Stormwater Infiltration Basins Research Articles

Variation in ground-dwelling arthropod communities across differently managed infiltration basins

Abstract As urbanisation continues to increase, terrestrial arthropod diversity declines. Urban green spaces represent unique opportunities to preserve arthropod diversity in urban environments. We quantify how ground-dwelling arthropod communities vary both seasonally and across three differently maintained stormwater infiltration basins in Ellisville, Missouri, United States of America. One basin was routinely mowed, a second was mowed only seasonally, and a third was intentionally planted to attract pollinators and was not mowed during this study. We expected higher plant diversity to correlate with higher arthropod diversity. Therefore, we expected the unmowed basin to have the highest levels of arthropod diversity and abundance and the mowed basin to have the lowest. Four collection periods spanned spring, early summer, late summer, and fall. During each collection period, five pitfall traps were placed throughout each basin for 48 hours. In total, 5686 specimens were collected and identified, representing 59 families. Arthropod communities did not vary across basins or collection dates, largely contrasting with existing literature. The results of this study do not indicate that different mowing regiments in infiltration basins will affect the ground-dwelling arthropod communities at a family level, although the effect on species-level diversity remains to be investigated.

In-depth characterization of sediment contamination in stormwater infiltration basins

Abstract Managing stormwater in infiltration-based systems enables the interception of runoff suspended solids. Accumulated particles form a layer of stormwater sediments, the contamination of which presents a critical challenge for maintenance operations but is still insufficiently understood. This study therefore aims to characterize the main contamination patterns of stormwater sediments. Sediments were sampled from 18 infiltration basins encompassing a diversity of catchments. Eighty-five substances, including metals and six families of organic micropollutants, were targeted, almost all of which were consistently quantified. A significant accumulation relative to baseline levels was ascertained in all sites. The geochemical signature of stormwater sediments was relatively close to that of road dust, but different from continental and marine sediments, revealing the contribution of urban-specific sources of contaminants. Common emission and transfer dynamics were inferred from strong correlations between metals; same observations were made for alkylphenols and the group formed by polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins, and furans. The predominant land use was generally insufficient to explain the inter-site variability of sediment contamination, which could still be understood from an in-depth study of each catchment and the identification of site-specific emission sources. These results constitute a milestone toward stormwater sediment reuse as a resource.

The influence of stormwater infiltration on downslope groundwater chemistry

Stormwater infiltration basins have been used extensively around the world to restore urban hydrology towards more natural flow and water quality regimes. There is, however, significant uncertainty in the fate of infiltrated water and accompanying contaminants that depends on multiple factors including media characteristics, interactions with downslope vegetation, legacy contaminants, and presence of underground infrastructure. Understanding the influence of such factors is thus central to the design and siting of infiltration basins. An extensive field program was established to collect monthly data on ground water quality, including nutrients and major ion concentrations, in a bore network downstream of a stormwater infiltration basin in Victoria, Australia. The groundwater samples were analysed for temperature, pH, EC, turbidity, major ions (Na+, Ca2+, K+, Mg2+, Cl−, SO42−, NO3−, CO32−, HCO3−), NOx and heavy metals. The collected data were used to understand the origin and fate of water and solutes in the subsurface and their interactions with the soil matrix. The results revealed that Ca–HCO3, Na–Cl water types predominate in the study area, grouped in 3 clusters; shallow fresh groundwater in the vicinity of the basin (near basin), deep saline groundwater further downstream of the basin (near-stream) and a mid-section where rock-water interaction (Na–HCO3 water) through cation exchange control the chemistry of groundwater. The results also suggest that as the water moves downstream of the basin, it experiences significant evapotranspiration and concentration due to the presence of deep-rooted vegetation. The results suggest that while infiltration basins can remove infiltrated contaminants, the infiltrated stormwater can mobilise legacy contaminants such as nitrate. Overall, the efficacy of infiltration basins in urban regions depends substantially on the downstream vegetation, urban underground infrastructure and the presence of legacy contaminants in the soils. These all need to be considered in the design of stormwater infiltration basins.

