Regenerative Stormwater Conveyance Research Articles

A Better Understanding of Atmospheric Methane Sources Using 13CH3D and 12CH2D2 Clumped Isotopes

AbstractWe evaluate the use of clumped isotopes of methane (CH4) to fingerprint local atmospheric sources of methane. We focus on a regenerative stormwater conveyance (RSC) stream wetland site running through the University of Maryland campus, which emits methane due to its engineering. Air samples in the RSC were collected at different heights above the surface and at different times of the day including both early in the morning, after methane accumulated below the nocturnal boundary layer, and late in the afternoon when convection mixed air to the cloud layer. Measured Δ12CH2D2 values of air samples record mixing between locally produced methane with low D/H and ambient air. The Δ12CH2D2 of the near surface air collected at the RSC during the early morning ranges from ∼+23‰ to ∼+35‰ which is lower than the ∼+50‰ values of tropospheric air. Mixing between background air (with Δ12CH2D2 ∼+50‰) and methane captured from chamber and bubble samples, as well as produced in incubation (all with negative Δ12CH2D2), explains the observed values of Δ12CH2D2 and Δ13CH3D of near surface RSC air samples. The effect of mixing with biogenic sources on Δ13CH3D is much smaller. The findings demonstrate how methane isotopologues can be used as a tool not only to fingerprint local contributions to these greenhouse gas emissions but also to identify sources of near‐surface methane hot spots.

Changes in hydrology and pollutant loads from stream restoration in an urban headwater catchment

Stream restoration structures can alter the hydrology and biogeochemical processes of urban headwater streams in important ways. As a stream restoration design, regenerative stormwater conveyance (RSC) structures are built to reconnect floodplains to stream channels, raise the groundwater table, and increase streamwater retention times. Altered hydrology and flow dynamics within restored stream reaches can affect solute concentrations and loads in baseflow and stormflow runoff. We monitored interannual changes in precipitation, groundwater and stream runoff before and after the implementation of a stream restoration using an RSC design in order to evaluate changes in hydrology and to estimate changes in solute loads of an urban headwater catchment in the Rock Creek watershed of Washington DC. A Before After Control Impact (BACI) experimental design was used. Compared to the control catchment, average recharge of the groundwater system of the RSC riparian area increased by 0.76 m in the post-restoration period and contributed to a 6 % increase in baseflow as a percentage of total runoff (compared to a decrease of 6 % in the control catchment). Area yields from the pre- to the post-restoration monitoring period decreased in both the RSC and control catchments, but significantly larger decreases in total nitrogen (TN), total phosphorus (TP) and total suspended solids (TSS) occurred in the RSC catchment (i.e., −59 % vs −23 %, −54 % vs −28 %, and −76 % vs −40 %, respectively). Results of this study indicate that RSCs as stream restoration structures in degraded headwater catchments can result in important hydrological and biogeochemical changes that significantly reduce nutrient and sediment loads.

The effect of stormwater infiltration and surrounding built infrastructure on local groundwater dynamics: a case study for regenerative stormwater conveyances

ABSTRACT Infiltrated stormwater from a regenerative stormwater conveyance (RSC) investigated in Knoxville, TN, was found to substantially interact with the surrounding groundwater system. The degree of interaction resulted from seasonal fluxes in water table elevation, varying weather patterns and event sizes, and most significantly, the presence of two underground sewer lines. Mounding was observed below the RSC during small to medium storm events, which shifted to a sink for areas adjacent to the conveyance during larger events. The most prominent factor influencing trends in groundwater interactions appeared to be the presence of the sewer lines. This study shows the importance of understanding how the urban subsurface infrastructure network will influence groundwater interactions in order to avoid unintended consequences or short-circuiting of treatment mechanisms. These findings inform the scientific community of potential challenges when constructing infiltration-based stormwater controls in urban environments where a high density of buried infrastructure may be present.

Urban legacies: Aquatic stressors and low aquatic biodiversity persist despite implementation of regenerative stormwater conveyance systems

AbstractUrbanization is a global stressor of stream ecosystems. Watershed managers in urban regions often implement infiltration-based stormwater control measures (SCMs) to mitigate the effects of ...

Insights from using in-situ ultraviolet–visible spectroscopy to assess nitrogen treatment and subsurface dynamics in a regenerative stormwater conveyance (RSC) system

Regenerative stormwater conveyance (RSC) is a recently developed stormwater control measure that marries the concepts of bioretention and stream restoration. RSC mitigates stormwater runoff by converting surface flow to subsurface seepage using a series of pools and riffles built over a sand media bed. Subsurface seepage flows through media and exits the RSC beneath the outlet weir. Previous studies on RSC pollutant mitigation have focused on surface flow discharges from the RSC. To date, no known research has been conducted on the potential pollutant contributions of RSC seepage, despite the fact that this water also enters receiving waters. This research used Multi-Point Sampling coupled with in-situ ultraviolet–visual spectroscopy to measure nitrogen in seepage during simulated storm events (n = 9) at a field-scale RSC in Raleigh, North Carolina. Calibrations between light absorbance and concentrations were acceptable (Nash-Sutcliffe coefficient > 0.65) for nitrate and total ammoniacal nitrogen (TAN) and very good (Nash-Sutcliffe coefficient > 0.90) for total Kjehdahl nitrogen (TKN). Early storm simulations revealed some initial nutrient flushing from the substrate, which subsided by the third simulation. Overall, subsurface seepage nitrate, TAN, and TKN concentrations were lower by 29%, 57%, and 4% relative to storm inflow concentrations, respectively. Computed subsurface nitrogen concentrations demonstrated temporal variability, highlighting dynamic transport and biogeochemical transformations in saturated and unsaturated conditions. Nitrogen concentrations were lower in seepage than in surface flow; however, due to the high volume of runoff converted to seepage, nitrogen loads discharged in seepage can be larger than those of surface flow. Further research is needed to examine subsurface pollutant reductions under varying hydrologic and seasonal conditions.

