METHOD FOR DESIGNING A DRAINAGE WELL NETWORK PATTERN AND CONCEIVING SAME

TECHNICAL FIELD

The present disclosure generally relates to soil science and agronomy, and more particularly to the draining of soils using vertical drainage wells and constructing same. The present disclosure also generally relates to soil amendments for vertical drainage wells.

BACKGROUND

Excessive water accumulation can cause complications in both urban and rural settings. In an agricultural context, water saturation of the soil surface and subsurface (i.e., at depth) may flood crops, asphyxiate roots thereof, or carry away nitrogen, thus negatively affecting crop productivity. The issue of improper soil aeration can be aggravated by, for instance, the contemporary and now widespread use of heavy agricultural machinery which has the secondary effect of further compacting the soil. Indeed, compacted soil layers or low hydraulic conductivity soil can impede subsurface drainage. At depth, a compacted subsoil layer creates a horizontal distribution of water, with the appearance of a perched water table near the topsoil, difficult to drain and problematic for plant growth, as previously mentioned. In addition, a compacted subsoil layer hinders water infiltration and channel runoff towards surface drainage channels, erosion gullies, and ditches, instead of favoring its vertical movement to recharge groundwater.

Various methods and processes exist to increase surface drainage and subsurface drainage efficiency. For surface drainage, some existing systems include cut-off drains, draining trenches, leveling the land to intercept and drive away runoff water toward streams and waterways. For subsurface drainage, some existing systems comprise drain tiles arranged at different horizontal distances and depths in the soil profile to be drained, some in an effort to bring down the level of the water table. However, such systems can prove to be prohibitive and inefficient because they scarcely consider characteristics such as a compacted soil profile, characteristics related to soil aeration, and spatial variability and distribution of these properties across the landscape. To overlook key soil factors may result in missed opportunities to offer an appropriate and efficient drainage solution for a given area to be drained. Among such soil parameters, soil air-filled porosity and gas diffusivity, for instance, have been shown to have a significant impact on plant growth. However, in-depth soil characterisation preceding the installation of drainage systems has often been scoffed as being time-consuming, costly, complex to sample, measure, and implement. Therefore, there is thus still a need for an improved drainage design method for soil surface and sub-surface.

BRIEF SUMMARY

According to an aspect, there is provided a method for designing a drainage well network pattern for liquid (water) drainage and constructing same, the method comprising: performing a preliminary soil characterization in a selected area to be drained. The preliminary characterization includes soil measurements sampled from the soil in the selected area at different locations thereof. The soil measurements include saturated hydraulic conductivity and one of soil total porosity, bulk density, air-filled porosity and gas diffusion measurements at different depths of the soil in the selected area; and using the preliminary soil characterization, generating the drainage well network pattern, including determining parameters of drainage wells to be constructed including a spatial distribution and determining parameters of drainage depth and radius of the drainage wells.

According to an implementation, there is provided that the at least one soil measurement of the preliminary soil characterization includes a plurality of soil measurements sampled from the soil in the selected area at different sampling point locations thereof.

According to an implementation, the method further includes drilling a plurality of holes into the soil of the selected area based on the generated drainage well network pattern.

According to an implementation, there is provided that the at least one soil measurement of the preliminary soil characterization includes a pH measurement.

According to an implementation, using a result of the preliminary soil characterization to generate the drainage well network pattern further includes determining a particulate material for filling at least one of the drainage wells and filling at least one of the plurality of drilled holes with the determined particulate material.

According to an implementation, there is provided that the particulate material has a granulometry in a range of about 0.10 mm to about 20 mm.

According to an implementation, there is provided that the particulate material has a composition comprising soil particulate and organic matter, and wherein a concentration of the organic matter in the particulate material is of about 15 volume per volume to about 100 volume per volume.

According to an implementation, the method further includes gathering at least a portion of the particulate material within a distance of about 50 km of each of the plurality of drilled holes.

According to an implementation, there is provided that the concentration of the organic matter in the particulate material is of about 50 volume per volume to about 100 volume per volume when the soil particulate includes a soil having at least about 30 of clay content per volume.

According to an implementation, the determining parameters of drainage wells and the determining of the particulate material comprises determining the parameters of the drainage wells and the composition of the particulate material to maintain a minimum gas diffusion of 0.03 in the selected area.

According to an implementation, there is provided that the organic matter of the particulate material comprises at least one of plant seeds and plant cuttings.

According to an implementation, the method further includes providing a pre-filled log including a tubular sheath having a membrane wall defining a core comprising the organic matter of the particulate material. There is also provided that the method further includes filling the at least one drainage wells by inserting the pre-filled log into the plurality of holes.

According to an implementation, the membrane wall of the tubular sheath comprises a natural fiber netting.

According to an implementation, the membrane wall of the tubular sheath comprises a rigid or semi-rigid mesh.

According to an implementation, there is provided that using a result of the preliminary soil characterization to generate the drainage well network pattern further includes determining a soil additive mixture for filling at least one of the drainage wells and promoting plant growth about the drainage wells. Further, the soil mixture additive comprises at least one of a plant fertilizer and a soil conditioner.

According to an implementation in which the selected area has a heterogeneous soil having a plurality of substantially homogeneous soil strata, and in which the spatial distribution of the drainage wells comprises a plurality of densities, each of the plurality of densities is adapted for a respective substantially homogeneous soil stratum.

According to an implementation, there is provided that the depth of the drainage wells is greater than a minimal depth and smaller than a maximal depth, such that the minimal depth corresponds to a depth of a compacted layer in a soil profile at a respective location according to the spatial distribution, and such that the maximal depth enables a capillary rise of soil liquid upwardly in the drainage wells.

According to an implementation, determining parameters of drainage wells to be constructed further includes a total volumetric dimension corresponding to an average rain runoff in the selected area.

According to an implementation, the method further includes inserting an elongated sleeve in at least one of the drainage wells to stabilize peripheral walls thereof. There is also provided that an upper end of the elongated sleeve is located at a depth of at least 25 cm from the soil surface.

According to an implementation, there is provided that the elongated sleeve comprises metallic material detectable by metal proximity sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a method for designing a drainage well network pattern and conceiving same, in accordance with an implementation;

FIG. 2 is a schematic map showing a selected area and sampling points distributed across the selected area according to a systematic sampling plan, in accordance with an implementation of the method;

FIG. 3 is a schematic map of the selected area shown in FIG. 2, showing sampling points distributed according to a random stratified sampling plan, in accordance with another implementation of the method;

FIG. 4 is a schematic of a cross-section view of soil layers of the selected area shown in FIGS. 2 and 3 along a section line, having a heterogeneous soil profile, and showing different sample depths at a sampling point, in accordance with an implementation;

FIG. 5 is a schematic of a cross-section view of soil layers of the selected area shown in FIGS. 2 and 3 along a section line, having a homogeneous soil profile, and showing a plurality of vertical drainage wells, in accordance with an implementation;

FIG. 6 is a schematic of a cross-section view of soil layers of the selected area shown in FIGS. 2 and 3 along a section line, having a heterogeneous soil profile, and showing a plurality of vertical drainage wells, and each drainage well having a different depth, in accordance with an implementation;

FIG. 7 is a schematic of a cross-section view of soil layers of the selected area shown in FIGS. 2 and 3 along a section line, having a heterogeneous soil profile, and showing two vertical drainage wells, in accordance with an implementation;

FIG. 8 is a schematic of a cross-section view of soil layers of the selected area shown in FIGS. 2 and 3 along a section line, and showing a water table at two drawdown stages, in accordance with an implementation;

FIG. 9 is a graph showing values of soil gas diffusivity as a function of soil air-filled porosity, and corresponding water head pressure (or soil water potential) in accordance with a soil type;

FIG. 10 is a graph showing values of unsaturated soil conductivity as a function of water pressure head, in accordance with a soil type; and

FIG. 11 is a schematic of a cross-section view of a soil layer of the selected area shown in FIGS. 2 and 3 along a section line, having a homogeneous and permeable soil profile, and showing a vertical drainage well, in accordance with an implementation.