Time-Lapse Resistivity Monitoring of a Simulated Runoff Test in a Bioswale, Philadelphia

As part of the reconstruction of Interstate-95 in Philadelphia, a series of vegetated stormwater infiltration basins (bioswales) have been installed to manage highway runoff. To assess these bioswales, we used simulated runoff tests (SRTs), where the bioswale is flooded from a fire hydrant to simulate a major storm event. SRT monitoring relies on point measurements of inflow, outflow, and soil moisture to determine the volume of stormwater the bioswale can handle and the time to recovery. To provide better spatial coverage for site assessment, we tested the use of time-lapse electrical resistivity tomography (ERT) during a SRT. Using an onsite geophysical monitoring station, we performed ERT surveys every 4 h before, during, and after the SRT test. Inflow and outflow measurements taken during the SRT found that a majority of the water did not exit the bioswale via the outlet box. The time-lapse inversion results indicated that runoff uniformly spread throughout the basin before infiltrating into the heterogeneous urban soil below. The ERT demonstrated that the underlying native soil contributed to the overall performance of the bioswale, a contribution which was previously assumed to be minimal. Recovery to pretest soil moisture levels took roughly 2–3 days, according to both soil moisture sensors and time-lapse geophysical data. The SRT results were consistent with natural storm events recorded by our geophysical monitoring station, which have been monitored continuously for over a year. Use of ERT during SRTs characterize the pattern of infiltration and recovery rate of the soil beneath a stormwater control. Additionally, the heterogeneous infiltration observed during the SRT suggested that ERT surveys preconstruction may improve future planning of stormwater controls by guiding the location of infiltration measurements.

Modeling of stormwater infiltration basin enhanced with drywells technique

Modeling of stormwater infiltration basin enhanced with drywells technique

Aquifer recharge by stormwater infiltration basins: Hydrological and vadose zone characteristics control the impacts of basins on groundwater chemistry and microbiology

Stormwater infiltration systems (SIS) are designed to collect and infiltrate urban stormwater runoff into the ground for flood risk mitigation and artificial aquifer recharge. Many studies have demonstrated that infiltration practices can impact groundwater chemistry and microbiology. However, quantitative assessments of the hydrogeological factors responsible of these changes remain scarce. Thus, the present study aimed to quantitatively test whether changes of groundwater chemistry and microbiology induced by SIS were linked to two factors associated with vadose zone properties (vadose zone thickness, water transit time from surface to groundwater) and one factor associated with groundwater recharge rate (assessed by groundwater table elevation during rain events). To evaluate changes in chemistry (NO3−, PO43− and dissolved organic carbon concentrations), groundwater samples were collected in wells located in SIS-impacted and non-SIS-impacted zones during experimental periods of 10 days. During the same periods, clay beads were incubated in the same wells to measure changes of groundwater microbial biofilms (microbial biomass, dehydrogenase and hydrolytic activities) induced by SIS. Results showed that changes in PO43− supplied to groundwater during stormwater infiltration was negatively correlated with vadose zone thickness. A short water transit time from surface to groundwater increased dissolved organic carbon concentrations in the aquifer which, in turn, increased biofilm biomasses in groundwater. The groundwater recharge rate during rain events (assessed by groundwater table elevation) diluted NO3− concentrations in the aquifer but also influenced the changes of biofilm activities induced by SIS. Groundwater recharge rate during rain events probably increased the fluxes of water and dissolved organic carbon in groundwater, stimulating the activity of microbial biofilms. Overall, the present study is the first to quantify conjointly several factors and processes (water transfer, dilution, solute fluxes) that could explain the impact of stormwater infiltration on chemistry and/or microbiology in groundwater.

Stormwater drives seasonal geochemical processes beneath an infiltration basin.

