Subsurface Drainage Patterns Research Articles

Study on Characteristics of Nitrogen and Phosphorus Loss under an Improved Subsurface Drainage

Agricultural drainage plays an effective role in preventing waterlogging and salinity disasters and also is the main transport pathway for agricultural non-point source pollutants into rivers and lakes. Hence, the water quality of agricultural drainage should be a point of focus. In this paper, nitrogen and phosphorus loss under improved subsurface drainage with different filter materials (gravel, layered sand-gravel, mixed sand-gravel, straw) were studied by a three-year field experiment (2016–2018) compared with the conventional subsurface drainage. The pH values, total nitrogen, ammonia nitrogen, nitrate nitrogen, total phosphorus and soluble reactive phosphate were considered. The results showed that the nitrogen and phosphorus concentrations of drain outflow under improved subsurface drainage with gravel filter were larger than that with layered sand-gravel filter and mixed sand-gravel filter. The improved subsurface drainages with layered sand-gravel filter and mixed sand-gravel filter had an effect on reducing the ammonia nitrogen, total phosphorus and soluble reactive phosphate concentrations of the outflow. Meanwhile, the characteristics of nitrogen and phosphorus loss under the improved subsurface drainage with straw filter were different from that with layered sand-gravel filter and mixed sand-gravel filter. For the improved subsurface drainage with layered sand-gravel filter outflow, the ammonia nitrogen, total phosphorus, and soluble reactive phosphate concentrations were about 13%–78%, 38%–63%, 40%–68% less, and total nitrogen, nitrate nitrogen concentrations were 24%–80%,18%–96% more than that under conventional subsurface drainage. Meanwhile, for the improved subsurface drainage with straw filter outflow, compared with conventional subsurface drainage outflow, the percentage changes of the total nitrogen, nitrate nitrogen, ammonia nitrogen, total phosphorus and the soluble reactive phosphate concentrations were about −76%–62%, −77%–78%, −152%–−274%, −103%–−400% and −221%–−291%, respectively. Additionally, in the outflow of all subsurface drainage patterns, there were much higher total nitrogen and nitrate nitrogen concentrations which should be focused on and the agricultural water management should be adopted.

HESS Opinions Catchments as meta-organisms – a new blueprint for hydrological modelling

Abstract. Catchment-scale hydrological models frequently miss essential characteristics of what determines the functioning of catchments. The most important active agent in catchments is the ecosystem. It manipulates and partitions moisture in a way that supports the essential functions of survival and productivity: infiltration of water, retention of moisture, mobilization and retention of nutrients, and drainage. Ecosystems do this in the most efficient way, establishing a continuous, ever-evolving feedback loop with the landscape and climatic drivers. In brief, hydrological systems are alive and have a strong capacity to adjust themselves to prevailing and changing environmental conditions. Although most models take Newtonian theory at heart, as best they can, what they generally miss is Darwinian theory on how an ecosystem evolves and adjusts its environment to maintain crucial hydrological functions. In addition, catchments, such as many other natural systems, do not only evolve over time, but develop features of spatial organization, including surface or sub-surface drainage patterns, as a by-product of this evolution. Models that fail to account for patterns and the associated feedbacks miss a critical element of how systems at the interface of atmosphere, biosphere and pedosphere function. In contrast to what is widely believed, relatively simple, semi-distributed conceptual models have the potential to accommodate organizational features and their temporal evolution in an efficient way, a reason for that being that because their parameters (and their evolution over time) are effective at the modelling scale, and thus integrate natural heterogeneity within the system, they may be directly inferred from observations at the same scale, reducing the need for calibration and related problems. In particular, the emergence of new and more detailed observation systems from space will lead towards a more robust understanding of spatial organization and its evolution. This will further permit the development of relatively simple time-dynamic functional relationships that can meaningfully represent spatial patterns and their evolution over time, even in poorly gauged environments.

