The potential of fragipans in sustaining pearl millet during drought periods in north-central Namibia

Sandy soils with fragipans are usually considered poorly suited for agriculture. However, these soils are cultivated in Namibia as they can secure a minimum harvest during droughts. In order to understand the hydrological influence of fragipans in these soils, Ehenge, their soil moisture content was measured for 4 months. These data were then compared to a deep soil without fragipan, Omutunda, which is more productive during normal years but less productive during droughts. The results illustrate that the combination of sandy topsoil and shallow fragipan has beneficial effects on plant-available water during dry periods. Three reasons can be determined: (i) high infiltration rate in the sandy topsoil, (ii) prevention of deep drainage by the fragipan, and (iii) limitation of evaporation losses through the sand. Consequently, transferring these findings to other dry, sandy areas with fragipans, with respective consequences on farming practices, crop productivity, and food security, should be possible.

Topography Impacts Hydrology in the Sub-Humid Ethiopian Highlands

Understanding the relationship between topography, hydrological processes, and runoff source areas is essential in engineering design, such as predicting floods and implementing effective watershed management practices. This relationship is not well defined in the highlands with a monsoon climate and needs further study. The objective of this study is to relate topographic position and hydrological response in tropical highlands. The research was conducted in the Debre Mawi watershed in the northwest sub-humid Ethiopian highlands. In the monsoon rain phase of 2017 and 2018, groundwater depth, infiltration rate, and surface runoff were monitored at the upslope, midslope, and downslope positions. Surface runoff rates were measured in farmer fields through distributed V-notch weirs as estimates of positional runoff. Average water table depths were 30 cm deep in the downslope regions and 95 cm in the upslope position. The water table depth affected the steady-state infiltration rate in the rain phase. It was high upslope (350 mm h−1), low midslope (49 mm h−1), and zero downslope. In 2017, the average runoff coefficients were 0.29 for the upslope and midslope and 0.73 downslope. Thus, topographic position affects all aspects of the watershed hydrology in the humid highlands and is critical in determining runoff response.

The Radius of Influence Myth

Empirical formulas to estimate the radius of influence, such as the Sichardt formula, occasionally appear in studies assessing the environmental impact of groundwater extractions. As they are inconsistent with fundamental hydrogeological principles, the term “radius of influence myth” is used by analogy with the water budget myth. Alternative formulations based on the well-known de Glee and Theis equations are presented, and the contested formula that estimates the radius of influence by balancing pumping and infiltration rate is derived from an asymptotic solution of an analytical model developed by Ernst in 1971. The transient state solution of this model is developed applying the Laplace transform, and it is verified against the finite-difference solution. Examining drawdown and total storage change reveals the relations between the presented one-dimensional radial flow solutions. The assumptions underlying these solutions are discussed in detail to show their limitations and to refute misunderstandings about their applicability. The discussed analytical models and the formulas derived from it to estimate the radius of influence cannot be regarded as substitutes for advanced modeling, although they offer valuable insights on relevant parameter combinations.

Potential Impacts of Climate Change on Land Degradation and Desertification

Land degradation and desertification have been graded as a major environmental and social dispute in most of the emerging countries. Changes in temperature, wind speed, and precipitation patterns will influence plant biomass production, land use, land cover, soil moisture, infiltration rate, runoff and crop management, and ultimately, land degradation. Close relations between climate change and land degradation processes have been perceived in the past decades. Climate change models and land use models should be combined with hydrologic/erosion models to accurately compute or predict climate change impacts on land degradation. This chapter introduces the advancements in modeling of impact of climate changes in land degradation and need for the critical investigation to better understand and forecast the responses of land degradation processes to a changing climate in the future.

Site selection for managed aquifer recharge in the city of Kabul, Afghanistan, using a multi-criteria decision analysis and geographic information system

While the success and sustainability of managed aquifer recharge (MAR) strongly depends on many characteristics of the site, it is necessary to integrate the site characteristics and develop suitability maps to indicate the most suitable locations. The objective of this study is to integrate geographic information system (GIS) and multi-criteria decision analysis (MCDA) techniques to identify the most suitable areas for a MAR project in the Kabul city area, Afghanistan. Data for six effective criteria, including slope, drainage density, surface infiltration rate, unsaturated zone thickness, soil type and electrical conductivity, were collected and then a classification map was produced for each criterion in the GIS environment. By applying MCDA techniques, the weights of the effective criteria were obtained. A suitability map was generated from each technique separately based on a combination of all criteria weights and thematic layers. The result of the analytical network process (ANP) method was found to be more precise and reliable compared with that of the analytical hierarchy process (AHP) method. Based on the final suitability map produced from the ANP model, there is 3.7, 15.0, 37.4, 33.1 and 10.3% of the total area that is unsuitable, of low suitability, moderately suitable, suitable and very suitable for MAR application, respectively. As a final result of this work, seven sites have been prioritized based on land use. The integration of multi-criteria decision analysis and GIS is recognized as an effective method for the selection of managed aquifer recharge sites.