Deicing salt is an important component of road safety during winter storms. Stormwater infiltration best management practices aim to prevent the salt from polluting streams and waterways, but this may shift pollutants to groundwater resources. In response to limited field studies investigating groundwater quality impacts caused by input of salt from stormwater infiltration best management practices, we monitored water levels and quality of groundwater at various depths in an unconfined aquifer around a stormwater infiltration basin using in situ sensors coupled with grab sampling. Our observations revealed differences in groundwater chemistry with depth in the aquifer and processes that were driven by the seasonal changes in the chemistry of stormwater (salt-impacted in winter and fresh in non-winter) recharging the aquifer. Water-matrix interactions in the vadose zone beneath the basin affected the transport of sodium (Na) into groundwater following non-winter recharge. Sodium movement through the aquifer was delayed relative to chloride (Cl), indicating a longer residence time of Na in the vadose zone. Radium (Ra) concentrations were correlated with Cl concentrations, suggesting salt-impacted recharge caused desorption of Ra into groundwater because of increased salinity. Stormwater-influenced groundwater followed a preferential flow path due to heterogeneity of the aquifer materials, and water chemistry varied with time and location along the flow path. These results highlight the importance of well screen length, placement and depth, and frequency of observations when designing a monitoring network.

Assessment of Stormwater Infiltration Basins Models Developed in Gaza Strip

Stormwater remains the sole source of aquifer recharge in the Gaza strip, which should be utilized properly through artificial infiltration. The study objective is to investigate and analyze the infiltration efficiency of three large exiting infiltration basins in the Gaza strip (Alamal, Asadaqa, and Waqf) using different infiltration techniques. The technique applied in Ala-mal basin is the natural surface spreading of stormwater while Asadaqa basin used the surface spreading combined with graveled boreholes. Waqf basin used non-graveled boreholes (empty shafts cased with UPVC pipes). The infiltration rate and efficiency were recorded and estimated for each basin during the 2021-2022 wet season and compared to a past 2017-2018 wet season at a water depth of 1.70 m. The study revealed that, the actual infiltration capacity of Waqf basin was estimated as 2,000 m3/day in the 2021-2022 wet season, twice that in the 2017-2018 wet season, with an infiltration efficiency of 57.47 %, that was attributed to the 18 drilled non-graveled boreholes, which enhanced the seepage of stormwater into the underlying soil. Asadaqa basin has the lowest infiltration efficiency of 3.90 % due to the continuous accumulation of thick and dense sediment layer on the basin floor, with nonchanged actual infiltration capacity (around 2,800 m3/day) between the two studied wet seasons. On the oth-er hand, Alamal basin infiltration efficiency was only 4.60 %, with actual infiltration capacity of 629 and 105.4 m3/day dur-ing the two wet seasons, respectively where some repair and upgrade works were performed at Alamal basin which enhanced the actual infiltration capacity but still far from the design infiltration capacity. For future studies, Waqf basin technique should be thoroughly studied and investigated as a novel artificial infiltration method, with deep study on the factors af-fecting the infiltration process.

Contaminant transport from stormwater management areas to a freshwater karst spring in Florida: Results of near-surface geophysical investigations and tracer experiments

Study regionSilver Springs is a karst spring in north-central Florida. As landuses in the springshed have urbanized in recent decades, concentrations of contaminants, including nitrate, have increased in spring water, causing environmental concerns. Study focusPathways of groundwater movement from stormwater management areas to Silver Springs were investigated using ground-based geophysical surveys (ground penetrating radar and frequency domain electromagnetics) accompanied by tracer tests in the Upper Floridan Aquifer (UFA) and surficial aquifer. Results indicated heterogeneous near-surface and deep karst conditions, where stormwater runoff may be transported quickly through groundwater to the spring. A wide range of groundwater velocities (10−6 to 10−3 ms−1) were observed in the surficial aquifer, where faster flow speeds were associated with subsurface anomalies and preferential flow. However, tracer injected into the UFA was observed in the spring hours later, suggesting possible maximum groundwater velocities on the order of 10−1 ms−1 in the karst aquifer. Series of tracer pulses in the spring highlight the complexity of flow pathways to Silver Springs. New hydrological insights for the regionThe rapid transport of tracer from stormwater basins to Silver Springs suggests that stormwater infiltration basins may be hotspots for potential aquifer and spring contamination in karst areas. Development of stormwater best management practices (BMPs) that integrate heterogeneous karst transport processes may enhance spring and groundwater quality in Silver Springs and other karst regions.

