Peak Flow Reduction Research Articles

River-floodplain interaction and flood wave routing along rivers flowing through Pantanal wetlands

The Pantanal is the largest tropical wetland in the world and has extraordinary biodiversity, being considered of great ecologic value. Besides the intimate dependence of Pantanal ecosystems, functioning, and integrity on water dynamics, the flood pulse and inundation also regulate traditional riverside communities’ way of life, recreational fishing tourism, jaguar tourism, cattle raising, navigation, and agriculture. This study advances in characterizing flood wave dampening, flood wave travel time, and lateral exchanges of water of rivers flowing along the Pantanal, investigating the relationship between these characteristics and the upstream flood. A dynamically coupled 1D-2D hydrological modeling approach, already calibrated on earlier work is used, to simulate the main channel flood wave routing, water inundating and moving across the floodplain, and channel-floodplain bidirectional interaction. Four upstream flooding scenarios were imposed, simulating contributing floods from uplands (Planalto), that enter and flow along each of the major rivers of the Pantanal region. The results indicate that flood wave travel time is directly related to the size of the upstream flood, but the presence of secondary peak flows before or after the major flood peak did not have a marked influence. Patterns of reduction or increase in peak flow along the river reaches were also identified, which were independent of the size and shape of the upstream flooding condition. For the uppermost reaches of all rivers, the loss of water from the main channel to the floodplain heavily attenuates the flood hydrograph. This flood dampening showed to be stronger for larger floods, as there is more proportion of channel flow spilling over to the floodplains. However, in absolute terms, these results showed that upstream floods of different sizes or with different shape characteristics (multiple or single peak flows) present quite similar flood hydrographs as one moves downstream along the Pantanal region, becoming typically unimodal smoothed flood hydrographs.

A multi-objective decision-making framework for implementing green-grey infrastructures to enhance urban drainage system resilience

Green-grey infrastructures implementation for addressing urban flood damages and urban drainage system’ (UDS) resilience (respectively) needs comprehensive evaluation under various planning and design influencing factors. In this paper, a multi-objective decision-making framework is developed for the optimization of green-grey infrastructures to understand the trade-off between benefits and retrofit costs under various design configurations, rainfall intensities, and system performance indicators. In the developed framework, the grey infrastructure locations are optimally determined by using Analytic Hierarchy Process (AHP) method with three defined indicators (e.g., flood volume and flood duration of flooding nodes, sensitivity of flooding nodes) and maximum percentage of each type of green infrastructure (GI) in each sub-catchment based on land-use analysis as a preliminary step of the multi-objective optimization process, followed by decision-making procedure. The application results reveal that optimal designs of grey infrastructure are more cost-effective and may have a significant influence on the reduction of flood damages and outlet peak flow compared to GI from their individual evaluations, while GI improves UDS’ functionality performance indicators (e.g., resilience, reliability, and sustainability) better than grey infrastructure. However, a combined implementation of both infrastructures boosts their advantages because of the synchronization effect compared to individual scenarios, providing the most cost-effective optimal UDS designs. Moreover, the cost-effectiveness of coupled green-grey infrastructures designs could be enhanced from lower to higher design storms because of higher rate of utilization of stormwater infiltration and storage capacities of both infrastructures. The framework presented in this study can be conveniently generalized to other case-studies for optimal implementation of green-grey infrastructures as long as including their local economic parameters, climatic patterns, urban development plans and green-grey infrastructures design guidelines.