CARACTERIZAÇÃO FÍSICO-HÍDRICA DO SOLO APÓS CULTIVOS FERTIRRIGADOS COM ÁGUA RESIDUÁRIA TRATADA

CARACTERIZAÇÃO FÍSICO-HÍDRICA DO SOLO APÓS CULTIVOS FERTIRRIGADOS COM ÁGUA RESIDUÁRIA TRATADA* FERNANDO LOPES GODINHO1; EDSON FAGNE DOS SANTOS2; SILVANIO RODRIGUES DOS SANTOS1, MARCOS KOITI KONDO1; MARFFÍSIA AMARAL RODRIGUES FERREIRA1 1Departamento de Ciências Agrárias, Universidade Estadual de Montes Claros, Rua Reinaldo Viana, 2630, Bico da Pedra, 39440-000, Janaúba, MG, Brasil, [email protected]; [email protected]; [email protected] 2Departamento de Agronomia, Universidade Federal de Viçosa, Avenida P.H Rolfs, S/N. CEP: 36570-900, Viçosa – MG, Brasil, email: [email protected] *Artigo proveniente da dissertação de mestrado do primeiro autor. 1 RESUMO Elevadas cargas de esgoto são destinadas aos corpos d'água no Brasil, podendo essa realidade ser mudada com o emprego de tecnologias para o uso agrícola desse resíduo. Assim, objetivou-se quantificar as mudanças no movimento e retenção de água em Latossolo Vermelho Eutrófico, após cultivo sequencial com a aplicação de água residuária sanitária tratada (ART). Para isso, foram utilizados cinco tratamentos (0= água limpa e adubação mineral; 50%; 100%; 150% e 200% da dose de ART limitada pelo elemento referência K+ nos 3 primeiros cultivos e; 0= água limpa e adubação mineral; 100%; 200%; 300% e 400% da dose de ART limitada pelo elemento referência Na+ no abacaxizeiro), no delineamento em blocos casualizados, com quatro repetições. Observou-se uma diminuição linear de 0,0972 mm h-1, 0,0997 mm h-1 e 0,0073 cm h-1 na taxa de infiltração básica, no tempo de 1,5 h e na condutividade hidráulica, respectivamente, para cada mm de efluente adicionado no solo, além de aumentar a porcentagem de sódio trocável nas profundidades avaliadas. No entanto, tais alterações não ultrapassam os limites considerados seguros pela literatura. Palavras-chave: infiltração; retenção de água; fertirrigação; esgoto sanitário. GODINHO, F. L.; SANTOS, E. F.; SANTOS, S. R.; KONDO, M. K.; FERREIRA, M. A. R. PHYSICAL-HYDRICAL CHARACTERIZATION OF THE SOIL AFTER FERTIRRIGATED CROPS WITH TREATED SANITARY WATER 2 ABSTRACT High sewage loads are still released into water sources in Brazil. This can be changed using technologies that contributes for the use of part of this wastewater in agriculture. This study aimed to evaluate possible changes in the movement and water retention in Eutrophic Red Latosol, after sequential cultivation with the application of treated sanitary wastewater (ART). Five treatments were used (0: clean water and mineral fertilization, 50%, 100%, 150% and 200% of the ART dose limited by the reference element K+ in the first 3 cultivation and 0: clean water and mineral fertilization, 100%, 200%, 300% and 400% of the ART dose, limited by the reference element Na+ in pineapple crops, in a randomized block design with four replications. A linear decrease of 0.0972 mm h-1, 0.0997 mm h-1 and 0.0073 cm h-1, respectively, was observed in the basic infiltration rate, in the time of 1.5 h, and hydraulic conductivity, for each mm effluent increased in the soil; in addition, in the percentage of exchangeable sodium at depths evaluated. However, such changes do not exceed the limits considered safe by the literature. Keywords: infiltration; water retention; fertigation; sanitary sewage; water reuse.