The Geochemical Signature of Sediments from Urban Stormwater Infiltration Basins

The Geochemical Signature of Sediments from Urban Stormwater Infiltration Basins

Impacts of stormwater infiltration on downslope soil moisture and tree water use

Infiltration of stormwater is a widely used strategy to mitigate the flooding and environmental risks that come from urban runoff and conventional urban drainage. An understanding of the fate of this infiltrated water is required for rigorous design. Principal design objectives are typically to restore more natural hydrology in order to protect receiving waters from pollution and hydrologic change. Without such understanding there is also a risk of unforeseen impacts on nearby infrastructure and urban vegetation. We sought to understand the pathways and fate of water from a stormwater infiltration basin. To trace water, we used a combination of water table monitoring and isotopic composition analysis in the infiltration basin, as well as in rainfall, soil water, the shallow groundwater, and in vegetation upslope and downslope of the basin. We also measured tree water use directly using sap flow sensors. The infiltration basin was shown to increase the availability of water downslope, allowing trees to maintain elevated levels of water use during dry periods with high energy demand. In contrast, water limitation upslope saw substantial seasonal reductions in tree water use. The soil water isotopic composition demonstrated significant differences from upslope to downslope, with downslope water being more reflective of rainfall, while the upslope water used by the trees was more depleted. The results paint a picture of stormwater infiltration being a significant source of lateral flow, while trees are a significant sink of lateral flow emanating from the basin. This finding suggests that stormwater infiltration could be used as a strategy to support the health and growth of urban trees. Urban trees have demonstrated benefits for human health and comfort, particularly in a warming climate. It also suggests that stormwater infiltration may not always recharge groundwater and provide baseflow in receiving waters, being instead taken up by vegetation. These findings should be considered in the siting of stormwater infiltration systems, to ensure that the objectives they were designed for are actually met.

Regenerating Stormwater Infrastructure into Biophilic Urban Assets. Case Studies of a Sump Garden and a Sump Park in Western Australia

The main purpose of this paper is to demonstrate how the old modernist engineering technologies, such as single purpose stormwater infiltration basins, can be transformed into quality environments that integrate ecological and social functions and promote multiple sets of outcomes, including biodiversity restoration, water management, and cultural and recreational purposes, among other urban roles. Using the principles and theories of biophilic urbanism, regenerative design, and qualitative inquiry, this article analyzes and discusses the actors, drivers, strategies, constraints, and values motivating the stakeholders to reinvent Perth’s stormwater infrastructure through two local case studies. The “WGV sump park” was developed through a public-private partnership, including professional consultants with community input, and the “Green Swing sump garden” was an owner-builder community-driven project involving volunteers, who maintain it. The results of this research suggest that both projects are successful at managing stormwater in a way that creates multiple community and biodiversity benefits. Communities could gain improved access to nature, social interaction, health, and well-being if local governments support these alternative approaches to regenerate underutilized stormwater infrastructure by promoting biophilic interventions. Mainstreaming this design approach identified some issues that may arise during the implementation of this biophilic urban approach, and the paper suggests ways to enhance the wider delivery of regenerative and biophilic design into urban planning, involving volunteer delivery and maintenance for small scale projects and fully professional assessments for large scale projects.