Two-scale optimal management of urban runoff by linking LIDs and landscape configuration

Landscape composition and configuration of urban patches impact greatly on hydrological process, of which low impact development practices (LIDs) have been incorporated worldwide to management stormwater runoff quantity- and quality-related issues. Although optimization design for LIDs has been studied extensively to improve stormwater management at catchment scale, a further study of LIDs-based landscape configuration at site scale has not been fully explored. In this study, a two-scale optimization framework was constructed to integrate spatial layout and landscape configuration of LIDs using SWMM, NSGA-II and GIS techniques. The spatial optimization at catchment scale showed that area of sink landscape almost doubled as the distance to outlets decreased. A further site-scale optimization by a new landscape metric, in terms of CRSS (configuration ratio between patches of runoff sources and sink), was conduct to achieve LIDs-based landscape configuration optimization. Runoff flow and pollution were significantly correlated with CRSS in power function, quantifying CRSS thresholds of 0.57–0.69 as the most adaptive strategies for stormwater management. Notably, the CRSS thresholds were higher for ammonia nitrogen (NH3-N) and suspended solid (SS) pollution, especially targeting source patches of roofs. The optimization in this study could improve the reduction of runoff peak flow of heavy rain, peak concentration of chemical oxygen demand and SS, and initial scouring of NH3-N.

Determination of Grass Swale Hydrological Performance with Rainfall-Watershed-Swale Experimental Setup

High urbanization adversely affects the hydrological behavior of watersheds. Therefore, different stormwater management strategies have been put forward to mitigate these negative effects. Grass swales are one of the environmentally friendly practices that are widely used today as an alternative to traditional infrastructure systems to reduce the peak flow rates, increase infiltration, and the time of concentration. The determination of the effective parameters on the hydrological characteristics of grass swales plays an important role in identification of proper design criteria. To this end, hydrological experiments were conducted by designing a grass swale module and integrating it into a large-scale rainfall-watershed-swale (RWS) experimental setup. The potential effective parameters (rainfall, soil, grass type, drainage area, and grass height) on the hydrological performance of the grass swales were tested with six different swale configurations by the controlled laboratory experiments. Experimental results show that swales decrease the peak flow significantly. In addition, hydrological performance of swales decreases with the increase in rainfall intensity or rainfall duration. Moreover, the soil and grass type have a significant effect on the peak flow reduction and drainage performance of the swales.

Hydrologic Performance of Permeable Pavers and a Dome Concrete Forming System: A Comparative Study

The hydrologic performance of permeable interlocking concrete pavers (PICP) and a dome concrete forming system (DCFS) was quantified and evaluated at a retrofitted residential laneway in Toronto, Ontario. The quantification and evaluation were performed by comparing their monitored performance over 14 months with an adjacent concrete pavement. Their monitored performance was then used to assess their ability to mimic predevelopment hydrologic behavior, estimated through modeling. The PICP and DCFS achieved (1) an average runoff volume reduction of 33% and 85%; (2) an average runoff coefficient of 0.48 and 0.12; and (3) an average peak flow reduction of 43% and 89%, respectively. The outflow duration from the DCFS was extended 4.1 times greater than the inflow duration, indicating its potential to attenuate flashy events. The peak flows produced by the DCFS were delayed by nearly 2.5 h from those occurring on the PICP. Correlation analyses indicated a more significant influence of rainfall depth and intensity on the performance of PICP than that of the DCFS. Compared with predevelopment levels, PICP did not match runoff volumes for smaller events (<10 mm) but produced less runoff for larger events (>30 mm). However, the PICP did not match predevelopment peak flows in 100% of occurrences. The DCFS reduced runoff volumes and peak flows to magnitudes lower than all predevelopment levels. Surface infiltration testing and subsurface hydraulic conductivity estimations indicated that infiltration capability in both systems could be reduced over time. The study demonstrated that the DCFS might need to be prioritized over permeable pavements, especially when installed over low-permeability soils.

Glacier contribution to lowland streamflow: A multi-year, daily geochemical hydrograph separation study in subarctic Alaska

