Blind Inlets Research Articles

Soil Phosphorus in Farmed Potholes: Assessing Concentrations and Testing Export Mitigation with Steel Media

Highlights Phosphorus concentrations were higher near the bottom of farmed potholes compared to soils outside of the potholes. Benchtop flow-through experiments demonstrated that steel shavings effectively adsorbed dissolved reactive phosphorus. A blind inlet amended with steel shavings reduced phosphorus export from a surface-drained pothole. Abstract. The Prairie Pothole Region, which extends from north-central Iowa northward into Canada and westward to Montana, is typified by closed depressions that formed over 10,000 years ago during the most recent glacial retreat. Today, many of these potholes contain artificial drainage to lower the water table, allowing for agricultural production of the land. Even when drained, farmed potholes can become inundated with phosphorus (P) enriched surface waters after large rain events. The goal of this study was to characterize the spatial distribution of soil P in farmed potholes and evaluate a steel media-modified blind inlet as a tool to reduce P export from farmed potholes. Results from the soil sampling indicated that Bray-1 soil test P concentrations are nine times higher near the bottom of the pothole compared to locations outside of the farmed pothole. Steel shavings were evaluated for P sorption in a laboratory flow-through cell evaluation where they removed between 60 and 70% (discrete P), even when cumulative P loading was over 6000 mg kg-1. In a field investigation, a modified blind inlet containing a mixture of steel shavings and pea gravel replaced a Hickenbottom surface intake. The modified blind inlet retained an average of 83% of the influent dissolved reactive P and 62% of the influent total P based on five paired samples. The results from this study demonstrate that farmed potholes contain a significant amount of legacy soil P and that blind inlets containing steel shavings can replace surface intakes and reduce P export from farmed potholes. This research could inform future design and implementation of these P removal structures. Keywords: Drainage, Farmed wetland, French drain, Iron filings, Iron shavings, Iron tailings, Prairie pothole, Surface intake, Tile.

Utilization of Steel Slag in Blind Inlets for Dissolved Phosphorus Removal

Blind inlets are implemented to promote obstruction-free surface drainage of field depressions as an alternative to tile risers for the removal of sediment and particulate phosphorus (P) through an aggregate bed. However, conventional limestone used in blind inlets does not remove dissolved P, which is a stronger eutrophication agent than particulate P. Steel slag has been suggested as an alternative to limestone in blind inlets for removing dissolved P. The objectives of this study were to construct a blind inlet with steel slag and evaluate its ability to remove dissolved P, nitrogen (N), and herbicides. A blind inlet was constructed with steel slag in late 2015; data from only 2018 are reported due to inflow sampling issues. The blind inlet removed at least 45% of the dissolved P load and was still effective after three years. The dissolved P removal efficiency was greater with higher inflow P concentrations. More than 70% of glyphosate and its metabolite, and dicamba were removed. Total N was removed in the form of organic N and ammonium, although N cycling processes within the blind inlet appeared to produce nitrate. Higher dissolved atrazine and organic carbon loads were measured in outflow than inflow, likely due to the deposition of sediment-bound particulate forms not measured in inflow, which then solubilized with time. At a cost similar to local aggregate, steel slag in blind inlets represents a simple update for improving dissolved P removal.

Hydrologic assessment of blind inlet performance in a drained closed depression

Surface inlets installed in agricultural closed depressions can transport sediment- and nutrient-laden runoff directly to receiving streams or water bodies. Replacing tile risers with blind inlets has the potential to decrease these sediment and nutrient loads, but adoption of blind inlets has been met with hesitation from producers who fear that changes to the surface inlet may result in additional water ponding, crop damage, or crop loss. The objectives of this study were to assess hydrologic performance of blind inlets over time, and to determine whether blind inlets influenced the hydrology of a closed depression compared to a tile riser. Hydrograph characteristics including flow duration, time to peak flow, peak flow rate, and cumulative flow were evaluated for 549 storm events over a 12-year period (2006 to 2017) for a pair of closed depressions in northeastern Indiana. Surface water could be drained in both depressional areas with either a tile riser or blind inlet. Results showed that blind inlet infiltration rates declined approximately linearly over time (1.4 cm h⁻¹ y⁻¹). While changes in infiltration were largely controlled by annual tillage practices at the study sites, findings suggest that blind inlets have an effective service life of 8 to 10 years under the study conditions. Surface water management practices significantly influenced depression hydrology; however, the practices functioned differently between fields. Blind inlets did not influence the frequency of discharge, but they may increase or decrease the duration of flow and cumulative flow compared to a tile riser depending on the extent of subsurface tile drainage within the closed depression. Findings from this study underscore the inherent connections between surface and subsurface hydrologic processes in drained closed depressions and how these connections may influence both water quantity and water quality.