DETAILED DESCRIPTION

As will be explained below in relation to various implementations, the present disclosure describes a method for designing a drainage well network pattern and conceiving said network for improving surface and subsurface drainage of soil, such as in agricultural soils. More particularly, the present disclosure relates to a method for determining a depth, a diameter and a spatial distribution of drainage wells as part of a drainage well network to improve and, in some implementations, optimize soil liquid drainage according to the specifications of a selected land area, and to reduce costs associated therewith.

It will be noted that the terms “drainage well”, “vertical well” or “vertical drain”, as may be used herein, are to be understood as any vertical underground structure that disposes of unwanted surface and/or subsurface liquid phase that is gravity-fed, then stores and/or gradually infiltrates said liquid phase into a groundwater aquifer or subsoil layer. It will also be noted that the term “depth”, as may be used herein, is to be understood as a vertical distance between a level of the exposed soil surface and an element in the subsoil. In some embodiments of the method described herein in which the soil profile is highly permeable, the “drainage wells” may include “horizontal wells”, located below a top surface, that are integrated to increase drainage to a sufficient degree.

In this specification, the terms “soil liquid”, “soil liquid phase”, and “water” are used interchangeably and are intended to mean the liquid phase contained in the soil, which mainly includes water but also includes other organic and inorganic solutes, micro-organisms, and colloids.

The method for designing a drainage well network pattern and conceiving said network can be implemented by performing a preliminary characterization of the soil in the selected area of interest where drainage is needed. As part of the preliminary soil characterization, saturated hydraulic conductivity of the soil is measured at one or several different depths. Also, as part of the preliminary soil characterization, at least one of soil porosity and soil aeration (i.e., air-filled porosity and/or gas diffusivity) is measured or estimated. It is noted that other soil characteristics can be measured and included in the preliminary characterization to refine a diagnosis of the soil and thereby increase the efficiency of the drainage wells of the network.

Once the preliminary soil characterization completed, the information gathered can be used to determine a spatial distribution and/or density of the drainage wells to be constructed and dimensions thereof, including a determined depth and a determined diameter, and a particulate material to fill the drainage wells at different coordinates. Then, holes can be drilled and constructed using a result of the generated drainage well network pattern to drill and arrange a plurality of said drainage wells into the soil in the selected area, such that the drilled holes can be configured into drainage wells for drainage. Finally, the drilled holes of the network can be filled with the particulate material which can be gathered and processed about the selected area and has a granulometry in a range of about 0.10 mm to about 20 mm.

According to one aspect, the method can be used to drain the selected area at a sufficiently rapid rate to obtain a water table drawdown rate of about 30 cm to about 40 cm per day—or a slower rate (e.g., about 5 cm to about 10 cm per day) if needed for some crops or land of lower values—and a more uniform water table. In contrast, it should be noted that while a drainage well should provide an appropriate infiltration rate at the top surface, an excessive drainage rate should be avoided at the bottom of the drainage well to allow for an adequate temporary water table to form and provide sufficient bottom-up capillary rise (i.e., vertical suction and/or capillary suction) from the drainage well to the top surface 20 for several days to take place thereafter, as shown in FIG. 7. According to another aspect, the method can also be used to maintain an appropriate water table level by adjusting the drainage well depth to lower the water potential (e.g., more than about 40 cm of depth) to enable proper oxygenation of the surface layer. By carefully choosing a filling material specified further below, the dimensions and a spacing of the drainage wells, the drawdown, the oxygenation and the capillary rise of the soil in the selected area 10 can be improved.

It should also be understood that drainage wells and drainage trenches are designed to rapidly eliminate the free water that forms on the topsoil and to channel it into a drainage system so that the soil liquid (water) can be redistributed in the soil profile, either for irrigation in dry soils, or for deep drainage in wet soils to increase the top layer 22 gas diffusivity for better plant growth. It will be noted that the term “drainage system”, as may be used herein, is to be understood as the collective drainage infrastructure present in the subsoil, including: drainage wells of the drainage well network pattern, pre-existing wells, drainage trenches and horizontal drains pipes 50 (as shown in FIGS. 4 to 7), for instance.

With reference to FIG. 1, a schematic of an implementation of a method for designing a drainage well network and conceiving said network 100 is shown. In this aspect, steps of the method 100 can be carried out using a processing unit (such as a computer or portable device) or calculated by hand. The method 100 can include the following:

- (101) performing a preliminary characterization of the soil in a selected area 10 to be drained, wherein the preliminary characterization includes at least one soil measurement sampled from the soil in the selected area 10 at one or more sampling location 12 thereof, which can include a determined location, and wherein the at least one soil measurement includes saturated hydraulic conductivity and at least one of soil air-filled porosity and gas diffusion measurements at one or more depths of the soil, which can include a determined depth, in the selected area 10;
- (102) using information from the preliminary soil characterization (101), generating the drainage well network pattern, including determining dimensions and positions (i.e., spatial distribution) of a plurality of drainage wells 60 to be constructed, and a particulate material filler 70 (the “particulate material” 70, or “particulate filler” 70), which can include a determined particulate material 70 selected according to a granulometry and a composition;
- (103) using a result of the generated drainage well network pattern (102), drilling a plurality of holes into the soil according to the determined spatial distribution, such that the plurality of holes is configurable into the plurality of drainage wells 60; and
- (104) filling the drainage wells 60 with the determined particulate material 70, which can be at least partially composed of material gathered about the selected area 10, wherein the particulate material 70 gathered is selected according to a granulometry, for instance in a range of about 0.10 mm to about 20 mm.

Regarding the preliminary characterization (101) of the method 100, the method 100 involves the selection of an area of interest where drainage is needed or expected (the “selected area” 10). In the process of delimiting the selected area 10, one may exclude areas that are known to be exempt from drainage issues or that are outside of the purview of the relevant land owner or farm operator 18, as represented in FIGS. 2 and 3. It will be noted that before the preliminary characterization of the soil 101 can be performed, the selected area 10 can be surveyed with methods and tools well known in the art of soil science and/or agronomy, such as GPS topography and laser graders, to assess land topography and the risk of ponding (i.e., retention pools).

If the land survey reveals excessive water/liquid accumulation on the soil surface 20, surface levelling of the selected area 10 preceding or following the preliminary soil characterization 101 can be applied to level the soil surface 20 and/or install surface drainage channels since subsurface drainage is difficult to improve on without a degree of control on surface drainage.