Glacier melt water is a critical fresh water contribution of stream discharge for many regions and in high latitudes glacier extent is decreasing with climate warming. However, characteristics of glacierized contributions to subarctic watershed-scale geochemistry and runoff have attracted limited attention. Tracer studies of glacier dominated watersheds are also commonly limited to a few days. We conducted a six-year geochemical hydrograph separation study of melt season daily streamflow in a glacierized watershed in Interior Alaska to estimate glacier, rain, snow, and baseflow contributions. Bulk streamflow water samples were collected daily from the lowlands of Jarvis Creek (634 km2, 3.3% glacier cover) throughout the flow season (late April through September) during 2011–2016. Synoptic sampling of source waters included rain, snow, headwater late-winter streamflow and late-summer glacier terminus discharge. All 1227 source water and bulk streamflow samples were analyzed for stable water isotopes (δ18O and δD) and dissolved ion concentrations (SO42−:Cl− ratio). Bulk streamflow water samples exhibited large seasonal and inter-annual geochemical variation. Considerable inter-annual differences in stable water isotopes within each source water (δ18O values of −15.8 to −20.9‰ for rain, for example) emphasize the importance of informing the mixing model with source waters sampled during the same season as bulk streamflow collection. We estimated glacier discharge to be the largest seasonal contributor to total warm season lowland streamflow (average 35%, ranging from 20% in year 2016 to 44% in 2012) with daily variability from 2 (June 2, 2011) to 80% (September 10, 2013). If the glacier contribution were to cease completely, total warm season bulk stream discharge would be reduced by between 22 and 48% during an above or below average total seasonal rainfall, respectively, with up to an 80% reduction in peak flows. Results from this study suggest that high variability in source contribution of glacierized watersheds, extending across intra- and interannual timescales, challenge any generalization of hydrologic function derived from short-term studies.

Comparison on the stormwater runoff effects of roof greening in different urban functional areas

Global climate change and the expansion of impervious surface in urban areas have increased the risk of urban flood. As a measure with low impact development (LID), roof greening can effectively reduce stormwater runoff, serving as the first barrier to prevent rainwater from entering the urban drainage system. We used the CITYgreen model to simulate and analyze the impacts of roof greening on hydrological parameters (e.g., surface runoff) in the new and old residential areas and the commercial areas in Nanjing City, and further investigated the variations in stormwater runoff effects (SRE) among these functional areas. We compared the SRE between different green roof types, and between green roofs and ground-level green spaces. The results showed that the proportion of permeable surface would increase by 28.9%, 12.5% and 49.2% respectively in the old residential area, new residential area and commercial area if all building roofs were greened. In a rainfall event with a return period of two years and a duration of 24 hours (precipitation=72 mm), the implementation of roof greening in all buildings in the three sampling areas could reduce surface runoff by 0-19.8% and reduce peak flow by 0-26.5%. The reductions in runoff by green roofs could be translated to a rainwater storage capacity of 223-2299 m3. The commercial area had the highest SRE by installing green roofs, followed by the old residential area, while the new residential area had the lowest SRE. The rainwater storage volume by per unit area of extensive green roof was about 78.6%-91.7% that of the intensive green roof. The storage capacity by per unit area of green roof was 31%-43% of that in the ground-level greenery. The results would provide scientific references for the site selection, sustainable design and incentive development of roof greening from the perspective of stormwater management.

Flood Mitigation Performance of Permeable Pavements in an Urbanised Catchment in Melbourne, Australia (Elizabeth Street Catchment): Case Study

Permeable pavement (PP) systems have been shown to provide onsite stormwater management as well as contaminant removal benefits. Therefore, significant research has taken place in recent years to analyse the performance of these structures in terms of the volume of stormwater harvested and the water quality improvements at small scales. However, there is limited understanding of their performance for reducing stormwater runoff volume to prevent natural disasters, such as catchment-scale flooding. With larger flooding events projected to occur more frequently as a result of urbanisation and climate change, PP systems have the potential to mitigate loss by reducing peak flows and runoff volumes. Therefore, this research investigates the performance of PP at the catchment scale under a range of design rainfall and land-use scenarios. Results indicate that the integration of permeable pavements in urban settings is effective in mitigating surface flooding in an urbanised catchment in Melbourne, Australia by reducing the peak flows by 7–16%. However, in practice, flood reduction ability can markedly decrease with time due to the clogging of pavements. Our results provide preliminary data to show that the integration of permeable pavements into the existing urban landscape can reduce the risk of flooding by providing areas for water to infiltrate if maintained properly. These results are envisioned to assist councils and stormwater managers with the option evaluation of the water-sensitive urban design systems and selecting the appropriate stormwater management measures.