Regenerative stormwater conveyance (RSC) for reducing nutrients in urban stormwater runoff depends upon carbon quantity and quality

Regenerative stormwater conveyance (RSC), a relatively new stormwater management approach, is extensively implemented throughout the mid-Atlantic for nutrient control, but little is known of its pollutant reduction capabilities and controlling factors. This study examined effects of organic carbon (C) quantity and quality on stream water quality and nutrient retention at two RSCs near Annapolis, Maryland, USA by comparing longitudinal changes in water quality at paired restored and unrestored stream reaches, and conducting lab experiments simulating RSC processes. Results showed that RSCs consistently had lower dissolved oxygen saturation (DO%) and pH relative to nearby unrestored streams, probably due to release of labile dissolved organic carbon (DOC). At one RSC, with high nitrate (NO3−) inputs, retention of N (16–37%) and release of DOC (18–54%) were observed with the highest retention of N during summer, and the rates of N retention and DOC release were larger than that of the adjacent unrestored tributary (N: 5–8%, DOC: <18%). At another RSC site with lower NO3− concentrations, N retention and DOC release were not apparent. Mesocosm experiments showed that NO3− retention varies with organic C quantity and quality depending on incubating temperature; retention of total N did not increase with organic C due to release of other N species (e.g., organic N). Lab mesocosms showed an increase in the release of soluble reactive phosphorus (SRP) with increasing organic C quantity and quality. However, field measurements did not show any evidence of SRP release at RSCs. The changes in SRP concentrations in streams seemed to be a function of iron levels and leaf litter inputs, but control factors for SRP warrant further investigation. This study suggests that RSC as a restoration approach may be effective for reducing N depending upon C quantity and quality as well as water temperature and N levels.

Water Quality and Hydrologic Performance of a Regenerative Stormwater Conveyance in the Piedmont of North Carolina

AbstractRegenerative stormwater conveyance (RSC) is an open-channel, sand-filtering system composed of a series of shallow aquatic pools, riffles and weirs, native vegetation, and underlying media ...

Performance of Regenerative Stormwater Conveyance on the Removal of Dissolved Pollutants: Field Scale Simulation Study

AbstractRegenerative stormwater conveyance (RSC) is a stormwater control measure (SCM) built in a channel that uses a series of riffles, grade control structures, and pools with an underlying sand ...

Hydrologic and water quality performance of regenerative stormwater conveyance installed to stabilize an eroded outfall

Conveying concentrated urban runoff to outfall locations frequently leads to stream bank erosion, channel incision, and the formation of headcuts. Installed in an incised eroded channel, regenerative stormwater conveyance (RSC) is a grade-control and treatment system that uses a series of pools and cascades with an underlying sand bed. As a recently developed practice, RSC performance evaluations are needed to improve the design and guide regulatory accreditation. An eroded channel with a 10% longitudinal slope was stabilized with a five-cell system and monitored for a 14-month period. A small capture volume (6-mm design event) and groundwater intrusion resulted in minimal hydrologic benefit. Hydrologic mitigation was attained only for storms less than 12.7mm. The RSC converted a substantial 50% of inflow to media flow at the second cell; however, the media flow entirely reemerged as surface flow in the saturated downstream pools. Small but statistically significant reductions in event mean concentrations occurred: 17% total suspended sediment (TSS), 17% total phosphorus (TP), and 3% total nitrogen (TN). Water quality improvements occurred primarily between the upstream and second cell, indicating limited processing by the wetter downstream pools. Comparisons between inter-event outflow grab samples and storm event outflow concentrations show nitrogen export during inter-event periods (47% increase in TN concentration). Due to elevated inter-event concentrations, overall mass loading of nitrogen increased. Hydrologic and water quality benefits were garnered only in the first three cells where groundwater intrusion was minimal. Future implementations of RSC are encouraged to account for seasonal high water table elevations that interact with the RSC media and adequately size pool and sand layer capture volumes.

Hydrologic Performance of Regenerative Stormwater Conveyance in the North Carolina Coastal Plain

AbstractRegenerative stormwater conveyance (RSC) is an open channel, sand-filtering system composed of a series of shallow aquatic pools, riffle weirs, native vegetation, and underlying media beds....

Regenerative Stormwater Conveyance Provides Needed Treatment for Runoff Volume, Peak Discharge, and Quality Control for New Development or Retrofitting Underserved Watersheds

Regenerative Stormwater Conveyance Provides Needed Treatment for Runoff Volume, Peak Discharge, and Quality Control for New Development or Retrofitting Underserved Watersheds