It will be noted that land surveys can be performed with lidar imagery, time domain reflectometry and similar remote or proximal sensing technologies, or any process known in the fields of agronomy, land surveying, and hydrology.

Referring to FIGS. 2 to 4, once the selected area 10 is defined, measurements from soil samples, such as 40a, 40b, 40c in FIG. 4, in the selected area 10 can be carried out at different locations thereof 12 (i.e., the “sampling points” 12). The location of the soil sampling points 12 and the variability of sampling densities can be guided by field observations, satellite imagery, feedback from the land owner or farm operator, crop uniformity data (i.e., yield monitor data measured with yield sensors), a land survey with tools such as Veris, TDR, electromagnetic sensors and penetrometers, and any other relevant information to identify areas that may be poorly drained 16. Depending on different factors, the soil sampling can be carried out in accordance with a sampling plan; for instance, with one of a stratified sampling plan or a systematic sampling plan. As illustrated in FIG. 2, the systematic sampling plan consists in selecting sampling points 12 equally spaced so as to fully cover the selected area 10, but its validity should be verified. As illustrated in FIG. 3, the random stratified sampling plan consists in subdividing a heterogeneous land area into more homogeneous, mutually exclusive, and collectively exhaustive sub-populations (i.e., strata). Within each stratum, sampling points 12 are drawn randomly and independently. Still in accordance with the stratified sampling plan, the number of sampling points 12 may be identical between strata or proportional to the size of each stratum. Therefore, the locations for soil sampling, i.e., the sampling points 12, can be predetermined according to a systematic sampling plan (FIG. 1) or a stratified sampling plan (FIG. 2). If a lack of soil uniformity, drainage, or crop performance is observed or reported in the selected area 10, then a stratified sampling to scout zones with different hydraulic behaviours may be preferable. In contrast, if no preliminary information is available about the selected area 10, then a systematic sampling plan may be preferable to fully cover the soil surface to be characterized. For example, as illustrated in FIGS. 2 and 3, well drained zones 14 may show good performances, poorly drained zones 16 may have lower yields, while the zone outside of the selected area 18 may simply not be cultivated because of severe limitations (e.g., presence of stones, slopes, access cut). Finally, in a selected area 10 where yield or other limitations are not well known, sampling points 12 chosen according to the systematic sampling plan may be preferable. Other sampling plans are also contemplated herein, such as a simple random sampling procedure, for instance.

Once the soil sampling points locations 12 are determined, for instance according to a sampling plan, at least one soil parameter may be selected as part of the preliminary soil characterization (101) at different depths. As for the soil samples, their sampling depths can be predetermined. It is understood that where soil characteristics from the selected area 10 are known, for example from a previous unrelated soil characterisation process, the existing soil characteristic data can be integrated to the method 100 and thus reduce the number of samples collected at various sampling point locations 12. As better illustrated in the non-limiting schematic of a soil cross-section taken at a sampling point 12 of FIG. 4, soil samples 40a, 40b, 40c can be extracted from a sampling point 12 at different depths (d1, d2 and d3, for instance). For the sake of simplicity and in view of providing an implementation, the schematic of FIG. 4 exemplifies a generic agricultural soil profile displaying three characteristic layers 22, 24, 26, including a horizon surface layer 22 (i.e., arable layer 22, or top layer 22), a compacted layer 24 and a drainage layer 26 (i.e., water table zone 26). It is understood that soil samples 40a, 40b, 40c are collected in a similar manner in the presence of a more uniform soil profile in accordance with the method 100.

Still referring to FIG. 4, the three characteristic soil layers 22, 24, 26 of the soil profile can be identified through visual observation of the layers having contrasting bulk densities, with methods and tools well known in the art of soil science and agronomy (e.g., using a soil sampling auger, penetrometer, georadar, etc.). It will be noted that at the outcome of the visual observation of the layers, the sampling depths (d1, d2, d3) can be adjusted, for instance from about 80 cm to about 120 cm or more with regard to the drainage layer. In one implementation, bulk density can be measured in the aforementioned layers to conclude to the presence of a compacted layer 24, or lack thereof. Generally, the top layer 22 is situated between about 0 cm and about 25 cm of depth from the soil surface 20, but the top layer 22 can extend deeper in some instances, sometimes up to 35 cm. The compacted layer 24 is generally found at a depth of between about 25 cm and about 40 cm from the soil surface 20. The term “compacted soil layer” 24, as used herein, describes a soil layer that has lost some or most of its initial characteristic pore space and beneficial structure. Finally, the drainage layer 26 is situated between about 80 cm to about 120 cm from the soil surface 20. In the implementation shown, the first, second and third samples 40a, 40b, 40c can be taken at respective depths of d1, d2 and d3 such that the three characteristic soil layers 22, 24, 26 are represented in the preliminary soil characterization (101). Furthermore, even though this disclosure provides an implementation of three soil samples 40a, 40b, 40c—one for each layer in a compacted soil profile-a greater number of samples is envisioned for each layer profile and/or sampling point 12, for greater accuracy and drainage efficiency of the method 100. Also, in a naturally compacted layers profile in which the compaction of the soil can be more severe and extend deeper, it may be required to withdraw multiple samples located even deeper in the profile in relation to the previously mentioned sampling depths. Inversely, a smaller number of sampling points 12 or sampling depths is envisioned according to another implementation of the method 100. For example and without being limitative, the drainage method 100 can be executed from a single soil sample 40b, taken at sampling point 12 and extracted at one sampling depth d2 from the compacted layer 24, for example. It is appreciated the single soil sample can be taken from the soil surface 20 or the drainage layer 26.

From the soil samples 40, soil parameters can be measured or estimated. According to one non-limitative implementation, saturated hydraulic conductivity is measured at different depths, for instance at about 10 cm to about 20 cm, at about 20 cm to about 50 cm, and at about 60 cm to about 90 cm from the soil surface 20 (respectively represented by d1, d2 and d3 in FIG. 4). It is understood that, to perform efficient drainage via drainage well digging, an accurate knowledge of soil saturated hydraulic conductivity is required. According to one implementation, to account for soil aeration, at least one of gas diffusion (i.e., soil gas diffusivity), respiration rate, and soil porosity (i.e., air-filled porosity) is measured at different depths, for instance at about 15 cm and about 30 cm from the soil surface 20 (respectively represented by d1 and d2 in FIG. 4). In some instances, soil characterization is conducted at depths of between about 1.2 m to about 2 m, i.e., below the expected drain tile depth to verify whether there is a possibility that water can ascend therefrom and affect drainage. According to another implementation, and in view of providing a drainage well network pattern resulting in more efficient drainage, other soil parameters can be measured or estimated at different depths, such as moisture content, bulk density, the water desorption curve, and the alpha parameter (a). The parameters related to hydraulic conductivity, bulk density, the water desorption curves, and soil aeration, such as air-filled porosity and gas diffusivity, can be measured later by extracting samples to be analyzed in an off-site laboratory or directly on-site, for example by inserting probes at different depths in the ground, or by driving cylinders at different depths that perform a series of pumping and gas injection operations, see, for instance, DANE, Jacob H. et TOPP, Clarke G. (ed.). Methods of soil analysis, Part 4: Physical methods. John Wiley & Sons, 2020, or any other process known in the art. Other parameters can also be measured directly in the field or from samples taken to the laboratory such as iron, manganese, salinity, texture and particle size distribution, and any combinations thereof.