The past, present, and future of blind inlets as a surface water best management practice

Drainage of tile-riser inlets allow direct discharge of surface water into tile drainage systems, effectively bypassing soil filtration processes and negatively affecting water quality. Blind inlets have gained recent popularity in allowing for both depression drainage and removal of suspended particulate matter by filtration through a sand/gravel layer. This paper summarizes blind inlet development and all published studies, provides new data from dissection of the longest-operating blind inlet that was recently de-commissioned, and discusses new ideas for the future of blind inlets, given certain shortcomings. Previous studies, as well as current soil analysis of the 12-yr old blind inlet confirmed the ability of blind inlets to reduce sediment and particulate phosphorus (P), with an overall removal efficiency of at least 40% for each. In addition to sediment and particulate P, soil sampling revealed the ability of the blind inlet to capture several pesticides: glyphosate, atrazine, S-metolachlor, and metabolites. Traditional blind inlet sand media are unable to remove appreciable amounts of dissolved P compared to alternative media such as steel slag. Enhanced removal of dissolved constituents could be easily achieved through use of P sorption materials and organic materials such as biochar, as well as combination with tile-drain filters.

Using the Conservation Practice Effectiveness (CoPE) Database to assess adoption tradeoffs

The newly published Conservation Practice Effectiveness (CoPE) Database compiles information on the effectiveness of a suite of conservation practices developed to treat contaminants in surface runoff and tile drainage water from agricultural landscapes. Traditional conservation practices such as no-tillage and conservation crop rotation are included in the CoPE Database, as well as novel practices such as drainage water management, blind inlets, and denitrification bioreactors. This will be particularly useful to conservation planners seeking new approaches to water quality problems associated with dissolved constituents, such as nitrate (NO₃) or soluble phosphorus (SP), and for researchers seeking to understand the circumstances in which such practices are most effective. Another novel feature of the database is the presentation of information on how individual conservation practices impact multiple water quality concerns. This information will be critical to enabling conservationists and policy makers to avoid (or at least be aware of) undesirable tradeoffs, whereby great efforts are made to improve water quality related to one resource concern (e.g., sediment) but exacerbate problems related to other concerns (e.g., NO₃ or SP). Finally, we note that the CoPE Database can serve as a source of the soft data needed to calibrate simulation models assessing the potential water quality tradeoffs of conservation practices, including those that are still being developed.

CoBAGNPS: A Toolbox to Estimate Sediment Removal Efficiency of WASCoBs–Pipe Risers and Blind Inlets

Water and Sediment Control Basin (WASCoB) is an important BMP constructed along concentrated flow-paths (gullies etc.) to control the movement of water and sediment within a watershed. A WASCoB constitutes of a berm, surface inlets, and a drainage pipe to route water into a ditch. Direct runoff ponded behind the berm is routed through surface inlets into an underground drainage pipe. Therefore, surface inlets are an exceedingly important constituent of a WASCoB. Further pipe risers and blind inlets are the two most common type of surface inlets used. Therefore, maximum sediment removal efficiency of WASCoBs at a watershed-scale can be attained by the appropriate selection of a surface inlet, since the efficiency of a WASCoB is greatly impacted by the quantity of runoff and sediment leaving the surface inlet. In this study a toolbox was developed viz., CoBAGNPS to compute the sediment removal efficiency of pipe risers and blind inlets. A watershed-scale model (AGNPS) was integrated within the toolbox. Output files of the AGNPS model are fed as input files into the toolbox where a sediment routing module is programmed separately for pipe risers and blind inlets to obtain the sediment removal efficiency for each type of surface inlet. Further, the sediment routing module programmed for blind inlets integrates the AGNPS model with the HYDRUS 1-D model. The toolbox developed was applied to the Gully Creek watershed in Ontario, and the sediment load routed through pipe risers and blind inlets were compared.

Investigation of Atrazine Sorption to Biochar With Titration Calorimetry and Flow-Through Analysis: Implications for Design of Pollution-Control Structures.