Inorganic Nitrogen Production and Removal along the Sediment Gradient of a Stormwater Infiltration Basin

Stormwater infiltration basins (SIBs) are vegetated depressions that collect stormwater and allow it to infiltrate to underlying groundwater. Their pollutant removal efficiency is affected by the properties of the soils in which they are constructed. We assessed the soil nitrogen (N) cycle processes that produce and remove inorganic N in two urban SIBs, with the goal of further understanding the mechanisms that control N removal efficiency. We measured net N mineralization, nitrification, and potential denitrification in wet and dry seasons along a sedimentation gradient in two SIBs in the subtropical Tampa, Florida urban area. Net N mineralization was higher in the wet season than in the dry season; however, nitrification was higher in the dry season, providing a pool of highly mobile nitrate that would be susceptible to leaching during periodic dry season storms or with the onset of the following wet season. Denitrification decreased along the sediment gradient from the runoff inlet zone (up to 5.2 μg N/g h) to the outermost zone (up to 3.5 μg N/g h), providing significant spatial variation in inorganic N removal for the SIBs. Sediment accumulating around the inflow areas likely provided a carbon source, as well as maintained stable anaerobic conditions, which would enhance N removal.

Environmental and economic implications of stormwater management alternatives in rural development

AbstractFloodplain restoration as a means of stormwater management (SWM) can benefit communities and the environment but is uncommonly chosen due to limited familiarity in rural and urban planning. This study uses life cycle assessment and life cycle costing (LCC) to compare four SWM alternatives for a typical rural setting undergoing development. We evaluate a case study in Lancaster County, PA in the Chesapeake Bay Watershed which, through community stakeholder planning, undertook a novel SWM plan by restoring its historic floodplain. We evaluate the life cycle impact assessment (LCIA) metrics, global warming (GW), eutrophication and acidification and cost for each alternative over a 100‐year period of analysis including construction, maintenance, and end‐of‐life decommissioning. Assuming a 5% discount rate, and that soils do not require off‐site hauling due to contamination, the cost and LCIA metrics for floodplain restoration are not significantly higher than the more conventional surface basin alternative. Although LCC is highly sensitive to the transport of soil off‐site, more than doubling the costs for the underground stormwater infiltration basin (USIB) and increasing eightfold the cost for the floodplain restoration, contaminated soil removal is rarely needed on rural land. For USIB, LCIA metrics are sensitive to the choice of recycling versus incinerating plastic components, with recycling resulting in lower GW; and for the permeable pavement alternative, additional maintenance to extend its lifetime shows favorable cost and reduced GW. We conclude that in rural settings where soil is not contaminated, floodplain restoration offers environmental and social benefits for SWM that outweigh its costs.

Use of passive sampling and high resolution mass spectrometry using a suspect screening approach to characterise emerging pollutants in contaminated groundwater and runoff

Groundwater systems are being increasingly used to provide potable and other water supplies. Due to human activities, a range of organic pollutants is often detected in groundwater. One source of groundwater contamination is via stormwater infiltration basins, however, there is little information on the types of compounds present in these collection systems and their influence on the underlying groundwater. We developed an analytical strategy based on the use of passive sampling combined with liquid chromatography/high resolution quadrupole-time-of-flight mass spectrometry for screening for the presence of pesticide and pharmaceutical compounds in groundwater and stormwater runoff. Empore™ disk-based passive samplers (SDB-RPS and SDB-XC sorbents) were exposed, using for the first time a new specially designed deployment rig, for 10 days during a rainfall event in five different stormwater infiltration systems around Lyon, France. Stormwater runoff and groundwater (via a well, upstream and downstream of each basin) was sampled. Exposed Empore™ disks were solvent extracted (acetone and methanol) and the extracts analysed using a specific suspect compound screening workflow. High resolution mass spectrometry coupled with a suspect screening approach was found to be a useful tool as it allows a more comprehensive analysis than with targeted screening whilst being less time consuming than non-targeted screening. Using this analytical approach, 101 suspect compounds were tentatively identified, with 40 of this set being subsequently confirmed. The chemicals detected included fungicides, herbicides, insecticides, indicators of human activity, antibiotics, antiepileptics, antihypertensive and non-steroidal anti-inflammatory drugs as well as their metabolites. Polar pesticides were mainly detected in groundwater and pharmaceuticals were more frequently found in runoff. In terms of detection frequency of the pollutants, groundwater impacted by infiltration was found not to be significantly more contaminated than non-impacted groundwater.