Still referring to FIG. 4, according to one non-limitative implementation in which a plurality of soil samples are taken at a sampling point 12 for preliminary soil characterization (101), a first sample 40a is collected in the arable layer 22 at about 15 cm to about 25 cm of depth (about d1) from the exposed soil surface 20, from which each of saturated hydraulic conductivity, the water desorption curve, the bulk density, and at least one of the respiratory rate, soil air-filled porosity and gas diffusion is either measured or estimated. A second sample 40b is collected, this time in the compacted layer 24 between about 25 cm to about 40 cm of depth (about d2), from which each of saturated hydraulic conductivity, the water desorption curve, bulk density, and at least one of respiratory rate, soil air-filled porosity, and gas diffusion are either measured or estimated. A third sample 40c is collected in the drainage layer 26 at a depth of between about 60 cm to about 90 cm (about d3) characterized by the presence of a water table 32, from which each of saturated hydraulic conductivity, the water desorption curve and the bulk density are either measured or estimated. Finally, a fourth sample can be taken below the expected drain tile position at about 1 m to about 2 m of depth, as previously mentioned, to estimate saturated hydraulic conductivity.

The literature in soil science, agronomy and hydrology shows that gas diffusion of at least about 0.03 to about 0.038 (i.e., the “minimum gas diffusion”) indicates a level of gas exchange processes within the soil favorable to plant and microbial growth, see, for instance, Chamindu, D. T., Clough, T. J., Thomas, S. M., Balaine, N., & Elberling, B. (2019). Density effects on soil-water characteristics, soil-gas diffusivity, and emissions of N20 and N2 from a re-packed pasture soil. Soil Science Society of America Journal, 83 (1), 118-125. This said, a different target value of gas diffusion can be selected depending on the crop used and other factors. Again, for the sake of simplicity and for providing an implementation, the rest of the disclosure provides a minimum gas diffusion of 0.03.

If the gas diffusivity or the air-filled soil porosity, and the moisture content are measured, a maximum moisture content from the drainage well network pattern required to maintain a minimum gas diffusion of 0.03 for a given soil layer at a given sampling point 12 can be determined. In other words, using methods and/or conversion tables known in the field of soil science and agronomy, the maximum moisture content in the soil required to maintain the minimum relative gas diffusivity of 0.03 can be calculated or converted from real time gas diffusivity and available moisture content. It is understood that if the air-filled porosity is measured instead of gas diffusion, gas diffusion can also be deduced therefrom using conversions methods known in the arts of agronomy and soil science, such as the Penman equation expressed by D_p/D₀=0.668, wherein & is air porosity.

Regarding generating the drainage well network pattern using a result of the preliminary soil characterization (102), the preliminary characterization of the soil (101) in the selected area 10 from at least one sampling point 12 is used. The drainage well network comprises one or more parameters of the drainage wells 60 to be constructed including at least one of determined dimensions of the drainage wells 60 and a spatial distribution and/or density of the drainage wells 60. The determined dimensions may include a drainage well depth and, if needed, a well diameter. Moreover, according to one implementation, a particulate material 70 to fill the drainage wells 60 is integrated to the drainage well network, for which its composition, hydraulic properties, and its granulometry are at least partially determined.

As mentioned, the determined dimensions and particulate material filler 70 of the drainage wells 60 of the drainage well network are determined such that sufficient liquid (water) infiltration and capillary suction are achieved. The dimensions, spatial distribution and particulate material filler 70 can be determined with one of the models and analytical tools well known in the fields of soil science, agronomy, and hydrology, such as, but not limited to, HYDRUS™ 2D/3D, SEVIEW SESOIL™, MODHMS™, MODFLOW-SURFACT™, and FEFlow™.

In one implementation, the diameter of the drainage wells 60 (or the drainage well hole) is dictated by the drilling equipment available and is therefore imposed, such that only drainage wells depth and the implementation thereof are to be determined by the method 100. According to another implementation, the diameter of the drainage wells 60 is selected as a function of the type of soil at the sampling point 12.

According to one aspect, a minimal depth and a maximal depth of the plurality of drainage wells 60 can be determined before determining the drainage well implementation and determined depth according to the drainage well network in a compacted soil profile, when necessary. According to one implementation, the minimum depth for each drainage well 60 is such that the compacted layer 24 for a given location provided by the determined spatial distribution is perforated so that the soil may be aerated by lowering the liquid (water) level at the bottom of the drainage well 60. The perched water table 30 then moves from the perforated position in the compacted layer 24 to the bottom of the well 60 and will therefore drain the surface soil 20 to increase its aeration by maintaining a sufficiently low water content and soil water potential for adequate gas diffusion in the top layer 22. All the drainage wells, shown in FIG. 6, are characterized by a depth greater than the minimum depth, thus enabling the vertical wells to perforate through the compacted layer 24 and the perched water table 30 according to the implementation described. It should be noted that the perched water table 30 represented in FIG. 6 has yet to dissipate downwardly despite the drainage wells 60. According to another implementation, the maximal depth for each drainage well 60 is such that a capillary rise of soil liquid (water) may occur therein to supply water upwardly, i.e., “bottom-up” (represented by an arrow in FIG. 7). Then, the maximal and minimum drainage well depths can be considered when determining the drainage well 60 depth, as ultimately generated by the drainage well network pattern, such that the drainage well 60 depth stays between the maximal and minimum values thereof.

Because the drainage wells 60 should provide appropriate surface drainage, in addition to subsurface drainage, the total volume of the plurality of drainage wells 60 can be sufficient to evacuate an average rain runoff in the selected area 10, according to one implementation. The assessment of average rain runoff volumes is made with tools and methods well known in the fields of hydrology, such as stormwater hydrographs and prediction models for peak runoff rates or available local weather records. The corresponding drainage well 60 volumetric dimensions ensure sufficient water runoff absorption therein and can be established using the depth and radius of the drainage well and the density such that the plurality of wells 60 can store a given runoff of about 1 cm to about 6 cm within two hours, for example. An analytical approach adapted to the soil profile in the selected area 10, as is known in the art, is described hereinafter.