An investigation of monitorability issues for groundwater in the Zachs Knob syncline area, Northeast Tennessee, USA

A dye trace was conducted in 2007 to verify a site conceptual model for groundwater monitorability near an orphan landfill in Sullivan County, Tennessee. The old landfill is in the Valley and Ridge physiographic province. Multiple tracing efforts in this area dating back to 1980 were either unsuccessful or yielded ambiguous results, causing the site to be deemed un-monitorable. Available geologic information, water chemistry data, and subsurface investigation results were compiled to produce a site conceptual model for about 120 ha of land, including the old landfill area. Eosine dye was used as a mimic for potential contamination effects in order to document the monitorability of the local aquifer as part of a hydrogeologic report for a new disposal facility permit. The site exhibits characteristics of a youthful karst setting at the surface. Overflow conduits left behind from a geologically older hydrologic system were found after detailed investigation. These remnant karst features were adjusted to a higher baseflow regime and act as a constraint to the maximum water table elevations in the present hydrologic system. Eosine dye was chosen as the best surrogate leachate after background water and bench scale leachate/dye interaction tests were done. The eosine injection was conducted in a variety of ways across the site to mimic potential leachate release scenarios from the proposed liner system for a new solid waste disposal facility. Eosine was visually detected in local springs and positively detected in some domestic supply and monitoring wells. Subsurface drainage patterns indicated two main groundwater basins in the area of study. Follow-up dye traces with simultaneous injections of pyranine and sulforhodamine B were conducted in 2009 to comply with the request of State regulators. The inferred drainage patterns were confirmed with dye detections at proposed monitoring points for each of the two main groundwater basins.

Soil and landscape attributes interpret subsurface drainage clusters

Water in excess of evapotranspiration follows topographically defined flow paths and can affect spatial subsurface drainage patterns. This 1993–2003 field study was conducted near Nashua, Iowa, to delineate the subsurface drainage clusters and identify the landscape and hydrologic variables that contributed significantly in discriminating these clusters. A digital elevation model was developed using 6695 elevation data measurements collected with GPS navigation system across 36 field plots (0.4 ha in size each). A spherical model was used to interpolate the elevation data within a Spatial Analyst tool of ArcGIS software. Plot-scale average topographic attributes of elevation, slope, aspect, and curvature were derived using the Zonal function in the Spatial Analyst tool. Hydrologic attributes of flow direction, flow length, and flow accumulation were derived using the Hydrology module of Spatial Analyst tool after performing Fill function for the sink areas. Annual normalised subsurface drainage data and plot-scale derived soil and topographic attributes were used in the cluster and discriminant analysis, respectively, to investigate their relationships. Stepwise discriminant analysis identified elevation and flow accumulation as the variables that discriminated the subsurface drainage clusters of low, medium, and high categories significantly (P = 0.01). The role of elevation and flow accumulation was verified using discriminant functions that predicted all members of the high drainage cluster accurately with zero error rates. GIS data layer of subsurface drainage clusters also showed that high drainage clusters were located at the lower elevation levels and were in close agreement with the elevation and flow accumulation data layers. The results of this study indicate that elevation and flow accumulation GIS data layers can be used as a guideline to minimise nutrient losses through subsurface drainage water.

USING DISCRIMINANT ANALYSIS AND GIS TO DELINEATE SUBSURFACE DRAINAGE PATTERNS

The contamination of soil and water resources from nutrients, transported in subsurface drainage water havingdifferent drainage patterns, has important repercussions on the ecological environment and human health. This study wasdesigned to delineate subsurface drainage patterns using cluster analysis based on six years (1993 to 1998) of field measureddata on subsurface drainage flows from thirty-six 0.4 ha field experimental plots. These drainage patterns then were relatedspatially to the soil and topographic attributes using discriminant analysis and the map overlay capability of GeographicInformation Systems (GIS) to develop cause-effect relationships. The experimental field plots, under various tillage and nitrogenmanagement treatments, were located on glacial till derived soils at Iowa State Universitys Northeastern Research Centernear Nashua, Iowa. The field-measured subsurface drainage volumes were normalized to make comparisons over all plotsand years, and the normalized data were used in the subsequent statistical and GIS analyses. After performing cluster analysis,the output was generated as GIS data layers showing low, medium, and high drainage areas. Stepwise discriminant analysisidentified elevation, slope, and average normalized yield as the factors contributing significantly (P < 0.10) to theformation of subsurface drainage zones. GIS data layers of the factors, identified during discriminant analysis, were overlaidon the drainage patterns to study the spatial relationships. Map overlay analysis showed that high drainage areas were consistentlyfound at low elevation levels in the vicinity of Floyd soils over the 6-year study period. The combined use of discriminantanalysis and GIS was found to be effective in delineating subsurface drainage zones so that appropriate managementpractices can be applied to mitigate the environmental effects resulting from medium and higher subsurface drainage effluents.