Assessing hydrological performance for optimized integrated grey-green infrastructure in response to climate change based on shared socio-economic pathways

Integrated grey-green infrastructure (IGGI) is considered as a promising facility for mitigating urban flooding during extreme rainfall events. However, most IGGI strategies rely heavily on historical precipitation data, while ignoring the long-term effects of dynamic and non-stationary climate change. This study explored a novel approach to assess the hydrological performance under Shared Socio-economic Pathways (SSPs) based on long-term rainfall time series, facilitating the exploration of the optimal solution to urban runoff alleviation in response to climate change. A case study of Guangzhou, China, was applied for model validation. The results indicated that through non-stationarity analysis and stage division, the future time series of the three SSPs were identified with an abrupt point and divided into two stages. By assessing the hydrological performance of the optimal solutions at various historical and future stages, both fully centralized IGGI and decentralized IGGI are found vulnerable to long-term climate change. Based on a certain extent of trade-off between centralization and decentralization, an appropriate degree of decentralization was observed to significantly enhance the hydrological performance of the whole IGGI system, particularly for reducing peak flow following extreme rainfall events. The authors believe that the findings could provide a novel perspective on hydrological performance assessment for IGGI in response to non-stationary and multi-scenario climate change in urban catchments with high built-up density.

The Possibilities of Capturing Rainwater and Reducing the Impact of Floods: A Proposal for the City of Beira, Mozambique

Modern societies face various challenges, including climate change, rapid urbanization, and sometimes inadequate urban planning policies. In recent years, extreme weather events have received increasing attention for their impacts on cities, humans, and ecosystems worldwide, particularly on coastal towns in Mozambique, such as cyclones, floods, water pollution, and water scarcity, demonstrating their vulnerability to climate change. Cities must adapt to cope with the pressure on their water resources, and it is essential to ensure that communities have access to safe, reliable, and affordable water. A viable way to promote this resilience and simultaneously reduce costs in domestic budgets is to use rainwater to meet daily needs where water quality parameters are not required for consumption. According to the results of this study, it is possible to significantly reduce potable water use from the municipal water supply network by harvesting rainwater, up to 40% when the use does not require potable water at all, proactively protecting this vital resource. In addition to these direct benefits, the large-scale deployment of rainwater harvesting (RWH) systems in densely urbanized areas can also provide indirect benefits, such as reducing peak flow volumes in stormwater drainage systems and potentially reducing the frequency of urban floods. These benefits result from the reduction in the volume and duration of water sent to the drainage network, which can help to improve the overall resilience of communities in the face of climate change and other challenges.

Multi-objective decision-making based on theories of cooperative game and social choice to incentivize implementation of low-impact development practices

Urbanization growth leads to shifting hydrological factors which in turn represent a challenge for urban stormwater management. In this situation, policy strategies can be employed by governments to incentivize stakeholders to use green infrastructure for effective runoff management. This study presents a novel framework evaluating the application of Low-Impact Development (LID) practices for runoff quality and quantity management from a socio-economic point of view. The proposed framework investigates the potential of cooperative game theory to find a fair allocation based on the concept of justice. In this regard, first, the Non-dominated Sorting Genetic Algorithm (NSGA-II) was coupled with the Storm Water Management Model (SWMM) to find optimal runoff management scenarios considering minimization of runoff volume, peak flow, Total Suspended Solid (TSS) load, and costs of LIDs implementation. In the next step, in order to conflict resolution, stakeholders' preferences and interactions were incorporated into the cooperative game theory to determine management scenarios' worth of coalition. In the third step, benefits are allocated among stakeholders by defining three different sharing rules. Then, to select the most capable runoff management scenario, social choice methods of Condorcet choice, Borda scoring, and median voting rule support cooperative game decisions. The proposed methodology is explored in District 10 of Tehran municipality in Iran. According to the findings, solutions with stricter plans for runoff management correspond to more worth of coalition. In addition, the higher worth of coalition, the higher the reduction of peak flow, TSS load, and the total runoff volume. The results also reveal that the Borda scoring procedure tends to select scenarios with less reduction in TSS load, runoff volume, and peak flow in comparison with the others, and as expected, the minimum value for the worth of coalition. Additionally, the cooperative game targets a management scenario with the highest worth of coalition and the maximum value for the reduction in runoff volume, peak flow, and TSS removal. Our framework warrants runoff volume, TSS load, and peak flow can be reduced by 32.8, 31.9, and 32.7 percent, respectively. This framework, in addition to incentivize the stakeholders for implementing runoff management strategies, can effectively consider their conflict of interests in the decision-making process.

