increased to over 96%; lower run-on ratios (which would reduce clogging rate) and/or increased maintenance frequency might have improved pollutant load removal.

설계기준 변경에 따른 유출계수 추정 - 공원을 중심으로 -

합리식은 유역 면적, 강우강도와 토지이용 또는 표면형태에 따라 결정되는 일정한 범위의 유출계수로 이루어져있다. 2011년에 개정된 하수도시설기준에서는 5~10년 재현기간의 설계홍수량을 증가하기 위해 재현기간을 10~30년으로 조정하였다. Ponce, ASCE 등은 재현기간(강우강도)이 클수록 큰 유출계수를 적용할 것을 제시하고 있으나, 재현기간의 상향조정에 따른 유출계수의 증가에 대하여서는 현재 조정되지 않은 상태이다. 본 연구에서는 토지이용 및 표면형태에 많은 차이를 보이는 공원을 대상으로 불투수면적비 변화와 설계확률년수 조정에 따른 유출계수를 추정하고자 한다. 첫째, 20개 도시에서 무작위로 선정된 1,004개 공원을 대상으로 표면형태별 면적비를 구하여 유출계수를 추정하였다. 둘째, 재현기간 조정에 대한 영향은 재현기간 10년에 대한 30년의 유출계수비를 69개 기상관측소 지점에 대하여 지속기간별로 구하였다. 이에 따라, 표면형태의 차이와 재현기간 조정을 고려한 재현기간 10~30년 에 대한, 공원의 유출계수는 0.43~0.54의 범위를 가지는 것으로 나타났으며, 지역적 편차와 지속기간별 편차는 크지 않는 것으로 나타났다. The rational method is formed area, rainfall intensity and runoff coefficient that is representation of land use or surface type. A runoff coefficient is a range for a each surface conditions. Drainage Sewer Design Guideline revised at 2011 proposes return periods 10~30 year instead of 5~10 year for increasing design flood. Ponce and ASCE refer higher values of runoff coefficient require for higher values of rainfall intensity and return period, therefore runoff coefficient had to be corrected but not. In case of park, land use and surface type are different from Korea and U.S, so impervious area ratio is different. The runoff coefficient for park is estimated considering with impervious area ratio and return period. 1,004's parks in 20 cities are randomly selected for impervious area ratio and runoff coefficient is estimated. And a proportion of 30 year return period runoff coefficient to 10 year return period with rainfall duration is calculated for 69 weather stations. The estimated runoff coefficient is 0.43~0.54 for return period 10~30 year and the difference of region and rainfall duration is not significant.

Assessing impervious area ratios of grid-based land-use classifications on the example of an urban watershed

ABSTRACTWhen applying a distributed hydrological model in urban watersheds, grid-based land-use classification data with 10 m resolution are typically used in Japan. For urban hydrological models, the estimation of the impervious area ratio (IAR) of each land-use classification is a crucial factor for accurate runoff analysis. In order to assess the IAR accurately, we created a set of vector-based “urban landscape GIS delineation” data for a typical urban watershed in Tokyo. By superimposing the vector-based delineation map on the grid-based map, the IAR of each grid-based land-use classification was estimated, after calculating the IARs of all grid cells in the entire urban watershed. As a result, we were able to calculate the frequency distribution of IAR for each land-use classification, as well as the spatial distribution of IARs for the urban watershed. It is evident from the results that the reference values of IAR for the land-use classifications were estimated very roughly and inherited errors of between about 7% and 70%, which corresponds to more than 100 mm increase of direct runoff for the 1500 mm annual average precipitation.Editor D. Koutsoyiannis; Guest editor E. Volpi