Anaerobic end-products and mitochondrial parameters as physiological biomarkers to assess the impact of urban pollutants on a key bioturbator.

The impact of long-term exposure (6months) to highly or slightly polluted sediments on the energy metabolism of an ecosystem engineer (the oligochaete Limnodrilus hoffmeisteri) was investigated in laboratory conditions. We evaluated some mitochondrial parameters (respiratory chain activity and ATP production rate) and the accumulation of anaerobic end-products (lactate, alanine, succinate, and propionate). The sediments were collected from stormwater infiltration basins and presented high levels of heavy metals and polycyclic aromatic hydrocarbons (PAHs). These compounds had been drained by the runoff water on impervious surfaces of urban areas during rainfall events. A decrease in the activity of the mitochondrial electron transport chain was observed in worms exposed to the most polluted sediment. Urban contaminants disrupted both aerobic metabolism and mitochondrial functioning, forcing organisms to shift from aerobic to anaerobic metabolism (which is characteristic of a situation of functional hypoxia). Although L. hoffmeisteri is very tolerant to urban pollutants, long-term exposure to high concentrations can cause disruption in mitochondrial activity and therefore energy production. Finally, this study demonstrated that anaerobic end-products could be used as biomarkers to evaluate the impact of a mixture of urban pollutants on invertebrates.

Water balance prediction in stormwater infiltration basins using 2-D modeling: An application to evaluate the clogging process

Sustainable urban drainage systems are built along roads and in urban areas to collect urban runoff and avoid flooding, and to filter water pollutants. Sediment collected by runoff is deposited in the stormwater basin and progressively reduces water infiltration efficiency, leading to the clogging of the basin. To help stormwater basin managers and stakeholders better understand and predict clogging rates in order to elaborate maintenance plans and schedules, water transport prediction models are necessary. However, because of the heterogeneous sediment hydrodynamic properties inside the stormwater basin, a two-dimensional (2-D) water flow model is required to predict water levels and possible overflow as accurately as possible. Saturated hydraulic conductivity (Ks) and sediment water retention curves were measured in the overall sediment layer of the stormwater basin, in addition to sediment layer thickness and organic matter content (11 sampling points). Sediment depth was used to predict organic matter (OM) content, and the OM was used to predict Ks. Water height in the basin was modeled with the HYDRUS-2D model by taking into account the sediment hydrodynamic properties distribution. The HYDRUS-2D model gave a satisfactory representation of the measured data. Scenarios of the hydraulic properties of stormwater basin sediment were tested over time, and hydraulic resistance, R, was calculated to assess the stormwater basin performance. Presently, after 20 years of functioning, the stormwater basin still ensures efficient water infiltration, but the first outflow (Hydraulic resistance, R > 24 h)) is expected to appear in the next 5 years, and clogging (R > 47 h) in the next 13 years. This 2-D water balance model makes it possible to integrate the hydrodynamic heterogeneity of a stormwater basin. It gives interesting perspectives to better predict 2-D/3-D contaminant transport.

