Filter Drain Research Articles

Highway filter drains: precursors for maintenance management

This paper conceptualises and presents a number of asset management building blocks required to establish holistic management for highway filter drains in the UK roads network. This is accomplished by evaluating current maintenance and management thinking and by identifying how existing strategies are lacking and potentially unsustainable. A condition assessment regime is hence described, tied to a measure of filter drain level of service (drainability) and an asset-specific ageing/renewal model that adopts six discreet condition bands is proposed. For this model to hold true, the Markov process is assumed to represent cumulative damage in a network. Drawing from relevant asset management concepts, a decision support tool to inform and optimise managerial decisions in respect to maintenance planning and resources allocation is also described.

Long-Term Metal Retention Performance of Media Filter Drains for Stormwater Management

Stormwater runoff, a substantial source of nonpoint pollution, can be treated using Best Management Practices (BMPs), such as the Media Filter Drain (MFD). An MFD is a trench filled with an engineered media mix, usually with a grass overlay, that receives runoff from the paved roadway next to it. The MFD was shown to remove dissolved metals (zinc and copper), typical pollutants from vehicles and urban areas, which might negatively impact aquatic species in receiving waters, but its long-term effectiveness was not known. Existing media filter mixes of different ages were collected from two different sites in the Pacific Northwest of the United States. Columns made with these media mixes received concentrated copper and zinc loading to simulate accelerated aging for estimated total lifespans from 14 to 22 years of copper and zinc loading, with little or no decrease in sorption. Throughout the aging process, some columns were subjected to performance testing with higher levels of typical runoff concentrations and average concentration decreases from influent to effluent were found to be greater than 90% for both copper and zinc. Based on this study, the MFD’s lifespan for zinc and copper treatment is significantly greater than the initial ten-year estimate.

Organized variability of surface runoff responses across neighboring hillslopes in Iowa

Summary Characterizing the spatial and temporal variability of small scale runoff responses is essential to distributed hydrologic modeling. To explore the variability of runoff responses, we analyzed surface runoff hydrographs from 12 neighboring hillslopes in central Iowa, USA that were observed for 72 runoff events over a four-year period. These agricultural experimental hillslopes receive various prairie filter strip treatments and drain areas ranging from 0.48 to 3.19 ha. The distances between them vary from tens of meters to about 3 km. We compared the hydrographs from the remaining 11 hillslopes to the hydrograph at the benchmark hillslope (i.e., hillslope B6 with no treatment). The results showed that: (1) for any individual event in which noticeable surface runoff occurred, the hydrographs from these hillslopes had similar shapes but different magnitudes; (2) for any paired hillslopes, the shape similarity persisted, but the scaling factor (the regression slope between two flow series) changed across events; and (3) for any runoff event, no simple relationship exists between the spatial variation of the scaling factor and the slope, slope length, area, and prairie strip width at the footslope of the hillslopes. Interestingly, we found that for 9 out of the 11 paired hillslopes, 40–70% of the temporal variation in the scaling factors can be explained by the antecedent wetness condition and the maximum hourly rain accumulation. These results suggest that the small-scale surface runoff responses are spatially variable but organized linearly, i.e., shape similarity (or linearity) in space is another feature of the small-scale runoff process. This phenomenon seems to result from the spatial vicinity and small-scale spatial variability of rainfall intensity and antecedent soil moisture.

Adequacy of Seepage Analysis in Core Section of the Earthen Dam with Different Mix Proportions

Earthen dams are built since early days of civilization. These dams constitute to be the most common type, because it is generally built of locally available materials which derive strength from their position, friction and cohesion. Many earth fill dams are vulnerable to failures due to seepage problems that take place in the core since all soils are pervious to a smaller or larger extent. One of the ways to control seepage problem in earthen dam is by using proper materials for core section since the core section of earthen dam provides impermeable barrier within the body of the dam. Thus, this paper analyses the usage of various materials with different combinations to zone type earthen dams with central impervious vertical core and to study the behavior of phreatic line at downstream phase by varying effective length of horizontal drainage filter. The results obtained from laboratory, proposed geometry of dam and corresponding stability analysis made for various materials showed that materials with impervious nature only provides safety to core part of the earthen dam