도시지역 오프라인 빗물저류조 운영방법 개발

최근 도시지역 불투수면적비가 올라가고 도시침수를 발생시키는 강우의 횟수는 점점 증가하고 있다. 이로 인하여 침수 발생 횟수가 증가하고 있으며 이에 대한 해결책은 다양하다. 침수 문제를 해결하기 위한 방법으로는 구조적 대책과 비구조적 대책이 있다. 본 연구에서는 비구조적 대책 중에서 내배수시설의 운영에 초점을 맞추었다. 내배수시설 중 도시유역에 설치되는 오프라인 빗물저류조를 대상으로 하여 연구를 실시하였다. 우수관거의 상황을 고려한 저류 및 방류를 실시하여 빗물저류조 내에서의 추가적인 저류공간을 확보하는 운영을 제안하였다. 확률강우를 이용하여 최초월류발생지점을 고려한 모니터링 지점을 선택하고 모니터링 지점의 수위에 따라 빗물저류조의 운영이 결정되었다. 새로운 운영방법의 효과를 검증하기 위하여 기존에 침수가 발생했던 2010년, 2011년 강우를 강우-유출 모델에 적용하였다. 새로운 운영을 적용한 결과 기존 빗물저류조 운영에 비해 2010년의 경우 최대 28.52%, 2011년의 경우 최대 16.81%의 침수저감효과를 보였다. Recently, the ratio of impervious area, the number of extreme rainfall and runoff in urban areas are dramatically increasing. Because of this reasons, the number of flood disasters are also increasing and there are several measures such as structural measures and nonstructural measures. In this research, operation of drainage facilities among non-structural measures is focused. Operation in urban offline detention reservoirs among drainage facilities was studied. Operation obtaining additional capacity in detention reservoir by storage and discharge considering the status of sewer network was suggested. First flooded node in sewer network was selected as a monitoring point using probability rainfall data and operation of offline detention reservoir was determined according to the level of monitoring point. For verifying effects of new operation, rainfall data in 2010 and 2011 were applied to. In the case of 2010, maximum flood reducing effect of new operation was 28.52% and in the case of 2011, maximum flood reducing effect of new operation was 16.81%.

Assessing Impervious Area Ratios of Grid-based Land Use Classifications on the Example of an Urban Watershed

When applying a distributed hydrological model in urban watersheds, grid-based land use classification data with 10 m resolution are typically used in Japan. Land use classifications into 17 categories are made without taking into account their impermeable properties. Thus, for such a grid-based urban hydrological model, the estimation of the Impervious Area Ratio (IAR) of each land use classification is a crucial factor for accurate runoff analysis in urban watersheds. However, so far IAR of each classification is estimated very roughly and applied in the corresponding hydrologic models almost empirically. Thus in order to assess the IAR accurately, we created a set of vector-based “urban landscape GIS delineation” data for a typical urban watershed in Tokyo using detailed land use recognition, which exactly delineated the pervious and impervious features into 20 land use types in the watershed. These vector data are used to improve the impervious area depiction of grid-based land use classifications. By superimposing the vector-based delineation map on the grid-based map, the IAR of each grid-based land use classification was estimated with very little uncertainty, after calculating the IARs of all grid cells in the entire urban watershed. As a result, we were able to calculate the frequency distribution of IAR for each land use classification as well as the spatial distribution of IARs for the urban watershed.

Prioritizing subwatersheds for non-point source pollution management in Saemangeum watershed using AHP technique

The objective of this study was to investigate non-point sources (NPS) pollution and prioritize management areas affected by NPS pollution in the Saemangeum Watershed. AHP (Analytical Hierarchy Process) technique was selected to prioritize sub-watersheds for effectively managing NPS pollution in this study areas. Generation properties of NPS pollution, discharge properties of NPS pollution, and runoff properties of NPS pollution were selected and set for AHP. Weighted descriptors including indicators like numbers of livestock, land- and livestock-system loads, rainfall, and impervious area ratio were generalized from 0 to 1 and multiply each index based on screened 17 survey data. The results were visualized as maps which enable resource managers to identify sub-watersheds for effective improving water quality. The sub-watersheds located in Gongdeok-Myeon, Yongji-Myeon, Hwangsan-Myeon of Gimje-Si were selected for managing NPS pollution control areas. This result presented that these sub-watershed are more affected by the pollution from livestock-system than from land-system. The finding from this study can be used to screen sub-watersheds that need further assessment by managers and decision-makers within the study area.