According to one implementation, the depth of the drainage wells 60 of the drainage well network is adjusted depending on whether the soil at a given sampling point 12 is generally characterized as having adequate drainage or poor drainage. It will be noted that the determination of whether the soil has a poor drainage or an adequate one is made based on the distribution of saturated hydraulic conductivity at different positions in the profile with at least one being less than 1 m per day in at least one layer. A second criterion may be linked to aeration conditions, air-filled porosity, or the observed water potential or moisture content in the top layer 22. Measuring gas diffusivity directly in the top layer 22 indicates prevailing conditions. Other measurements can be made to indirectly gauge aeration: bulk density allows to calculate total porosity, and subtracting the volumetric water content from total porosity gives air-filled porosity. In the same vein, water potential (i.e., matric potential or pressure head) readings can be converted to a volumetric water content using the water desorption curve, and volumetric water content can be subtracted from total porosity to obtain an estimate of air-filled porosity. These parameters can be used as indicators of drainage and aeration problems that can benefit from corrections prescribed by the method 100. Referring to FIGS. 5 and 6, there is shown illustrations of different configurations of drainage wells 60 in a selected area 10 depending on whether the soil has appropriate or poor drainage, respectively. First, in FIG. 6, representing a compacted soil layer 24, there is shown a first drainage well 60a with a depth sufficient to reach or be proximate with an underground drainage trench 50 (i.e., a horizontal drain 50) designed to evacuate excess soil liquid (water) away from the subsoil. The first drainage well 60a is indicative of a drainage well depth configured for a poorly drained soil profile to quickly evacuate surface and subsurface liquid/water, thus the higher drainage well depth. Second, and still referring to FIG. 6, there is shown a second drainage well 60b with a depth sufficient to reach or be proximate with the water table 32. In such a configuration, the second drainage well 60b is again indicative of a drainage well depth of a drainage well 60 configured for a poorly drained soil profile to allow upward capillary suction from the water table 32 to the top layer 22, thus resulting in a lower depth compared to the first drainage well 60a. Other configurations of drainage well depths are contemplated in view of these considerations.

If a compacted or poorly drained soil profile is encountered about a sampling point 12, at least one of the drainage wells 60 of the drainage well network can be filled with particulate material 70 that allows for adequate capillary rise into the drainage wells 60 proximate with a water table 32, such as the second drainage well 60b, as shown in FIG. 6. In some implementations, the particulate material 70 includes a soil particulate portion (i.e., soil material) and/or an organic matter portion, as explained in further details below. It should be understood that upward suction of liquid/water by means of a particulate material 70 can play two roles. First, the particulate material 70 increases gas diffusivity by speeding the drainage of the top layer 22 and allowing bypass flow through the compacted layer 24 when subsurface drainage is required and second, it allows soil liquid (water) to irrigate an upper subsoil (e.g., redistribute bottom-up the soil liquid (water) from the drainage layer 26 to the compacted and top layers 24, 22). Thus, according to one implementation, the particulate material 70 is selected for its ability to maintain a hydraulic link between the bottom of the drainage well 60, where there may be free water, and the top layer 22, to reach the desired level of aeration. The particulate material 70 has at least two parameters: its composition and its granulometry, as explained in further details below.

According to one implementation, the composition of the particulate material 70 is a mixture characterized by unsaturated hydraulic conductivity characteristics conducive to water diffusivity and capillary rise. In another implementation, a portion of the particulate material 70 can be soil gathered about and grinded and/or sieved on-site, while another portion can be organic matter, different from soil material, such as, but not limited to, wood fibres with micropores, biochar, peat and plant seeds and cuttings, which can also be gathered and processed on-site or off-site. It is worth noting that plant seeds and cuttings added to the particulate material 70 can promote root and biopore formation, thus furthering soil aeration. According to one implementation, it was found that aggregates of a size ranging between about 0.10 mm to about 20 mm are a suitable granulometry of the particulate material 70 to enhance water redistribution and promote capillary rise in the soil. It should also be understood that the particulate material size may be modified at any point in time, as the packing, the density, the mixing process, the nature of the material composition (mineral or organic), the particle interactions and the aging process may affect the evolution of the material 70 after having been inserted into the drainage wells 60. Additional considerations may play a role in the choice of the initial granulometry of the particles.

In one implementation where a soil portion of the particulate material 70 is mixed with an organic matter portion of intermediate particle size (such as between about 0.10 mm and about 20 mm), the relative composition of the organic matter portion follows a concentration ranging between about 30 volume per volume to about 100 volume per volume. Moreover, the relative content of organic matter added to the soil portion in the particulate material filler 70 can vary depending on soil composition and can be selected to prevent clay migration, organic matter decomposition and possible clogging of the drainage wells 60. It is understood that the relative portion of soil particulate over organic matter can be determined at least in part from the type of the soil. For example, in one implementation in which a soil about the selected area 10 has a high clay content (e.g., a soil with at least about 30 volume per volume of clay content) characterized with a small particle size and low unsaturated hydraulic conductivity, a low relative content of said soil particulate can be mixed to the particulate material 70 containing organic matter or other materials so as to have adequate capillary and water redistribution action, based upon the unsaturated hydraulic conductivity curve (FIG. 10).

According to an implementation, in addition or in alternative to the particulate material 70, a soil additive mixture including at least one of a soil fertilizer (i.e., a plant nutrient) and a soil conditioner can be added to fill a vertical drainage well 60 of the drainage well network. In other words, a composition of the soil additive mixture can include additional nutrients and pH adjustments for the soil to promote plant growth when the selected area 10 is an agricultural field, for example. As such, the method 100 provided herein can influence soil properties beyond soil drainage and soil aeration considerations. As a non-limitative example in which the selected area 10 to be drained features a top layer 22 with high acidity compared to a desired pH level, as determined during the preliminary soil characterisation (101), for instance, a soil conditioner such as lime can be included in the soil additive mixture to partially fill a drainage well 60 as needed, such that the lime may gradually diffuse into surrounding soil about the drainage well 60 to increase pH levels and reduce soil acidity as desired. In the same selected area 10, soil fertilizers such as nitrogen and phosphorus can be included in the soil additive mixture, if needed. Other non-limiting examples of soil fertilizers include: potassium, sulphur, calcium, magnesium and any combination thereof. It should be noted that the means used to estimate whether the arable soil of an agricultural field requires fertilizers or conditioners for a given crop are well established in the science of agronomy. It should be noted that the soil additive mixture can be assorted with a composition of the particulate material 70 described herein according to a suitable relative content thereof.

The determined spatial distribution of the drainage wells 60 of the drainage well network pattern depends on whether the soil profile is permeable or impermeable. As mentioned, the permeability of the soil is based on the saturated hydraulic conductivity at different depths in the profile and at different locations in the selected area 10.

If the soil, in the selected area 10, has a substantially homogeneous profile, as illustrated in FIG. 5, that is highly permeable with a saturated hydraulic conductivity higher than about 1 m per day, such as a sand deposit, drainage rate models such as the steady-state Hooghoudt or Guyon formulas can be used to determine the density and/or spatial distribution of conventional horizontal drain tiles (number). Such models are well known in the field of soil science, agronomy, and hydrology, such as:

$q = R = \frac{8 K D h}{L^{2}},$

purpose of this formulae, q is the drainage rate needed from the horizontal drains 50, R is the rate of recharge per unit surface area, L is the distance between horizontal drains 50, K is the equivalent saturated hydraulic conductivity of the soil profile, h is the depth of the horizontal wells 50, and D is the equivalent drainage depth. It should be noted that in a homogeneous soil profile, the result of the generated horizontal drainage network may steer towards the installation of drainage wells 60 as indicated below.