Chemical ageingaging of a polyester nonwoven membrane used in aerosol and drainage filter

The filter media in polyester is one of the most geotextile materials used in aerosol and drainage filtration, particularly for soil reinforcement in civil engineering due to its appropriate properties and its low cost. However, the current understanding of the durability and stability of this material in real service conditions, especially under severe long-term conditions are completely limited. This work presents an investigation of the chemical aging of a commercial nonwoven polyester membrane under different temperatures and pH environments in relation to its morphology, mechanical properties and molar mass. The results showed a significant reduction of mechanical properties in term of tensile strength, puncture resistance and tearing forces of the membrane after aging process due to the chemical degradation. The molar mass and mechanical properties changes with temperature and pH showed a complex dependence of material properties on environmental conditions. Based on the obtained results, the lifetime of the material at different temperatures was determined by the use of the Arrhenius model. These results provide useful information to a better understanding of phenomena occurring during chemical aging of the polyester nonwoven membranes and may help to predict the service lifetime of this material in conditions of use encounteredin service.

A three-step test of phosphate sorption efficiency of potential agricultural drainage filter materials

Phosphorus (P) eutrophication of lakes and streams, coming from drained farmlands, is a serious problem in areas with intensive agriculture. Installation of P sorbing filters at drain outlets may be a solution. Efficient sorbents to be used for such filters must possess high P bonding affinity to retain ortho-phosphate (Pi) at low concentrations. In addition high P sorption capacity, fast bonding and low desorption is necessary. In this study five potential filter materials (Filtralite-P®, limestone, calcinated diatomaceous earth, shell-sand and iron-oxide based CFH) in four particle size intervals were investigated under field relevant P concentrations (0–161 μM) and retentions times of 0–24 min. Of the five materials examined, the results from P sorption and desorption studies clearly demonstrate that the iron based CFH is superior as a filter material compared to calcium based materials when tested against criteria for sorption affinity, capacity and stability. The finest CFH and Filtralite-P® fractions (0.05–0.5 mm) were best with P retention of ≥90% of Pi from an initial concentration of 161 μM corresponding to 14.5 mmol/kg sorbed within 24 min. They were further capable to retain ≥90% of Pi from an initially 16 μM solution within 1½ min. However, only the finest CFH fraction was also able to retain ≥90% of Pi sorbed from the 16 μM solution against 4 times desorption sequences with 6 mM KNO3. Among the materials investigated, the finest CFH fraction is therefore the only suitable filter material, when very fast and strong bonding of high Pi concentrations is needed, e.g. in drains under P rich soils during extreme weather conditions.

Treatment of heavy metals by iron oxide coated and natural gravel media in Sustainable urban Drainage Systems

Sustainable urban Drainage Systems (SuDS) filter drains are simple, low-cost systems utilized as a first defence to treat road runoff by employing biogeochemical processes to reduce pollutants. However, the mechanisms involved in pollution attenuation are poorly understood. This work aims to develop a better understanding of these mechanisms to facilitate improved SuDS design. Since heavy metals are a large fraction of pollution in road runoff, this study aimed to enhance heavy metal removal of filter drain gravel with an iron oxide mineral amendment to increase surface area for heavy metal scavenging. Experiments showed that amendment-coated and uncoated (control) gravel removed similar quantities of heavy metals. Moreover, when normalized to surface area, iron oxide coated gravels (IOCGs) showed poorer metal removal capacities than uncoated gravel. Inspection of the uncoated microgabbro gravel indicated that clay particulates on the surface (a natural product of weathering of this material) augmented heavy metal removal, generating metal sequestration capacities that were competitive compared with IOCGs. Furthermore, when the weathered surface was scrubbed and removed, metal removal capacities were reduced by 20%. When compared with other lithologies, adsorption of heavy metals by microgabbro was 10-70% higher, indicating that both the lithology of the gravel, and the presence of a weathered surface, considerably influence its ability to immobilize heavy metals. These results contradict previous assumptions which suggest that gravel lithology is not a significant factor in SuDS design. Based upon these results, weathered microgabbro is suggested to be an ideal lithology for use in SuDS.