Dynamic disequilibrium: Recent widespread increases in vegetation cover on subarctic floodplains of Interior Alaska

AbstractBoreal forest and tundra ecosystems are undergoing rapid climatic and environmental changes with consequences for ecosystem structure, function, and services. Although riparian zones occupy a small footprint within subarctic landscapes, they have disproportionately high value as foci of hydrological processes, biogeochemical cycling, ecological disturbance, biodiversity, and wildlife activity. Recent observations of increased winter discharge, reduced peak flows, and increased connectivity between catchments, streams, and groundwater in subarctic riparian zones have prompted predictions of altered riverine disturbance regimes, increased channelization, and a decline in the extent of active floodplains. However, few observational data exist concerning the spatiotemporal dynamics of subarctic floodplain vegetation, which can serve as a bioindicator to corroborate such predictions. We analyzed the distribution and extent of riparian ecotypes across a network of streams in 12 Interior Alaska watersheds using high‐resolution image pairs from circa 1981–2010. All stream reaches encompassed pronounced elevational gradients and included elevational forest–tundra ecotones. We classified riparian ecotypes using an image‐based point‐intercept sampling approach, calculated the probability of ecotype transitions, and evaluated relationships between ecotype transitions and environmental covariates. Our results reveal widespread increases in the stature, density, and extent of riparian vegetation spanning gradients of elevation, floodplain morphology, and climate. Ecotype transitions occurred at &gt;20% of sample points, and there was a strong imbalance toward forward successional transitions (16.5%) versus backward transitions (4.0%). That is, we observed a strong tendency toward increasing cover, stature, and density of vegetation communities across our extensive sampling domain across our approximately 30‐year sample period. This relatively rapid riparian “greening” signal tended to be most pronounced in our glaciated watersheds. Although the streams we studied displayed high local variability in ecotype transitions, our results support hypotheses of increasing channelization and reduced extent of unvegetated surfaces on subarctic floodplains. They also likely reflect a trend toward more rapid and extensive plant recruitment and growth due to processes associated with conspicuous warming in northern ecosystems, consistent with greening documented in other subarctic landscape segments along gradients of elevation and latitude.

Simulation of the peak flow reduction of small reservoirs. A case study of the Brown Bridge Pond, Michigan, USA

Simulation of the peak flow reduction of small reservoirs. A case study of the Brown Bridge Pond, Michigan, USA

Low-Sloped Rooftop Storm-Water Detention Assembly to Mitigate Urban Flooding

Low-sloped roofs such as commercial and high-rise buildings in a dense urban area provide vast “unused” surfaces that can be used to manage storm-water and mitigate urban flooding. Storm-water Detention Assembly (SDA) known as “blue roof” exerts advanced drainage technologies and operational strategies to store-and-release storm-water during and after heavy rainfall events. SDA can reduce peak flow and decrease storm-water run-off volume. However, the SDA application is limited due to the lack of science-based regulatory requirements. This paper introduces SDA, summarizes the benefits and challenges of this system, reviews the existing code specifications on roofing drain systems, and documents the criteria to design and construct SDA. With this systematic approach, the missing links are identified that shall form code change request for possible inclusion in the National Building Code of Canada (NBCC) and National Plumping Code of Canada (NPC). In addition, a road map is stated to calculate and benchmark the drain requirements on low-sloped roofs for a given design climatic load.