Atrazine is one of the most common broad-leaf herbicides used in the world. However, due to extensive use for many years, atrazine often appears in surface and groundwater. Atrazine transport is inhibited by degradation or sorption to soil components, especially organic matter. Biochar is a charcoal-like material produced from pyrolysis of biomass. Due to the amount and type of functional groups found on biochar, this product has shown potential for sorption of atrazine from solution. There is an interest in developing best management practices utilizing biochar to filter atrazine from non-point drainage with pollution-control structures such as blind inlets. The objective of this study was to explore the kinetics and thermodynamics of atrazine sorption to biochar using two different approaches: flow-through sorption cells and isothermal titration calorimetry (ITC). Twenty-five milligrams of an oak (Quercus spp.)-derived biochar was suspended in water and titrated 25 times (0.01 mL per titration) with atrazine at three different concentrations, and by a single titration (0.25 mL), with heat of reaction directly measured with ITC. A benchtop atrazine sorption study that simulated the titration experiment was also conducted. A continuous flow-through system was used to quantify the impact of contact time on atrazine sorption to biochar. Atrazine sorption to biochar displayed both exothermic and endothermic signals within each titration, although the net reaction was exothermic and proportional to the degree of sorption. Net enthalpy was −4,231 ± 130 kJ mole−1 atrazine sorbed. The existence of both exotherms and endotherms within a single titration, plus observation of an initial fast reaction phase from 0 to 300 s followed by a slower phase, suggested multiple sorption mechanisms to biochar. Results of flow-through tests supported kinetics observations, with the 300 s contact time removing much more atrazine compared to 45 s, while 600 s improved little compared to 300 s. Based on flow-through results, annual atrazine removal goal of 50%, and typical Midwestern U.S. tile drainage conditions, a pollution-control structure implementing this biochar sample would require 32 and 4 Mg for a design utilizing a contact time of 45 and 300 s, respectively. Future work is necessary for estimating degradation of atrazine sorbed to biochar.

Blind inlets: conservation practices to reduce herbicide losses from closed depressional areas

Purpose In a 6-year study, we investigated the effectiveness of blind inlets as a conservation practice in reducing pesticide losses compared to tile risers from two closed farmed depressional areas (potholes) in the US Midwest under a 4-year cropping rotation.

Atrazine Sorption by Biochar, Tire Chips, and Steel Slag as Media for Blind Inlets: A Kinetic and Isotherm Sorption Approach

Surface inlets are installed in subsurface drainage systems to reduce ponding duration and surface runoff, but can contribute to water quality concerns by allowing water to directly enter buried drains. Blind inlets consist of perforated pipes covered with gravel and are separated from an overlying sand layer by a geotextile membrane and have been shown to be more effective in reducing losses of sediment, nutrients, and pesticides than typical tile line risers. In this study, we investigated whether the effectiveness of blind inlets to sorb pollutants, with emphasis on the herbicide atrazine, could be further improved by amended them with materials other than limestone. The media, shredded tires (tire chips), electric arc steel furnace slag (steel slag), and oak-derived biochar were chosen because they are readily available, inexpensive, and do not present environmental concerns. Kinetic sorption and isotherms were determined to ascertain atrazine sorption by these materials, in addition to testing for potential metal leaching using the Synthetic Precipitation Leaching Procedure (SPLP) and the Toxicity Characteristic Leaching Procedure (TCLP). The kinetic data were fitted using pseudo first- and second-order reaction equations and indicated that atrazine sorption rate was 38 times faster and equilibrium was reached 5 times earlier for biochar than tire chips. The 24-h sorption isotherm data were fitted to the Freundlich sorption equation. The sorption coefficient for biochar was higher than for tire chips, steel slag, and limestone. Per the SPLC and TLCP tests, there was no leaching of heavy metals at levels of environmental concern. Our results suggested that the effectiveness of blind inlets as well as other conservation practices that include filter media such as rain gardens and filter socks could be improved by incorporating more reactive materials than sand and gravel with biochar being a particularly effective alternative.

Effect of replacing surface inlets with blind or gravel inlets on sediment and phosphorus subsurface drainage losses.

Open surface inlets that connect to subsurface tile drainage systems provide a direct pathway for movement of sediment, nutrients, and agrochemicals to surface waters. This study was conducted to determine the reduction in drainage effluent total suspended sediment (TSS) and phosphorus (P) concentrations and loads when open surface inlets were replaced with blind (in gravel capped with 30 cm of soil) or gravel (in very coarse sand/fine gravel) inlets. In Indiana, a pair of closed depressions in adjacent fields was fitted with open inlet tile risers and blind inlets in 2005 and monitored for flow and water chemistry. Paired comparisons on a storm event basis during the growing season for years 2006 to 2013 showed that TSS loads were 40.4 and 14.4 kg ha event for tile risers and blind inlets, respectively. Total P (TP) and soluble reactive P (SRP) loads were 66 and 50% less for the blind inlets, respectively. In Minnesota, TSS and SRP concentrations were monitored for 3 yr before and after modification of 24 open inlets to gravel inlets in an unreplicated large-field on-farm study. Median TSS concentrations were 97 and 8.3 mg L and median SRP concentrations were 0.099 and 0.064 mg L for the open inlet and gravel inlet periods, respectively. Median TSS and SRP concentrations were elevated for snowmelt vs. non-snowmelt seasons for open and gravel inlets. Both replacement designs reduced suspended sediment and P concentrations and loads. The Indiana study suggests blind inlets will be effective beyond a 10-yr service life.