If the soil in the selected area 10 has a homogeneous profile having a low saturated hydraulic conductivity, for instance lower than about 1 m per day in at least one of its subsoil layers above the water table 32, then another approach must be used to determine the density and/or spatial distribution of the drainage wells 60 as part of the drainage well network determination. If the soil has a substantially heterogeneous profile that is not highly permeable, that is a soil having at least one layer with saturated hydraulic conductivity lower than about 1 m per day (e.g., a compacted layer 24), the spatial distribution of drainage wells 60 is calculated to obtain a drawdown of the water table 32 of about 5 cm to about 40 cm per day, using a numerical tool known in the art, such as HYDRUS™. Alternatively, an analytical solution can be used to obtain a more approximate estimate of this density. Accordingly, the depth of the drainage wells 60 is first estimated to improve gas diffusion by setting a depth D_c(see FIG. 7) such that air-filled porosity may reach about 0.10 cm³cm⁻³to about 0.20 cm³cm⁻³by using FIG. 9 and provide a bottom-up capillary rise adequate to meet crop demand at a bottom of the top layer 22 by using the unsaturated hydraulic conductivity curve (FIG. 10). For example, setting the bottom of the drainage well at a distance D_cof about 50 cm from the bottom of the top layer 22 can improve aeration and provide adequate capillary rise. Next, a sufficient number of drainage wells (i.e. density) to receive a rainfall characteristic of an average runoff in the selected area 10 is then selected. With the distance D_cbeing determined, spatial distribution and radius of the drainage wells 60 can be determined to absorb the sudden runoff determined from weather record of about 1 cm to about 10 cm per day, for example, as mentioned hereinbefore. In view of providing an exemplary application wherein a rainfall of 3 cm over 1 hectare (ha) over a day generates a runoff of 30,000 cm³per a day, and the distance D_chas been determined to be 50 cm which, in this example, results in a drainage well depth of 80 cm from the surface 20 because the top layer 22 is 30 cm deep. Assuming that the radius of the drainage wells 60 is imposed by drilling equipment at 5 cm, then a density of 100 drainage wells can be selected to provide a volumetric capacity of 60,000 cm³per day, enough to ensure surface drainage.

Then, still to establish a density of the drainage wells 60 according to the approximative analytical approach, an approximative calculation of the table drawdown capacity is made at varying distances from the drainage wells. To expand on the previous soil profile example wherein the distance D_cis about 50 cm in the case of a homogeneous soil profile with a low hydraulic conductivity, the drawdown of the water table can be calculated from the saturated hydraulic conductivity as a function of distance and a position of the water table. In the following exemplary embodiment, and referring to FIG. 11, an analytical solution to find the a distance from the well (r) at which a desired drawdown is obtained is provided based on the formula of Dupuit for a cylindrical well in an water table in an area with a fixed potential along its boundary (in accordance with a continuity equation Q_constant=Q_w, and a boundary condition wherein at a distance R,

$h = h_{R}) : \frac{Q_{w}}{π k} (\ln \frac{R}{r}) + h_{R}^{2} = h^{2},$

wherein, for the purpose of this formulae, Q_wis a constant flow rate of the drainage well towards a permeable layer (cm³per day); k is the hydraulic conductivity (cm per day); h_ris the water table height (cm), R is the radius where h_rcan be considered stable (cm), r is the position from the center of the axis of the drainage well cylinder (cm), and h is the height of the drainage well (m).

Finally, in the continuity of the previous embodiment in which a distance r was determined, a distance d_sfrom the drainage well 60 providing a drawdown at steady-state of about 5 cm to about 30 cm per day, as desired, will be used as the mid-distance d_s/2 between two drainage wells (FIG. 8) in a systematic pattern (FIG. 2). It is understood that a more accurate estimate of distance, depth and sizes can be obtained using transient state numerical models.

To provide an exemplary application of the formula of Dupuit to determine at which distance r a desired drawdown of about 10 cm can be reached, consider the following: R=400 cm, h_R=50 cm and k=2 m per day which characterizes a compacted soil profile. Values of the drainage well flow rate Q_wcan be inputted into the formula of Dupuit until a boundary of the drainage well represented by

$(\ln \frac{R}{r})$

approaches 0 which indicates that the continuity equation is followed. In this example, the balance of the continuity equation is achieved when Q_w=−3571 cm³per day. Thereafter, the value of r can be altered until a table drawdown of 10 cm per day is reached which signifies an effect of the drainage to said distance r. As such, in this example, 10 cm per day of water table drawdown is reached at a distance r of 1 m from the drainage well if water is evacuated from the drainage well at a rate Q_wof 3571 cm³. Per the spatial distribution, a distance d_s/2 of 1 m between the drainage wells 60 is established.

According to one implementation, where the selected area 10 has a heterogeneous soil having a plurality of substantially homogeneous soil strata as represented in FIGS. 2 and 3, the spatial distribution of the drainage wells 60 can include a plurality of densities of the drainage wells 60 such that each of the density parameters is adapted for a respective one of the homogeneous soil stratum as a result of the method 100.

According to one implementation, the method 100 includes determining if a reinforcing structure, such as an elongated sleeve 64 (FIG. 7) as explained further below, should be equipped with the drainage wells 60 of the drainage well network. To this end, factors such as the general soil profile, topography and the soil type in the selected area 10 carry weight in this determination. For example, the elongated sleeve 64 may not be necessary in a stable soil profile. However, it is appreciated that an elongated sleeve 64 may prevent the collapse of soil forming the peripheral wall of the drainage wells 60 in soils with poor structure such as sandy soils, sensitive clay soils, and fine loamy soils.

If required, a remodeling of the overall soil surface 20 can be performed to promote surface drainage and prevent local water accumulation in depression, channel surface liquid/water towards the drainage wells 60 of the network and to prevent or reduce runoff during extreme rainfall events. The extent of the overall soil surface 20 remodeling can be determined using hydraulic characterization parameters and elevation readings, as detailed above.

Regarding using a result of the generated drainage well network pattern to drill and arrange a plurality of drainage wells (103), once the drainage well network has been determined (102), soil drilling can be performed according to the determined spatial distribution, diameter and depth, in some embodiments, in dry soil conditions. Drilling is performed with a mechanism that lifts the extracted soil to the surface. In some implementations, drilling can include performing a backward rotation of the wick as material may stick to the drill bit and a revolving motion will be used to remove material and render the drilling process more efficient.

According to one implementation, the holes for the drainage wells 60 of the drainage well network can be drilled manually, or using mechanical means such as a drilling machine operated by a man or a robot.

According to one implementation, and as shown in FIG. 7, an upper portion of the drilled hole has a funnel shape 62 (i.e., an inverse cone shape) to create a greater drainage area surface to funnel runoff water into the drainage wells 60 of the drainage well network pattern.

According to one implementation, the drainage wells 60 are configured to be connected to the underground drainage system, including the horizontal drains 50.

According to one implementation, the method 100 comprises equipping the drainage wells 60 of the drainage well network pattern with the elongated sleeve 64 after having drilled the plurality of holes (103), and before filling the drainage wells 60 with the particulate material filler 70 (104). The elongated sleeve 64 can have a peripheral wall made of corrugated plastic, a net material (i.e., a mesh), a paper sheath, or any other lasting material. The elongated sleeve 64 can be inserted vertically in the drilled hole(s), between the hole's peripheral wall and the filling particulate material 70, if any. The insertion of an elongated sleeve 64 can stabilize the particulate material 70 inside the drainage well hole and the peripheral wall of the drainage well 60 over longer periods of time. It will be noted that the elongated sleeve 64 can be inserted into the drainage well 60 after drilling (103) and after having the well 60 filled with filling material (104) in accordance with another implementation. It will also be noted that the elongated sleeve 64 can be inserted into the drainage well 60 immediately after drilling the hole thereof (103) but left as is for an extended period of time (e.g., several weeks) prior to having the well 60 filled with the determined particulate material 70 (104), in accordance with another implementation. Such an implementation having a delay between drilling the plurality of holes (103) and filling said holes with particulate material 104 may be appropriate if the particulate material 70 is not immediately available, for instance.