Contribution of Soil Physical Propreties in The Assessment of Flood Risks in Tropical Areas. Case of The Mbo Plain

Flooding occurs when water is in excess and can no longer be evacuated normally. The nature of the soil has been identified as one of the major causes of flooding, hence this study aimed is to show the influence of the physico-chemical properties of the soil on the recurrence of flooding in the Mbo plain. Four soil profiles were carried out on the alluviums according to the altitudes. These profiles were described and undisturbed soil samples were taken. Then, measurements of the infiltration rate of water in the soil by the Porchet method were carried out in sixteen sites. Finally, soil samples taken by auger and core sampling were studied in the laboratory. Physico-chemical parameters such as grain size, porosity, moisture, pH, compactness and organic matter were determined. Infiltration tests carried out in situ using the Porchet method revealed a hydraulic conductivity between 10−5 and 10−7 m/s, characteristic of a semi-permeable soil. This low value of permeability results from the morpho-structural arrangement and the chemical composition of the soils of the plain. These soils are hydromorphic, which means that they are constantly flooded and temporarily waterlogged. They are more or less sandy-clay on the surface, and very clayey at depth, generally from 25 cm. The very clayey soils at the base considerably slow down infiltration and act as a real barrier layer that prevents water from infiltrating, resulting to intense runoff. These soils are very porous and compact with a fairly high water content of up to 71%. This work allows us to conclude on the role of intrinsic soil properties on the genesis of floods in lowland areas. As in many plains in Africa and in the world, the nature of the soil in the Mbo plain is a natural predisposing factor to flood risks. The methods used can be applied in areas with the same characteristics as the Mbo Plain.

An expert system for predicting the infiltration characteristics

Infiltration plays a fundamental role in streamflow, groundwater recharge, subsurface flow, and surface and subsurface water quality and quantity. This study includes a comparative analysis of the two machine learning techniques; M5P model tree (M5P) and Gene Expression Programming (GEP) in predictions of the infiltration characteristics. The models were trained and tested using the 7 combination (CMB1 – CMB7) of input parameters; moisture content (m), bulk density of soil (D), percentage of the silt (SI), sand (SA) & Clay (C), and time (t), with output parameters; cumulative infiltration (CI) and infiltration rate (IR). Results suggested that GEP has an edge over M5P to predict the IR and CI with R, RMSE & MAE values 0.9343, 15.9667 mm/hr & 8.7676 mm/hr, and 0.9586, 9.2522 mm and 7.7865 mm for IR and CI, respectively with CMB1. Although the M5P model also gave good results with R, RMSE & MAE values 0.9192, 14.1821 mm/hr, & 19.2497 mm/hr, and 0.8987, 11.2144 mm & 18.4328 mm for IR and CI, respectively, but lower than GEP. Furthermore, single-factor ANOVA and uncertainty analysis were used to show the significance of the predicted results and to find the most efficient soft computing techniques respectively.

Retention Pool As Alternative For Flood Control Case Study Of Bapertarum Housing, Sumenep Regency

Indonesia is a water country with thousands of rivers and hundreds of deep seas. This causes Indonesia to become a country that is very prone to flooding. But basically, there are several factors that cause this to happen, namely: natural events, drainage damage and environmental degradation caused by human activity itself. Geographically, Bapetarum Housing is an area located in a rainwater catchment area so that it is prone to flood events. High rainfall intensity can cause flood inundation as high as 30 cm. The purpose of this study is to calculate the adequacy of the retention pond to cope with flooding. The procedure for collecting research data begins with analyzing the flood, namely primary and secondary data. Meanwhile, the data analysis techniques used are planning rain analysis, rainfall intensity, flood discharge analysis, retention pond capacity. The retention pond capacity is sufficient because the dimensions of the retention pond are larger than the volume of the retention pond capacity when the flood is 6750m3>6447m3. The retention pond is planned in the downstream area of the residential river with a pool area of 50 x 40 meters and a depth of 4.5 m. The bottom condition of the pond is saturated because it is always inundated with water, the infiltration rate is constant (fc). The constant infiltration for clayey soil type is 0.5 m/day, the infiltration volume rate that occurs at the bottom of the pond is 179 m3/hour, the volume is below the threshold 8283.21 m3, infiltration time is 46 hours.

Effects of grass type on hydraulic response of the three-layer landfill cover system

Soil column tests were conducted to investigate the effects of grass type on water infiltration in a three-layer landfill cover under drying and wetting conditions. Five soil columns were prepared, including one bare, two Bermuda grass-planted and the other two vetiver-planted. During the drying period, the suction of vetiver-planted soil column was the largest, while that of bare case was the lowest. During the wetting period, the infiltration rate shows a bimodal form due to the contrasting hydraulic properties of different soil layers. The infiltration rate of vetiver-planted soil column was the lowest, followed by Bermuda grass-planted and bare cases. Correspondingly, the vetiver-planted soil column retained the maximum suction and the deepest ponding depth during rainfall. This was likely due to the larger leaf area and deeper roots of vetiver than those of Bermuda grass, thus inducing the maximum initial suction by root water uptake before rainfall and reducing the water permeability by root occupations of soil pores. These results show that vetiver is more effective than Bermuda grass to reduce water percolation through the three-layer landfill cover.