Managing farmed closed depressional areas using blind inlets to minimize phosphorus and nitrogen losses

AbstractClosed depressions are sites within a landscape from glacial origin in which runoff water tends to collect because there is no natural outlet. When farmed, this water is often drained via a tile riser, a vertical tube that connects the bottom of the low point of a closed depression with the subsurface tile drainage network. Two field‐sized closed depressions (ca. 4 ha) and two small catchments (ca. 300 ha) were used to test the hypothesis that water quality could be improved by replacing tile risers with blind inlets, ca. 18 m2 holes filled to 1 m depth so that a high infiltration capacity was attained. At the field scale discharge, sediment and nutrient loads were lower when drained with the blind inlet compared to the tile riser. Late Spring 2010 was much wetter than normal, and increased nutrient loading was observed in both small catchments compared with previous years. In 2010, discharge and total P loading from Catchment AME (control catchment drained with tile risers) increased 417% and 737%, respectively, compared to the mean for the six previous years, whereas in Catchment BME (treatment catchment drained with blind inlets), there was only a 64% and 92% increase, respectively. Results from this study indicate that replacing tile risers with blind inlets to drain closed depressions may be one method to effectively reduce nutrient and sediment loading to Lake Erie and other sensitive water bodies that lie in landscapes formed by Wisconsin, Weichselian or Devensian glaciation.

Phosphorus and sediment loading to surface waters from liquid swine manure application under different drainage and tillage practices

Abstract Phosphorus (P) and sediment can move from agricultural land to surface waters, deteriorating its quality. This study was undertaken to improve understanding of partitioning of P and sediment to surface water via overland runoff and underground drainage pathways, and identify control measures. Over two full years, and including important winter events, P and sediment load overland and through tile were quantified from micro-catchments with relevant drainage and management practices imposed. Crop nutrients were supplied by liquid swine manure, either injected under minimum tillage management or surface-applied and incorporated under conventional till. Winters were temporally important for loadings from both runoff and drainage tile, particularly during rain on snow. A single event of 50 mm rain on snow over 2 days contributed more than 80% of the Pdop (dissolved organic + particulate P) and sediment that moved overland, and contributed 28% of Pdop and 20% of the sediment that moved through drainage tile during that season. Loads of P and sediment in both overland runoff and tile drainage were greater in non-growing seasons (NGSs) than growing seasons (GSs). For example, loading overland averaged 0.14 kg ha−1 dissolved reactive phosphate (DRP) and 1551 kg ha−1 sediment in NGSs, and 0.04 kg ha−1 DRP and 42 kg ha−1 sediment in GSs (four catchments, two seasons, runoff DRP first GS only). Through drainage tile, DRP load averaged 0.08 kg ha−1 in NGSs and 0.01 kg ha−1 in GSs from one field, A, and 0.02 kg ha−1 in NGSs and 0.003 kg ha−1 in GSs from another field, B; Pdop load was 0.07 kg ha−1 in NGSs and 0.02 kg ha−1 in GSs, similar from both Fields A and B; and sediment load was 23 kg ha−1 in NGSs from Field A, 8 kg ha−1 in NGSs from Field B, and 2 kg ha−1 in GSs from both fields. It is therefore important to manage movement during NGSs, particularly when runoff occurs over frozen soil. Movement through drainage tile comprised 31, 24 and 16% of the overland + subsurface DRP, total P (Pt) and sediment loads, respectively. Presence or type (blind inlet or hickenbottom) of surface inlet had little impact on P and sediment loading. Artificial drainage reduced overland + subsurface load to surface water to one-third for Pt and one-tenth for sediment, and is therefore a suitable strategy for controlling both P and turbidity in surface water. Overland + subsurface DRP load was unchanged by artificial drainage. Preferential flow of liquid swine manure to drainage tile only occurred with injection, in the year the drains were installed, in one of two fields. Along with being infrequent, the incidental DRP load through tile drains comprised only 2% of the annual Pt load from the catchment. The associated minimum tillage system reduced overland Pt and sediment runoff load 3- and 6-fold, respectively, relative to conventional till with broadcast incorporated manure.

