subsurface flow
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Author(s):  
Mariana Jimenez ◽  
Nicolás Velásquez ◽  
Jhon Esteban Jimenez ◽  
Janet Barco ◽  
Daniela Blessent ◽  
...  

2021 ◽  
Author(s):  
Catherine Spurin ◽  
Gaetano Garfi ◽  
Maja Rücker ◽  
Tom Bultreys ◽  
Samuel Krevor ◽  
...  

Understanding the interaction between competing fluids in the pore space of rocks is key for predicting subsurface flow and trapping, such as with CO2 in a saline aquifer. These processes occur over a large span of timescales (from seconds to thousands of years), and length scales (from microns to kilometres). Understanding the link between these temporal and spatial scales will enable us to interpolate between observations made at different resolutions. In this work we explore the temporal scales present during macroscopically steady-state multiphase flow in a porous rock using differential pressure measurements. We observe a cascade of timescales in the pressure differential i.e. a continuous range of frequencies, with lower frequencies having greater amplitudes. We demonstrate a scaling of the spectral density with frequency of S ∼ 1/f^2, or red noise, to describe the dynamics. This scaling is independent of the flow rate of the fluids or the fraction of the flow taken by water. This red, or Brownian, noise indicates a stochastic process where pressure fluctuations are seen throughout the pore space, resulting in intermittent filling of pores over a wide range of time-scales, from seconds to minutes in these experiments. This observation will aid future modelling of subsurface flow as it suggests self-organised critically of the system with no characteristic time or length scale.


2021 ◽  
Vol 9 ◽  
Author(s):  
Feleke K. Sishu ◽  
Ayele M. Bekele ◽  
Petra Schmitter ◽  
Seifu A. Tilahun ◽  
Tammo S. Steenhuis

Establishing worldwide sustainable and phosphorus efficient cropping systems is urgently needed because the supply of suitable phosphate rock is limited, and excess phosphorus in streams causes eutrophication. One of the impediments in the developing world for sustainable P practices is the lack of studies on P transport and its eventual disposition in the environment. One of these regions with few studies is the Ethiopian Highlands, with permeable volcanic soils. The objective was to establish baseline data on P watershed export in the (sub)humid highlands. Two contrasting watersheds were selected near Lake Tana. For 2 years, stream discharge and sediment, total P, dissolved P, and bioavailable particulate P concentrations were determined at the watershed outlet. The first watershed is the 57 km2 Dangishta, with lava intrusion dikes, forcing subsurface flow through faults to the surface and preventing gully formation. Subsurface flow was half of the 1745 mm annual precipitation, and surface runoff and erosion were minimal. The second watershed is the 9 km2 Robit Bata with 1,420 mm precipitation. The banks of several river banks were slumping. The upper part of the watershed generates saturation excess runoff. A hillslope aquifer in the lower part provided interflow. The average sediment concentrations of 10.5 g L−1 in the stream in Robit Bata (11 times that in Dangishta) reflected the sediments from banks slipping in the stream. The hydrology and the soil loss directly affected the phosphorus export. In Dangishta, the total P concentration averaged 0.5 mg L−1 at the outlet. In Robit Bata, the average total P concentration was 2 mg L−1. The bioavailable particulate P concentration was only twice the concentration in the runoff water. The low phosphorus content of the subsoil slipping in Robit Bata moderated biologically available particulate P at the outlet. Average dissolved P concentrations for both watersheds were around 0.1 mg L−1 in the low range found in temperate climates. It reflects the difference in length of time that phosphorus fertilizers have been applied. Our research concludes that commonly implemented practices such as strengthening river banks and stabilizing gully might not lead to improved water quality in Lake Tana.


2021 ◽  
Author(s):  
Tetsu K Tokunaga ◽  
Jiamin Wan ◽  
Phuong Anh Tran ◽  
Wenming Dong ◽  
Alexander Newman ◽  
...  

Author(s):  
Mario Pirastru ◽  
Massimo Iovino ◽  
Hassan Awada ◽  
Roberto Marrosu ◽  
Simone Di Prima ◽  
...  

Lateral saturated soil hydraulic conductivity, Ks,l, is the soil property governing subsurface water transfer in hillslopes, and the key parameter in many numerical models simulating hydrological processes both at the hillslope and catchment scales. Likewise, the hydrological connectivity of lateral flow paths plays a significant role in determining the intensity of the subsurface flow at various spatial scales. The objective of the study is to investigate the relationship between Ks,l and hydraulic connectivity at the hillslope spatial scale. Ks,l was determined by the subsurface flow rates intercepted by drains, and by water table depths observed in a well network. Hydraulic connectivity of the lateral flow paths was evaluated by the synchronicity among piezometric peaks, and between the latter and the peaks of drained flow. Soil moisture and precipitation data were used to investigate the influence of the transient hydrological soil condition on connectivity and Ks,l. It was found that the higher was the synchronicity of the water table response between wells, the lower was the time lag between the peaks of water levels and those of the drained subsurface flow. Moreover, the most synchronic water table rises determined the highest drainage rates. The relationships between Ks,l and water table depths were highly non-linear, with a sharp increase of the values for water table levels close to the soil surface. Estimated Ks,l values for the full saturated soil were in the order of thousands of mm h-1, suggesting the activation of macropores in the root zone. The Ks,l values determined at the peak of the drainage events were correlated with the indicators of synchronicity. The sum of the antecedent soil moisture and of the precipitation was correlated with the indicators of connectivity and with Ks,l. We suggest that, for simulating realistic processes at the hillslope scale, the hydraulic connectivity could be implicitly considered in hydrological modelling through an evaluation of Ks,l at the same spatial scale.


Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2200
Author(s):  
Georgios D. Gikas ◽  
Vassiliki A. Papaevangelou ◽  
Vassilios A. Tsihrintzis ◽  
Maria Antonopoulou ◽  
Ioannis K. Konstantinou

We assessed constructed wetland (CW) performance in the removal of six emerging pollutants (EPs) from university campus wastewater. The EPs considered were: diethyl phthalate (DEP), di-isobutyl phthalate (DIBP), di-n-octyl phthalate (DNOP), bis(2-ehtylxexyl) phthalate (DEHP), tris(1-chloro-2-propyl) phosphate (TCPP) and caffeine (CAF). Six pilot-scale CWs, i.e., three horizontal subsurface flow (HSF) and three vertical flow (VF), with different design configurations were used: two types of plants and one unplanted for both the HSF and the VF, two hydraulic retention times (HRT) for the HSF, and two wastewater feeding strategies for the VF units. The results showed that the median removals in the three HSF-CWs ranged between 84.3 and 99.9%, 79.0 and 95.7%, 91.4 and 99.7%, 72.2 and 81.0%, 99.1 and 99.6%, and 99.3 and 99.6% for DEP, DIBP, DNOP, DEHP, TCPP, and CAF, respectively. In the three VF-CWs, the median removal efficiencies range was 98.6–99.4%, 63.6–98.0%, 96.6–97.8%, 73.6–94.5%, 99.3–99.5% and 94.4–96.3% for DEP, DIBP, DNOP, DEHP, TCPP and CAF, respectively. The study indicates that biodegradation and adsorption onto substrate were the most prevalent removal routes of the target EPs in CWs.


2021 ◽  
Vol 25 (12) ◽  
pp. 6185-6202
Author(s):  
Ather Abbas ◽  
Sangsoo Baek ◽  
Norbert Silvera ◽  
Bounsamay Soulileuth ◽  
Yakov Pachepsky ◽  
...  

Abstract. Contamination of surface waters with microbiological pollutants is a major concern to public health. Although long-term and high-frequency Escherichia coli (E. coli) monitoring can help prevent diseases from fecal pathogenic microorganisms, such monitoring is time-consuming and expensive. Process-driven models are an alternative means for estimating concentrations of fecal pathogens. However, process-based modeling still has limitations in improving the model accuracy because of the complexity of relationships among hydrological and environmental variables. With the rise of data availability and computation power, the use of data-driven models is increasing. In this study, we simulated fate and transport of E. coli in a 0.6 km2 tropical headwater catchment located in the Lao People's Democratic Republic (Lao PDR) using a deep-learning model and a process-based model. The deep learning model was built using the long short-term memory (LSTM) methodology, whereas the process-based model was constructed using the Hydrological Simulation Program–FORTRAN (HSPF). First, we calibrated both models for surface as well as for subsurface flow. Then, we simulated the E. coli transport with 6 min time steps with both the HSPF and LSTM models. The LSTM provided accurate results for surface and subsurface flow with 0.51 and 0.64 of the Nash–Sutcliffe efficiency (NSE) values, respectively. In contrast, the NSE values yielded by the HSPF were −0.7 and 0.59 for surface and subsurface flow. The simulated E. coli concentrations from LSTM provided the NSE of 0.35, whereas the HSPF gave an unacceptable performance with an NSE value of −3.01 due to the limitations of HSPF in capturing the dynamics of E. coli with land-use change. The simulated E. coli concentration showed the rise and drop patterns corresponding to annual changes in land use. This study showcases the application of deep-learning-based models as an efficient alternative to process-based models for E. coli fate and transport simulation at the catchment scale.


2021 ◽  
Vol 19 (1) ◽  
pp. 101-111
Author(s):  
A.A. BADEJO ◽  
J. M. NDAMBUKI ◽  
W. K. KUPOLATI ◽  
S. ADEYEMO ◽  
D. O. OMOLE ◽  
...  

Abattoir wastewater is high in organic content, the waste recovery and treatment facility is expensive and this results in indiscriminate dumping into streams without adequate treatment. The effectiveness of using a two-stage subsurface flow constructed wetland to treat abattoir effluent was examined in this study. Diluted abattoir wastewater from Lafenwa Abattoir, Abeokuta, Ogun State, Nigeria was fed into a two-stage Vegetated Subsurface Bed Constructed Wetlands (VSBCW). The VSBCW consisted of 500 mm deep 10-15 mm diameter granite with 150 mm thick overlay of well graded sand planted with locally available Vetiveria nigritana. Grab samples were collected at selected points along Ogun river and measurement of physico-chemical parameters such as: Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD5), Electrical Conductivity (EC), Total Dissolved Solids (TDS) and Total Suspended Solid (TSS) of the influent and effluent from the VSBCW were carried out. Irrigation with water and diluted abattoir wastewater to examine the variation in plant growth rate was also investigated. The results revealed a pollution load reduction as the wastewater moves away from the discharge point but inadequate to meet the FEPA (1991) standard for wastewater discharge into rivers. The VSBCW was observed to reduce the concentration of BOD5, COD, EC, TDS and TSS in the abattoir wastewater by 88.71, 87.28, 45.72, 56.89 and 72.27 % respectively. The growth rate of the V. nigritana reduced by 1.9% when irrigated with abattoir wastewater. The study revealed that locally available V. nigritana in VSBCW is effective in abattoir wastewater treatment and could be use to curtail the pollution caused by discharge of untreated wastewater into rivers.      


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