Sediment and total phosphorous contributors in Rock River watershed

Total phosphorous (TP) and total suspended sediment (TSS) pollution is a problem in the US Midwest and is of particular concern in the Great Lakes region where many water bodies are already eutrophic. Increases in monoculture corn planting to feed ethanol based biofuel production could exacerbate these already stressed water bodies. In this study we expand on the previous studies relating landscape variables such as land cover, soil type and slope with changes in pollutant concentrations and loading in the Great Lakes region.The Rock River watershed in Wisconsin, USA was chosen due to its diverse land use, numerous lakes and reservoirs susceptible to TSS and TP pollution, and the availability of long-term streamflow, TSS and TP data. Eight independent subwatersheds in the Rock River watershed were identified using United States Geological Survey (USGS) monitoring sites that monitor flow, TSS and TP. For each subwatershed, we calculated land use, soil type, and terrain slope metrics or variables. TSS and TP from the different subwatersheds were compared using Analysis of Variance (ANOVA), and associations and relationships between landscape metrics and water quality (TSS and TP) were evaluated using the partial least square (PLS) regression. Results show that urban land use and agricultural land growing corn rotated with non-leguminous crops are associated with TSS and TP in streams. This indicates that increasing the amount of corn rotated with non-leguminous crops within a subwatershed could increase degradation of water quality. Results showed that increase in corn–soybean rotation acreage within the watershed is associated with reduction in stream's TSS and TP. Results also show that forest and water bodies were associated with reduction in TSS and TP. Based on our results we recommend adoption of the Low Impact Development (LID) approach in urban dominated subwatersheds. This approach attempts to replicate the pre-development hydrological regime by reducing the ratio of impervious area to natural cover wherever possible, as well as recycling or treating stormwater runoff using filter strips, ponds and wetlands. In agriculturally dominated subwatersheds, we recommend increasing corn–soybean rotation, keeping corn on areas with gentle slope and soils with lower erodibility.

Application of remote sensing information about land use – land cover in flood forecasting with the Xin'anjiang model

Grid-based digital elevation data with a spatial resolution of 30 s of latitude or longitude, covering the Hanjiang River basin, were matched spatially with a 1 km × 1 km grid of land use – land cover data generated from remotely sensed data. The ratio of impervious area to subcatchment area (denoted IMP), a parameter in the Xin'anjiang model, can then be extracted directly from the land use – land cover data. Soil free water storage capacity (SM), a sensitive parameter in the Xin'anjiang model, can be obtained for the subcatchment by the relation between SM and the ratio of forest land area to subcatchment area. Thus, in the proposed semidistributed hydrological model, the spatial variability of land surface characteristics is taken into consideration. As a result, the physical meanings of model parameters are so clear that they can be extended from gauged catchments to ungauged catchments according to the land surface characteristics over the catchments. The accuracy of flood forecasting is improved as well. A case study of 24 flood events within the Baohe River, the upper tributary of the Hanjiang River, has shown that constructing the relationship between model parameters and land surface characteristics is an effective way to reduce errors in flood forecasting. In concrete terms, if the result computed by the semidistributed algorithm is compared with the result obtained by the lumped subcatchment algorithm, the Nash–Sutcliffe coefficients of 15 flood events increase, and the relative errors of 22 flood peaks decrease markedly. Also, the sensitivity of SM to flood peak discharge is greater than its sensitivity to the Nash–Sutcliffe coefficient. The semidistributed hydrological model is of practical value to flood forecasting and to the quantitative description of land use – land cover change related to the water cycle. We are convinced that this research is also helpful in the operation of a water supply system for the middle route of the large project involving water transfer from southern to northern China.