Reactivation of landsliding following partial cliff stabilization at Barton-on-Sea, Hampshire, UK

Abstract The historically unstable eastern side of the Barton Clay coastal outcrop was subject to stabilization works during 1967–1968, the principal part of which was a 1450 m long filter drain with a sheet pile cut-off aimed at the seepage-prone Barton Sand–Barton Clay junction. Subsequently four reactivated landslides occurred and by 2008 amounted to c . 46% of the total length of the filter drain. Two of these landslides were massive failures of the whole undercliff. This paper examines the relations between the landslides and the stratigraphy, including the presence of the known preferred surfaces of shearing, and the characteristic geomorphological modes of degradation in the Barton Clay undercliffs. It is shown that although the original drainage design reflected the influence of the stratigraphy, there was insufficient consideration of the hazards posed by the natural patterns of degradation and their geomorphological expression. The earlier two of the landslides were followed by remedial measures but the latest two are continuing. Although the cliff toe is well protected by a robust rock armoured revetment, the western end of this area is now reverting to the state that existed before the stabilization works were installed.

Measured and simulated effects of sophisticated drainage techniques on groundwater level and runoff hydrochemistry in areas of boreal acid sulphate soils

To abate the environmental problems caused by the severe acidity and high metal concentrations in rivers draining acid sulphate (AS) soils of Western Finland, control drainage (CD) and lime filter drainage (LFD), and their combination, were investigated. The effectiveness of these best management practices (BMP’s) on drainage water quality was studied on plot scale in two locations. In Ilmajoki, where the sulphidic materials are more than 2 m below the soil surface, CD efficiently reduced the concentrations of sulphate, aluminium, manganese and iron concentrations and to some extent also increased the pH of the drainage waters. LFD, in contrast, effectively reduced the drainage water acidity and raised the pH level. Decrease of the groundwater level owing to strong evapotranspiration in summer could, however, not be properly prevented by CD. In Mustasaari where sulphidic materials were as shallow as 1 m below soil surface, the positive effects of LFD recognised in Ilmajoki were hardly seen. This shows, that the tested BMP’s work properly, and can thus be recommended, for intensively artificially drained AS soils like in Ilmajoki where most of the acidity has already been transported to watercourses. LFD can, however, not be recommended for as yet poorly leached and thus particularly problematic AS soils like in Mustasaari. This is, of course, a drawback of the tested BMP, as it is not effective for the soils which would need it most. The field data were tentatively utilised to test the performance of the HAPSU (Ionic Flow Model for Acid Sulphate Soils) simulation model developed to estimate the loads of harmful substances from AS soils.;

Saturated-Unsaturated Flow through Leaky Dams

This research investigated seepage flow through leaky dams using the well known finite-element method. Different areas, locations, and hydraulic conductivities of leaks were examined. An area of leak, equal to 4.4% of the core area, increased the seepage flow through the dam to be about 9.5 times the seepage flow through tight (nonleaky) core. This happened for a dam having a downstream horizontal drainage filter. When the drainage filter did not exist, the increase of flow because of the same area of leak was about seven times the flow through a tight core. When the leak existed at the centerline of the core in the out-of-plane direction, its impact was slightly greater than when it existed at the edge of the core. Moreover, as the location of the leak moved up vertically, its impact was observed to be less. It was also observed that when the leak existed in curtain wall driven into underneath the dam, its impact was not significant compared with the case when it existed in the core.