According to one implementation, and more particularly for agricultural applications, the elongated sleeve 64 is inserted and arranged at least 25 cm deep below the soil surface 20, i.e., below a plowing zone, so that farm equipment does not damage the elongated sleeve 64.

According to one implementation, the vertically-extending elongated sleeve 64 can be made of a metallic material or fitted with a metal plate or other relevant electromagnetic material to assist in locating the drainage wells 60 of the drainage well network using proximity sensors for possible re-drilling or subsequent filling and maintenance, if necessary.

Regarding filling at least some of the drainage wells 60 with a particulate material 70 of a selected granulometry (104), in some implementations, the particulate material 70 is gathered and processed about the selected area 10 (i.e., on-site). In other implementations, the composition of the particulate material 70 having been determined, the determined composition can be a mixture collected from on-site material with other selected materials.

Thus, according to one implementation, the drilled holes of the drainage wells 60 are filled with particulate material 70 gathered about the selected area 10 and grinded and/or sieved on-site, if required. It will be noted that the granulometry of the particulate material 70, including the soil particulate portion, if any, can be further controlled by grinding and/or sieving the particulate matter.

According to one implementation, the particulate material 70, such as wood, can be mixed by agricultural equipment such as a rototiller, before being pushed into the holes and falling into drainage well 60 by gravity once mixed. According to another implementation, the particulate material 70 can be gathered in a mixing tank and disposed gradually and as needed into the holes for the drainage wells 60 of the drainage well network, according to the incremental filling process described herein.

According to one implementation, a delivery means of the particulate material 70 to the drainage wells 60 includes a pre-filled log insertable into either the hole drilled for the drainage wells 60 or a cavity thereof. In one non-limiting example, the pre-filled log includes a tubular sheath having a membrane wall defining within a core comprising at least one of the determined particulate material 70 and the soil additive mixture. In one implementation, the particulate material 70 occupying the core of the pre-filled log is exclusively portioned with organic material and soil additives (i.e. without soil particulate). The membrane wall of the tubular sheath can be made of a netting such as wood fibre netting or any other natural fibre netting. Alternatively, the tubular sheath can be a rigid or a semi-rigid, for example when embodied by a metallic mesh or a cardboard tube perforated with holes. In one mode of use envisioned in the method 100, the pre-filled log is insertable into the holes drilled for the drainage well 60 of the network pattern (103). In another mode of use, the fibre log is insertable into said holes already equipped with an elongated sleeve 64 as described herein. The pre-filled log can be sized and shaped to occupy varying allotments in the hole cavity for the drainage well 60, so to leave space for additional soil particulates or additives, as needed.

According to an implementation, the particulate material 70 is substantially dry when being inserted in the drilled holes of the drainage wells 60.

According to one implementation, rooted plantlets can be driven into or about a top portion of the drainage wells 60 to promote root and biopore formation.

According to one implementation, filling the drilled holes is carried out in one step or incrementally. If the drilled holes are incrementally filled, additional filling material similar or different to the particulate material 70 present in the drainage wells 60 can be added therein to adjust and promote channeling and slow down the clogging of the drainage wells 60 in the long term.

Regardless of the elongated sleeve 64 that is selected according to one of the implementations, a subsequent verification of the degradation and state of the elongated sleeve 64 can be carried out periodically, for instance every year.

According to one implementation, the drilled holes for the drainage wells 60 of the drainage well network are filled with surface soil clods of sufficiently firm consistency to be sunk in and form good contact with the peripheral walls of the drilled hole(s) to provide stability thereto. Large soil clods fragments may complement the particulate material 70 as the clods tend to harden with time, thus improving the overall stability during the mixing process and during the operation of the drainage wells 60.

According to one exemplary implementation, the method 100 is applied to the soil profile illustrated in FIG. 7. Thus, a preliminary soil characterization (101) is carried out at different depths, namely between about 10 cm to about 20 cm, between about 20 cm and about 40 cm, and between about 60 cm to about 90 cm, or at greater depths, from which the saturated hydraulic conductivity, the retention curve, the moisture content and the gas diffusivity are measured from soil samples at two sampling points 12. Using this information, a drainage well network pattern can be generated (102).

Among the drainage well network parameters to be determined, the drainage well depth is calculated from a result of the preliminary soil characterization (101). If the retention curve of the soil is measured for a given layer at a given sampling point 12, then the suction to be maintained is determined using the maximum moisture content previously measured. More specifically, from the gas diffusivity and the corresponding moisture content, the maximum moisture content to be maintained in order to have a minimum diffusivity of 0.03 is determined. The maximum moisture content can be achieved from total porosity, having been calculated from bulk density or measured on-site, by subtracting the air content at which air-filled porosity is large enough to have a minimum gas diffusivity of 0.03. The maximum moisture content can also be obtained from the water desorption curve. Then, the water desorption curve can be used to determine which water potential (i.e., suction) should be applied to rapidly reach a volumetric liquid (water) content such that aeration is nonlimiting in the top layer 22. In the non-limiting example provided in FIG. 9, there is shown the gas diffusivity curve as a function of air-filled porosity and the equivalent suction to maintain such an air content, derived from the retention curve for a soil layer situated between 0 cm and about 25 cm of depth. Starting from the minimum gas diffusivity of 0.03 on the y-axis, the retention curve correlates a soil air-filled porosity (i.e., soil-air content) of 0.20 m³·m⁻³on the x-axis. As mentioned, FIG. 9 also shows below the x-axis equivalent values between soil air-filled porosity and negative soil water potential (suction) wherein the corresponding minimal soil water potential value is about −50 cm (or about −4.90 kPa), itself established from the water desorption curve. It should be noted that if the retention curve is not measured, then a reference curve taken from the literature can be used as an approximation of the soil in the given sampling point 12 with the drawback of not being as accurate as the retention curve stemming from empirical measurements.

Referring to the exemplary implementation illustrated with FIG. 8 having a top layer 22 featuring the retention curve shown in FIG. 9, to achieve the minimal suction of 50 cm (or about 4.90 kPa) for the top layer 22 in a given location provided by the determined spatial distribution, the drainage well 60 is to be filled with the particulate material 70. Thus, the composition and/or the granulometry of the particulate material 70 is selected so that it generates a suction of at least 50 cm in the top layer 22 to reach the desired level of aeration. Considering that the top layer 22 is generally about 25 cm deep, a water table 32 that is about 50 cm lower down can be maintained. This is achieved by drilling (103) a drainage well hole of the determined diameter of about 15 cm because of restrictions related to available drilling tools, according to one implementation, and by positioning a bottom of the drainage well 60 at least 50 cm lower therefrom, i.e., 75 cm from the surface; the sum of 50 cm and 25 cm, to ensure sufficient aeration at a soil depth of 25 cm. As a result, using a result of the generated drainage well network, two 75 cm deep holes are drilled (103).