Guidelines to prevention of slope failure related disasters in granitic bedrock areas of Malaysia

A variety of slope failures have occurred in the granitic bedrock areas of Malaysia; the more important of which are slump and debris flows that have sometimes led to considerable economic loss and loss of life. These failures have occurred at cut and fill slopes, as well as at natural ground slopes, having a varied vegetation cover ranging from primary and secondary forest to agricultural crops and grass. The failures have mainly involved weathered materials from morphological Zones I and II of the weathering profiles (or rock mass weathering grades 3 to 6) over granitic bedrock. Several factors are responsible for the failures, though the main cause is saturation and loss of negative pore water pressures within slope materials as the failures have mostly occurred during, or following, short periods «3 he) of intense rainfall (when total rainfall >70 mm), or longer periods (>1 day) of continuous rainfall. In order to prevent slope failure related disasters, it is necessary to evaluate the various factors that give rise to the failures. The regional and local topographic settings of any site or area proposed for development needs to be first evaluated in order to allow recognition of the earth materials present and the earthworks that may be necessary. Evaluation of the local topographic setting is particularly important as the location of buildings and other structures needs to be considered with reference to the surrounding terrain. Surface and subsurface drainage patterns at the proposed site and surrounding area should then be evaluated as they influence variations in moisture contents and pore water pressures within slope materials. Stream channels and valleys also directly control the movement of debris flows in hilly to mountainous terrain. The rainfall at the proposed site and surrounding area also needs to be monitored in order to allow recognition of significant rainfall intensities and/or durations that increase the likelihood of slope failures. The vegetation cover at the proposed site and surrounding area also needs to be monitored as changes in this cover can also give rise to variations in moisture contents and pore water pressures within slope materials. The stability of cut and fill slopes associated with earthworks at the proposed site or area should finally be evaluated. Consideration and evaluation of all these factors will serve as guidelines that can prevent slope failure related disasters in the granitic bedrock areas of Malaysia.

Phragmites australis invasion and expansion in tidal wetlands: Interactions among salinity, sulfide, and hydrology

Through their physiological effects on ion, oxygen, and carbon balance, respectively, salinity, sulfide, and prolonged flooding combine to constrain the invasion and spread ofPhragmites in tidal wetlands. Initial sites of vigorous invasion by seed germination and growth from rhizome fragments appear limited to sections of marsh where salinity is <10‰, sulfide concentrations are less than 0.1 mM, and flooding frequency is less than 10%. In polyhaline tidal wetlands the invasion sites include the upland fringe and some high marsh creek banks. The zones of potential invasion tend to be larger in marshes occupying lower-salinity portions of estuaries and in marshes that have been altered hydrologically. Owing to clonal integration and a positive feedback loop of growth-induced modification of edaphic soil conditions, however, a greater total area of wetland is susceptible toPhragmites expansion away from sites of establishment. Mature clones have been reported growing in different marshes with salinity up to 45‰, sulfide concentration up to 1.75 mM, and flooding frequency up to 100%. ForPhragmites establishment and expansion in tidal marshes, windows of opportunity open with microtopographic enhancement of subsurface drainage patterns, marsh-wide depression of flooding and salinity regimes, and variation in sea level driven by global warming and lunar nodal cycles. To avoidPhragmites monocultures, tidal wetland creation, restoration, and management must be considered within the context of these different scales of plant-environment interaction.

A numerical approach to subsidence prediction and stress analysis in coal mining using a laminated model

Subsidence due to underground mining may cause damage to surface structures and farmland and change surface and subsurface drainage patterns. During the past few decades, a number of subsidence prediction techniques have been proposed. Currently, the influence function method is the most widely used method for prediction of longwall coal mining subsidence. The influence function method may provide accurate results if a suitable function can be established for a specific site or region based on field observations. The method, however, suffers from generality, and cannot be used in virgin areas. Furthermore, there is a need to develop a model which can simultaneously analyze in-mine stability of mine workings including roof-pillar-floor interaction and associated surface and subsurface subsidence. Since the rock mass surrounding coal seams usually consists of distinct layers/beds and field observations suggest relative movements along bed interfaces, a homogeneous isotropie continuum model cannot effectively describe ground movements due to coal mining. Therefore, in finite element modeling some investigators reduce the values of the Young's modulus to very small, say one percent of the original laboratory value, to obtain acceptable subsidence results, e.g. Bowders et al [1]. Valuable attempts have also been made to model the sliding between beds in finite element modeling [2], but results have been presented only for two-dimensional problems due to large memory and computation time requirements for three-dimensional problems. A three-dimensional numerical model based on a laminated medium used in conjunction with boundary element technique was developed to simulate the ground movements due to coal mining, and results obtained were reasonable [3]. Recently, this model has been further modified to simultaneously analyze both subsidence and in-mine stability of mine workings including roof-pillar-