Identification of sources and causes of leakage on a zoned earth dam in northern Taiwan: Hydrological and isotopic evidence

Abstract Seepage through an earth dam body must be regulated as a well–planned process, if it is not properly managed, the abnormal seepage may cause dam failure. This study employed stable isotopic and statistical methods to identify the source and cause of an abnormal leakage on the zoned earth dam of the Xin–Shan reservoir located in northern Taiwan. Water samples from the dam area over a 2-a period were collected and analyzed for their stable O and H isotope compositions. In addition, a 4-a period of hydrological data, including rainfall, reservoir level, well level, seepage of filter drainage and leakage, were statistically analyzed with a stepwise multiple regression approach. Both the stable isotopic and hydrological results indicate that the abnormal leakage on the dam shell comes from the filter drainage in the dam. The reason for abnormal leakage is due to unexpected and significant precipitation–sourced water flowing into the dam’s body. The dam filter fails to drain out the incoming water sufficiently, thus generating the abnormal seepage. In addition, the defect in the dam filter may also cause the drainage filter to drain off reservoir seepage inadequately. Therefore, it is suggested that checking the filter function and preventing excessive precipitation–sourced water from flowing into the dam are the two top priorities for the follow-up remedial strategy of the dam.

Highway filter drain waste arisings: a challenge for urban source control management?

Essential maintenance activities on highway BMP drainage controls involve refurbishment of filter (French) drains which can generate substantial amounts of "controlled waste". An innovative procedure for their re-instatement is described which offers a more sustainable option for filter drain/trench management. The quality classification of these waste arisings is problematical and it is difficult to reliably identify the risks posed by such materials and the most effective forms of management and disposal options.

Detection and evaluation of horizontal fractures in earth dams using the self-potential method

The self-potential method can be applied to evaluate the degree of water seepage into earth or rockfill dams. Spatial distribution of measured self-potential data can indicate possible anomalous water flow. Phenomena, such as piping, can be modelled as cylindrical bodies. Internal erosion can develop structures, which can be represented by a sphere or point source. Differential settlement in the dam structure occasionally creates horizontal fractures, which require equivalent geometrical body formula. An equation, which allows the calculation of a self-potential profile over a horizontal contact, was developed. This equation can also be applied to the inspection of water flow into horizontal drainage filters. When inverse interpretation returns bodies of relatively small amplitudes, then their probability can be tested statistically. A test, based on cross-correlation between a modelled curve and field data, can be used to evaluate their existence at a given probability level. An acceptance criterion is computed, using the concept of likelihood coefficient. The equation was applied to two case histories. The first is an example of water flow evaluation into a horizontal drainage filter. Several anomalous bodies were interpreted from residual self-potential data, i.e. from the difference between the theoretical response of the filter and the measured self-potential values, then, most of the interpreted bodies were statistically tested. The second case deals with detection and evaluation of a horizontal fissure. The interpreted parameters of the detected body corresponded well to a horizontal fracture found when the water level in the reservoir was lowered.

DESIGN OF HORIZONTAL FILTER LENGTH IN HOMOGENEOUS EARTH DAMS

ABSTRACT Earth dams are constructed to store or divert water. They are economical because they are constructed with locally available materials. A homogeneous section in an earth dam is adopted for low to moderate heights. A purely homogeneous dam section poses the problem of seepage leading to sloughing and piping if it is not quite wide at base. An earth dam can be prevented from the seepage failure by providing the filters. A filter can keep the top How line or phreatic line well within the body of dam. As the phreatic line follows a parabolic shape, there is some minimum length of downstream drainage filter to prevent the downstream slope from the softening due to seepage. Since earth dams are made of fine-grained soil, the softening may occur due to the capillary rise; hence an account for the capillary rise is necessary while calculating the minimum length of downstream drainage filter. Analytical solutions are not available for determining length of filter and downstream slope cover, though graphical solutions are available for them but they are long and involve personal skills and judgement. Explicit equations have been obtained in the present work for calculating downstream slope cover and length of downstream drainage filter. Similar equation has also been obtained for minimum effective length of drainage filter. These equations arc non-linear and representative graphs have been plotted for them covering all the practical ranges of the dam geometry.