Still referring to the exemplary implementation illustrated with FIG. 8, the soil shows a poorly drained soil with a compacted layer 24 and a perched water table 30, that is a soil having at least one layer with a saturated hydraulic conductivity of less than about 1 m per day (i.e., the compacted layer 24). In such conditions, the spatial distribution of the drainage wells 60 of the drainage well network can be determined for the selected area 10 in accordance with the method 100 to obtain a satisfactory drawdown of the perched water table 32 of about 30 to 40 cm per day. In the same example, the soil is initially saturated with water from the perched water table 32a. The drainage well diameter is still imposed at about 15 cm. The drainage wells 60 at different locations provided by the determined spatial distribution all share the same depth of 75 cm, as previously determined. The composition for the particulate material 70 for filling the drainage well holes includes a mixture of 50% soil particulates collected on-site and 50% saw dust, the mixture having known properties, such as saturated hydraulic conductivity K_s, the parameter a, and the retention curve at a given compaction level within the well. The sawdust has a granulometry between about 0.1 mm and about 50 mm. The particulate material 70 is preliminarily tested, first to confirm a maximal suction of about 9.8 kPa to about 15 kPa (i.e., about 100 cm to about 150 cm) can be exerted by the particulate material 70 before filling the drainage wells 60 therewith, and second to ensure a minimum non-saturated hydraulic conductivity K(h)_minin accordance with one of the unsaturated hydraulic conductivity formulas, such as: K(h)=K_s·e^−ah, in which K(h) is the unsaturated hydraulic conductivity, K_sis the saturated hydraulic conductivity, a is a soil-dependent constant and h is the soil water pressure head. These properties correspond to the drainage well 60 once filled and compacted. Alternatively, a water retention and unsaturated hydraulic conductivity graph such as the one seen in FIG. 10 can be selected for the density and the parameter a of the particulate material 70 and used to determine the minimum non-saturated hydraulic conductivity K(h)_min. The graph of FIG. 10 shows the fall of unsaturated hydraulic conductivity K(h) as a function of suction. As another alternative, the unsaturated hydraulic conductivity K(h) relationship with suction can be measured directly from the drainage well hole with different methods such as instantaneous profile or tension infiltrometry, see, for instance, DANE, Jacob H. et TOPP, Clarke G. (ed.). Methods of soil analysis, Part 4: Physical methods. John Wiley & Sons, 2020 or measured in a laboratory from the soil samples 40 using other methods.

The required parameters having been either measured or estimated, a series of simulations can be carried out to determine and improve the spatial distribution, using one of the models and analytical tools well known in the field of soil science, agronomy, and hydrology, such as HYDRUS™. Continuing with the exemplary implementation associated with FIG. 8 with the respective solutions described hereinbefore, the depth dimension of the drainage well(s) is selected based on adequate surface aeration and adequate capillary rise. Then, a first simulation is conducted about a sampling point 12, with four vertical drainage wells 60 (only two of which being shown in the cross-section) of a same depth, and spaced apart from each other so as to form a square with sides of a distance d_sof about 15 m. If the first simulation does not predict the satisfactory water table drawdown D_dof the initial perched water table 32a to a desired water table 32b, a second simulation can be conducted about the sampling point 12 with four drainage wells 60 now separated by a shorter distance. If, again, the second simulation does not reach the satisfactory water table drawdown D_d, the process is repeated by varying the drainage well spatial distribution until the satisfactory water table drawdown D_dof about 30 to about 40 cm per day is reached and a corresponding spatial distribution of the drainage wells 60 of the drainage well network is predicted. It should be noted that the water table 32 drawdown D_dis calculated at the point equidistant to the vertices formed by a polygon defined by the drainage wells 60 of the drainage well network. Or, as better represented in the implementation of FIG. 8 showing two out of four drainage wells 60 distanced from each other d_s, the drawdown D_dis calculated at a distance d_s/2 from one of the two drainage wells 60. Simulations can also be performed by forming a triangle between drainage wells 60, or any other shape accepted by the simulation tool.

In the previous description, non-limitative implementations of the method are described. Although these embodiments of the assembly and corresponding parts thereof consist of certain geometrical configurations as explained and illustrated herein, not all of these components and geometries are essential and thus should not be taken in their restrictive sense. It is to be understood, as also apparent to a person skilled in the art, that other suitable components and cooperation thereinbetween, as well as other suitable geometrical configurations, may be used for the method, as will be briefly explained herein and as can be easily inferred herefrom by a person skilled in the art. Moreover, it will be appreciated that positional descriptions such as “above”, “below”, “left”, “right”, “bottom”, “top”, “end” and the like should, unless otherwise indicated, be taken in the context of the figures and should not be considered limiting.

Furthermore, in the previous description, the same numerical references refer to similar elements. Furthermore, for the sake of simplicity and clarity, namely so as to not unduly burden the figures with several references numbers, not all figures contain references to all the components and features, and references to some components and features may be found in only one figure, and components and features of the present disclosure which are illustrated in other figures can be easily inferred therefrom. The implementations, geometrical configurations, materials mentioned and/or dimensions shown in the figures are optional and are given for exemplification purposes only.

In the following description, an embodiment is an example or implementation. The various appearances of “one implementation”, “an implementation” or “some implementations” do not necessarily all refer to the same implementation or embodiment. Although various features may be described in the context of a single implementation, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate implementations for clarity, it may also be implemented in a single embodiment. Reference in the specification to “some implementations”, “an implementation”, “one implementation” or “other implementations” means that a particular feature, structure, or characteristic described in connection with the implementations is included in at least some implementations, but not necessarily all implementations.

It is to be understood that the phraseology and terminology employed herein are not to be construed as limiting and are for descriptive purpose only. The principles and uses of the teachings of the present disclosure may be better understood with reference to the accompanying description, figures and examples. It is to be understood that the details set forth herein do not construe a limitation to an application of the disclosure.

Furthermore, it is to be understood that the disclosure can be carried out or practiced in various ways and that the disclosure can be implemented in embodiments other than the ones outlined in the description above. It is to be understood that the terms “including”, “comprising”, and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps or integers. If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element. It is to be understood that where the claims or specification refer to “a” or “an” element, such reference is not to be construed that there is only one of that element. It is to be understood that where the specification states that a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included.

It will be appreciated that the methods described herein may be performed in the described order, or in any suitable order.

Several alternative embodiments, implementations and examples have been described and illustrated herein. The embodiments of the invention described above are intended to be exemplary only. A person of ordinary skill in the art would appreciate the features of the individual embodiments, and the possible combinations and variations of the components. A person of ordinary skill in the art would further appreciate that any of the embodiments could be provided in any combination with the other embodiments disclosed herein. It is understood that the invention may be embodied in other specific forms without departing from the central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. Accordingly, while the specific embodiments have been illustrated and described, numerous modifications come to mind. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.

METHOD FOR DESIGNING A DRAINAGE WELL NETWORK PATTERN AND CONCEIVING SAME

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