Abstract: Nearshore Morphology and Sediment Characteristics Along Ward Island, Corpus Christi, Texas

ABSTRACT Texas A&M University-Corpus Christi is sponsoring a study on the feasibility of a recreational beach for its campus located on Ward Island. The beach would front the northern shoreline of Ward Island along Corpus Christi Bay, Corpus Christi, Texas. The functional design process provided an opportunity to investigate the nearshore morphology and sediment characteristics of this unstudied shore. Seasonal profile surveys were conducted from the spring of 1994 to the winter of 1996 and included sediment sampling along select transects. Repetitive profile surveys taken along the same transect proved average survey elevation accuracy to be better than 0.7 cm. The surveys extended the entire 2.6 km length of the northern Ward Island shoreline from the Oso Inlet to the Blind Oso Inlet. An unusually flat and wide nearshore region was identified. The shallow (1.1 m) nearshore typically extends 150-200 m offshore. The depth of closure, or active region of sediment transport, is at 1.6 m Mean Tide Level, as identified through profile surveys. The sediment in the nearshore is moderately sorted, inclusive graphic standard deviation of 0.02 mm, fine sand with a median grain size diameter of 0.14 mm. The survey defined a well-developed longshore bar system that was previously observed visually during periods of low tide and in aerial photographs. This system consists of four to seven sandbars that slowly migrated offshore during the study period, independent of season. Inspection of aerial photographs taken from 1934 to 1996 indicate that the number and linearity of longshore bars has decreased. In addition, the bars west of the Blind Oso Inlet appear to be superimposed on a raised subsurface feature. This plateau was also identified at Poenisch Park, located west of Ward Island, indicating that the sandy nearshore region is a veneer over a firm relic shelf. This study hypothesizes that the decrease in number and linearity of the longshore bar system is related to a decrease in sand resources. Thus, natural accretion of a beach along Ward Island is unlikely. Therefore sandy-fill material along with coastal structures will be necessary to provide a stable beach in this region.

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The newly published Conservation Practice Effectiveness (CoPE) Database compiles information on the effectiveness of a suite of conservation practices developed to treat contaminants in surface runoff and tile drainage water from agricultural landscapes. Traditional conservation practices such as no-tillage and conservation crop rotation are included in the CoPE Database, as well as novel practices such as drainage water management, blind inlets, and denitrification bioreactors. This will be particularly useful to conservation planners seeking new approaches to water quality problems associated with dissolved constituents, such as nitrate (NO₃) or soluble phosphorus (SP), and for researchers seeking to understand the circumstances in which such practices are most effective. Another novel feature of the database is the presentation of information on how individual conservation practices impact multiple water quality concerns. This information will be critical to enabling conservationists and policy makers to avoid (or at least be aware of) undesirable tradeoffs, whereby great efforts are made to improve water quality related to one resource concern (e.g., sediment) but exacerbate problems related to other concerns (e.g., NO₃ or SP). Finally, we note that the CoPE Database can serve as a source of the soft data needed to calibrate simulation models assessing the potential water quality tradeoffs of conservation practices, including those that are still being developed.

Phytoplankton Ecology of Vancouver Harbor

Phytoplankton production and distribution were examined over a 2-yr period in the Burrard Inlet system, which includes a true fiord (Indian Arm), a shallow blind inlet (Port Moody Arm), and a turbulent narrows region that is contiguous to the Port of Vancouver. Greatest annual production occurred in Port Moody Arm with a mean of 532 g C∙m−2∙yr−1 while the lowest values were in Indian Arm and the Narrows region, averaging about 260 g C∙m−2∙yr−1. Nitrate and zooplankton grazing were the main factors limiting phytoplankton production in Indian Arm, while flushing and poor light conditions influenced phytoplankton growth in the Narrows and outer Burrard Inlet. Most of the discharges of domestic and industrial wastes have been diverted to the Fraser River, and Vancouver Harbor can be considered relatively clean and pollution-free because of strong tidal mixing and seaward flushing. The only sign of eutrophication in the inlet is in Port Moody Arm where sufficient nutrients from sewage discharges and a relatively stable mixed-layer depth create near optimal conditions for phytoplankton growth. Daily production here is among the highest recorded in the literature for Pacific coastal marine waters. Key words: Phytoplankton, primary production, coastal marine embayment, fiord, phytoplankton succession and distribution, chlorophyll a