Modeling Pavement Subdrainage Systems

A comprehensive study of pavement subdrainage systems was conducted. In the study, three test sections were constructed as part of a new bypass, I-469, at Fort Wayne, Indiana. Location of the drainage layer and materials for the bituminous base course and filter materials were varied from section to section. Instrumentation was installed in the three sections during construction and included sensors to measure temperature, frost, and moisture. Tipping bucket flowmeters were attached to the subdrainage system outlet pipes. A rain gauge was located at each section. A comprehensive laboratory testing program was conducted in the study. Hydraulic conductivity tests were conducted on subgrade, filter, pavement, and trench materials. In addition to conventional saturated permeability, moisture-suction tests were conducted on all materials to determine their partially saturated permeability. Movement of water through the three pavement sections was modeled by using the finite element method analysis. Laboratory-determined hydraulic properties of each material were input directly to the analysis. Several rainfall events were analyzed. Two events were used to verify the analysis model. Subsequent analyses were conducted on new events. Data were recorded for the three sections for 3 years. Measurements indicated that one of the three subdrainage sections drained in one-third the time of the other two sections. This was in agreement with the finite element method analysis. Also, a theoretical subdrainage section was analyzed by using optimal materials from all three sections. This optimized section was shown to further reduce the time of drainage. Conclusions and recommendations address drainage layer location, filter materials, material permeability, and collector pipe capacity.

Mid-1997 tidal surge of Bay of Bengal at Digha on the East Coast of India: Its damage evaluation and mitigation

The sea resort of Digha (21° 37' N: 87° 31' E) on the east coast of India runs the risk of natural disasters due to frequent development of atmospheric depressions in the bay of Bengal. A 3.7 km sea-wall (brick/concrete/boulder embankment) was built long back to protect the ENE-WSW coastline of this sea resort from erosion vis-a-vis wave action.
 An unusual tidal surge struck the Digha coast on 20 August 1997 causing extensive damage to the seawall, various structures within CRZ-11 and natural landscape. The Geological Survey of India (GSI) studied the cause and effect of this natural calamity. A deep depression was formed in the northern Bay of Bengal and the eye of anticlockwise circulation of wind from east to west became incremental with the attainment of minimum atmospheric pressure at the coast. The maximum wind speed was at 8:30 in the morning of 20 August 1997, which was second lunar day next to the full moon, and the highest spring tide was anticipated at 10:00. Besides, this was a period of autumn equinoctial tides when maximum tide raising forces were expected. This highest spring tide coupled with the easterly high velocity wind and prevailing longshore current of the sea towards ENE resulted in abnormal tidal surges for nearly one hour on 20 August 1997 (around 10:00). The sea at Digha otherwise attains an average of highest wave-crest height ranging between 3.5 m and 4.0 m above msl. The plunging breakers were reported to have risen that day 10 a wave crest height of about 6.4 m above msl and they overtopped the seawall upper level having 5.4 m of average Reference Level. About 378 million litres of seawater spilled over the wall and returned to the sea in just one hour's time by breaking the wall in the weak zones and adjoining structures. Geological parameters, measured in the natural selling of beach-coastline dunes, revealed marked changes in the magnitude of beach dimensions; lowering of beach front dune top by 2.46 m and erosion of the beach surface by 0.65 m constitute the direct fall out of this tidal surge.
 The GSI recommended both short- and long-term mitigation measures to minimise effects of such natural disasters. These included, interalia, a design of an ideal seawall with three consecutive foundation piles and one seaside sheet pile: lined drains to ease the surface runoff especially in case of overtopping by surges; provision for landslide filter drain and seaside geotextile apron, and systematic network of sewerage.
 As of now, the largely damaged part of the sea-wall has been newly laid by a 28.0 m wide concrete: ramp with 2.44 m deep sheet pile in the seaward side. Lined surface drain and impermeable filter drain of clay have been constructed behind the seawall. Raising of vertical height of the sea-wall and laying of sewerage network have also commenced. In addition, the proposal of laying geotextile mat in the unrestored part of the wall is on the anvil.