Spatial and Temporal Stability of Major and Trace Element Leaching in Urban Stormwater Sediments

Urban sediment generated by stormwater management techniques are highly contaminated with various trace elements. The characterization of trace element speciation and mobility are critical information to improve environmental risk assessment. This study investigates the spatial and temporal variability of major and trace element release from a sedimentary layer in Django Reinhart stormwater infiltration basin (Chassieu, eastern suburbs of Lyon, France). Sampling was conducted for 3 zones and two dates. Chemical characterization was performed (X-Ray diffraction, ICP-AES). The samples were submitted to Acid Neutralization Capacity & Base Neutralization Capacity ANC-BNC tests, according to European standard 14429 (AFNOR, 2015). Solid matrices were mixed with acid or basic solutions and physicochemical parameters and major and trace element release (i.e. Al, Ca, Fe, P, S, Si, Cu, Zn and total carbon) were followed as a function of pH. The results show that the urban sediment has no significant spatial and temporal variability with regards to element release. This observation is all the more surprising that the samples were collected in three contrasting zones regarding stormwater supply and hydric conditions. Element release follows the same trends as a function of pH with a bell-shaped solubilization curve exhibiting with the highest solubility at extreme pH values. However, the samples showed slight differences concerning the release of major elements. Such differences are related to slight differences in total mineral contents (organic matter, carbonates…) and chemical composition of the sediments. The results show that despite the varying environmental conditions, the sediment chemical properties can be considered as very stable and uniform over space, depending mainly on the local geochemical context and watershed characteristics. This study highlights the strength and affluence of the information obtained by ANC-BNC tests on the release of major and traces metal elements by urban sediments and brings relevant information regarding the management of these sediments.

Ecological assessment of a transitioned stormwater infiltration basin

Infiltration basins are stormwater control measures (SCMs) widely employed for urban stormwater management. A transitioned infiltration basin is a failed infiltration basin that has gradually transformed into a wetland- or wetpond-like practice. The transitioned basin was found to effectively control the storm runoff flows and volumes, and improve the discharge water quality, thereby reducing the downstream hydrologic and pollutant loads on most occasions. Qualitative assessment of the site showed presence of wetland and non-wetland vegetation, small animals, and some potential for cultural benefit. The ecological evaluation demonstrated that runoff management and habitat provision in a sub-urban setting enhance the overall functionality of this new type of SCM ecosystem. A functionality assessment guide was developed for assessing infiltration basins considered to have failed. The Level-1 assessment includes visual criteria such as hydrophytic vegetation, hydric soils, hydrologic regime modification, and design check. The rapid assessment plans developed in this study can be applied to determine the ecological and stormwater management functions and benefits of failed/transitioning/transitioned basins, and may be adapted for other similar SCMs.

Impact of a Storm-Water Infiltration Basin on the Recharge Dynamics in a Highly Permeable Aquifer

Infiltration basins are increasingly used worldwide to both mitigate flood risk in urban areas and artificially recharge shallow aquifers. Understanding recharge dynamics controlling the quantity and quality of infiltrating water is required to correctly design and maintain these facilities. In this paper, we focus on quantitative aspects and analyze in detail the temporal evolution of infiltration rates in basins overlying highly permeable aquifers. In these settings, recharge is a complex process due to high recharge rate and volume, undetected soil hydraulic heterogeneity and topsoil clogging. A 16-ha infiltration basin in Northern Italy has been intensively characterized and monitored for over four years. Field and laboratory tests were performed to characterize soil hydraulic properties. An unsaturated-saturated numerical model was implemented to obtain additional quantitative information supporting experimental data. Results show a strong impact of the infiltration basin on natural recharge patterns. When properly maintained (no clogging of topsoil), estimated infiltration rates from the bottom of the basin are about fifty times higher than recharge under natural conditions in the same area. When the infiltration basin is not properly maintained, bioclogging progressively diminishes the infiltration capacity of the basin, which turns to have no impact on aquifer recharge. Recharge patterns are highly erratic and difficult to predict. We observed natural recharge rates of the order of 1 m/h and a poor correlation between recharge times and maximum intensity of rainfall events. Due to the complex behavior of the recharge, the numerical model (based on the classical Richards equation) is able to explain many but not all the observed recharge events. Macropores flow and Lisse effects on piezometric measurements may be responsible for the disagreement between model predictions and observations.