Evaluating the Peak Flow and Runoff Coefficient Reductions of Bioretention, Infiltration Trench, and Permeable Pavement LID Using Stormwater Management Model

Evaluating the Peak Flow and Runoff Coefficient Reductions of Bioretention, Infiltration Trench, and Permeable Pavement LID Using Stormwater Management Model

Verification of PCSWMM's LID processes and their scalability over time and space

IntroductionThis paper explores the scalability of PCSWMM's Low Impact Development (LID) modeling tools within the urban stormwater computer model.MethodsThe scalability is assessed for a variety of spatial and temporal scales and for event (50-year return storm) and continuous inputs (daily rainfall for an 11 month period), and with a focus on bioretention cells. The model is calibrated for a moderate to large scale, semi-urban watershed on Vancouver Island, British Columbia, Canada. Sensitivity analysis and specialized metrics are used to verify internal model processes at a variety of scales.ResultsWith regard to spatial scaling, changes in flow path length and slope derived from Digital Elevation Models were the most impactful spatial information when modeling flood event and the model's surface layer was the dominant contributor to peak flowrate and volume mitigation by the bioretention cell. However, when modeling the continuous rainfall inputs, storage layer related parameters dominated model outputs. Aside from the soil layer's depth, soil layer parameters such as hydraulic conductivity, showed negligible influence on response to time series rainfall. Parameters that are kept static by the model such as vegetation cover, hydraulic conductivity and storage void ratio (but are naturally dynamic), were tested for their impact on response if allowed to change seasonally or with excessive loading. Runoff coefficients were greatly impacted by storage layer parameter dynamics with very little impact from vegetation. For event simulations, the berm height in the surface layer was the dominant player in reducing peak flow as well as total volume. An analysis to help illustrate sensitivity across spatial scales is proposed.DiscussionThe Spatial Dynamic Sensitivity Analysis shows that parameter sensitivity changes dynamically as LID implementation percentage changes. In particular, the clogging factor, which is a parameter associated with the storage layer, was highly influential for time series rainfall analysis. The LID model concepts in PCSWM seem appropriate for events because the surface layer dominates the response for very large storms. For smaller storms, continuous time series, and larger spatial scales, the model could be revised to better represent soil layer dynamics and vegetation cover, which were both currently inconsequential to the model's output.

Green infrastructure drainage of a commercial plaza without directly connected impervious areas: a case study.

A paired-catchment study of two adjacent commercial areas in northern Sweden, one with Green Infrastructure (GI) storm drainage and the other with a conventional storm sewer system, served to evaluate the hydrological performance of both drainage systems and demonstrate advantages of GI. The GI catchment avoided directly connected impervious areas by diverting runoff from a parking lot to a cascade of three infiltration features, a fractured rock strip draining onto a sloping infiltration area, followed by a collector swale. Both catchments were monitored over 4 years by measuring rainfall, runoff and, in the vicinity of the swale, soil water content and groundwater levels. For frequent storms, the median GI efficiencies in reducing runoff volumes and peak flows, and extending peak flow lags, were 96, 99 and 60%, respectively, compared to conventional drainage. The storm rainfall depth, initial soil water content, increases in intra-event soil water storage and groundwater levels had statistically significant effects on either runoff volume or peak flow reductions. No effects were found for storm rainfall intensity and duration, antecedent dry days, and initial groundwater levels. The study demonstrated that GI drainage can be successfully applied even in the challenging environment of a subarctic climate.