USE OF GRASSED BASINS TO FILTER RIVER WATER FOR SUBSURFACE IRRIGATION: SYSTEM DESIGN, CONSTRUCTION AND PERFORMANCE

Previous research in the St. Lawrence Lowlands, in the province of Québec, has shown that subsurface irrigation using subsurface drainage systems, increases the yield of maize and soybean by as much as 30%. However, to reach this goal and maintain the productivity of the system, the irrigation water must be free of sediments which could block the subsurface drain pipes. This paper presents the results of research on an economical means of filtering water for subsurface irrigation. It was found that grass filter basins are very efficient in removing sediment from river water. Grass filter basins having drain pipes in trenches 300 mm wide and backfilled with sand resulted in more than 90% of sediments being removed from the river water. It was found that the filtration system need occupy less than 0.2% of the area to be irrigated. In addition, filtration rates per unit area of filter basin and per unit length of filter trench and drain pipe, were also determined. River water was also filtered in basins covered with geotextile. Due to the fast clogging of the geotextile, this method was found to be impractical and expensive compared to filtration using water-tolerant grasses as basin covers.

Drainage efficiency of sand layer in layered clay-sand reclamation : Tan, S A; Liang, K M; Yong, K Y; Lee, S L J Geotech Engng Div ASCEV118, N2, Feb 1992, P209–228

A layered clay-sand-scheme was tested in a field trial. The thickness, permeabilities and the relative length of the flow path for the two materials was found to influence the drainage efficiency of the sand layer, which acts as a drainage filter. The extent of this influence is investigated in this study with reference to the drainage efficiency of the sand layer in a layered clay-sand scheme. The results are then used to evaluate the drainage efficiency in two field projects using the layered scheme. The details of the study are described, and the findings are discussed. It was found that the drainage efficiency was characterized by the permeability and flow-length ratios of the sand and clay in conjunction with the ratio of sand thickness to its horizontal length.

Closure of an Unlined Evaporation Pond: a Case History

In 1985, the Fort Worth District, Corps of Engineers, successfully permitted and executed the closure of an unlined evaporation pond at the Longhorn Army Ammunition Plant in east Texas. The pond, constructed in 1963 at the site of an active explosive waste-burning ground area, had been used to store explosive wastes resulting from the washout of rocket motor casings and solvent residues from operations involving pyrotechnic material preparation and mixing. Because operation of the unlined evaporation pond appeared to be primarily responsible for locally contaminating the ground water, the Army ceased operation of the pond in 1984 and began formal closure activities for the unit as a Resource Conservation and Recovery Act (RCRA) interim status surface impoundment. Under Phase I of the closure contract, a total of 1,877,113 gal of wastewater was removed and shipped via tank truck to a permitted disposal well some 80 mi from the site. The Phase II contract consisted of removal and transporting of contaminated sludges and soils to a permitted hazardous waste disposal site, backfilling the pond, installing a filter drain system, and turfing. A total of 8,116 yd 3 of material was excavated and shipped from the site.

Soil water flow model with two‐dimensional automatic gamma ray attenuation scanner

This paper describes a physical laboratory model to study two‐dimensional transient water and solute transport in unsaturated soil, including water uptake by roots. It features an automatic two‐dimensional gamma ray attenuation scanner for measuring soil water content. Automation is obtained with a simple closed loop control circuit. After a gamma count is transmitted to the teletypewriter, a signal is sent to the hydraulically moved scanner to search for the next grid point. Upon arrival the scanner sends a signal back to initiate another data acquisition sequence, and so on. In this way, synchronization between counter and scanner is assured independent of counting time, travel time, configuration of grid points, temporary slowdown, etc. It also eliminates dead time between grid points for any recording pattern. Grid points are established by an array of holes that trap the core of a solenoid actuator. The configuration of grid points can be changed easily by opening and closing the desired holes. This mechanical trapping was found to be simpler and more accurate than a potentiometric control. The soil water flow model is constructed in modules. It can be used as one unit of 3.15 by 1.07 by 0.178 m and inclined up to 30°, or it can be subdivided into up to eight compartments, each with its own drainage filter tubes. The front glass walls allow visual observations of soil packing, wetting fronts, root distribution, etc. The back aluminum walls allow installation of instruments, such as tensiometers, salinity sensors, and psychrometers.