Impact of residential rainwater harvesting on stormwater runoff

Population increase, climate change and soil impermeability are factors causing floods in large urban centres. Such places also always have water shortage problems. This research aims to evaluate the influence of rainwater harvesting in residential buildings on stormwater in a basin located in southern Brazil (Rio Cachoeira Basin). Urbanised and non-urbanised areas, soil types, curve numbers and time of concentration of each sub-basin were taken into account. Through the HEC-HMS programme, it was possible to calculate hydrographs for the base scenario (when there is no rainwater harvesting). Then, rainwater tanks for the residential buildings were sized using the computer programme Netuno. In the second scenario, there is rainwater harvesting in all residential buildings. Thus, the hydrographs for the second scenario were also calculated. The peak flow reduction potentials for the sub-basins ranged from 2.7% to 14.3%. The highest percentage (14.3%) did not occur in the sub-basin with the most extensive roof area; such highest peak flow reduction occurred in Bom Retiro sub-basin. In Bom Retiro sub-basin, there are more houses than multi-storey residential buildings. Even when considering the full potential of rainwater harvesting for roof areas of all existing buildings in the Rio Cachoeira Basin, the average potential reduction in peak flow was 7.2%. The conclusion is that rainwater tanks in residential buildings have little influence on stormwater runoff, and the stormwater runoff will be less affected when the area of the hydrographic basin is larger. Thus, the reduction in peak flows is insignificant when considering the flooding in the region.

Evaluation of comprehensive treatment effect of geotechnical and ecological engineering for debris flow: case of Wenchuan County, Sichuan Province

As a crucial link in debris flow disaster control, control engineering can be divided into geotechnical engineering and ecological engineering. Geotechnical engineering is less affected by climate and can play an immediate role in the treatment of debris flow in a short time. Ecological engineering has obvious regulating effect on surface runoff and erosion. Furthermore, there are few discussions on comprehensive treatment effect between geotechnical engineering and ecological engineering for debris flow. Therefore, taking the debris flow gullies with control engineering implemented in Wenchuan area of Sichuan Province as the research object, this paper puts forward an evaluation method of treatment effect comprehensively considering the geotechnical engineering and ecological engineering. It is mainly based on the impact of engineering on the formation conditions of debris flow and the damage of projects. The comprehensive treatment effect of geotechnical and ecological engineering for debris flow is analyzed. The corresponding evaluation indexes are extracted, including 5 first-class evaluation indexes such as landform factor and water source factor, as well as 11 s-class evaluation indexes such as the peak flow reduction rate, the sediment retention ratio and the LAI ratio. The Fuzzy-AHP method is used to establish the evaluation model of treatment effect. The evaluation results are graded. It is considered that the treatment effect of other debris flow gullies is medium or above except that two gullies are poor. The evaluation results are consistent with the actual investigation, which provides a reference for the control of debris flow in this area.

Effects of Design and Climate on Bioretention Effectiveness for Watershed-Scale Hydrologic Benefits

Bioretention areas are a common form of green stormwater infrastructure (GSI). There is significant research on the performance of individual bioretention cells, but the watershed-scale benefits of GSI are still unclear. Furthermore, differences in bioretention design and rainfall patterns make it difficult to compare results between studies. We used the Storm Water Management Model (SWMM) to assess the effects of bioretention size, soil infiltration rate, storm size, and climate on the watershed-scale performance of GSI. We first divided the contiguous US into 10 rainfall regions based on similarities in precipitation amount, intensity, and other storm characteristics. We then modeled the effects of bioretention areas in a single watershed under these different rainfall regimes. Bioretention areas did provide watershed-scale benefits, although performance declined as (1) bioretention areas became smaller, (2) soil infiltration rates decreased, and (3) precipitation depth increased. High-intensity rainfall was the primary cause of outflow from bioretention areas, although back-to-back storm events also caused outflow in some climates. There were some clear discrepancies between subbasin-scale and watershed-scale GSI performance. Generally, runoff volume reduction was greater when measured at the subbasin scale. Peak flow reduction, however, was greater at the watershed-scale, likely because bioretention areas changed the shape of subbasin runoff hydrographs, leading to watershed-scale peak flow reduction that was greater than the sum of the parts. We provide recommendations for design, management, and future research to help advance effective application of GSI for achieving watershed-scale hydrologic benefits.