Climate change 2014 - Synthesis Report

Remote sensing for agricultural applications: A meta-review

Understanding groundwater recharge is essential for successful management of water resources and modeling fluid and contaminant transport within the subsurface. This book provides a critical evaluation of the theory and assumptions that underlie methods for estimating rates of groundwater recharge. Detailed explanations of the methods are provided - allowing readers to apply many of the techniques themselves without needing to consult additional references. Numerous practical examples highlight benefits and limitations of each method. Approximately 900 references allow advanced practitioners to pursue additional information on any method. For the first time, theoretical and practical considerations for selecting and applying methods for estimating groundwater recharge are covered in a single volume with uniform presentation. Hydrogeologists, water-resource specialists, civil and agricultural engineers, Earth and environmental scientists and agronomists will benefit from this informative and practical book. It can serve as the primary text for a graduate-level course on groundwater recharge or as an adjunct text for courses on groundwater hydrology or hydrogeology. For the benefit of students and instructors, problem sets of varying difficulty are available at http://wwwbrr.cr.usgs.gov/projects/GW_Unsat/Recharge_Book/

/pdf/estimating-groundwater-recharge-14f47mdh8w.pdf

Estimating groundwater recharge

Field limits, tillage practices and ditch networks constitute man-made hydrological discontinuities in farmed catchments, and are expected to influence hydrological response during flood events. The purpose of this study is to assess the role of human impact, especially the existence of tillage practices and ditch network, on flood events. The study area is the farmed catchment of Roujan (0.91 km 2 ) located in Southern France for which a spatially distributed hydrological model, MHYDAS, was developed and tested. The model considers the catchment as a series of interconnected field parts linked to the ditch network. Descriptions are provided for the main model procedures: computation of Hortonian excess rainfall on fields using the Green and Ampt approach, conversion of excess rainfall to surface runoff, interaction between ditch network and groundwater using a simple Darcian model and flood routing through the ditch network using the diffusive wave model. To analyse the role of both tillage practices and the ditch network, two sets of sensitivity analysis of the model were applied. The first set studied the role of tillage practices by comparing the actual spatial distribution of tillage practices on the catchment with three hypothetical scenarios. The second set studied the role of the ditch network by comparing the actual man-made ditch network with a hypothetical drainage network automatically extracted from a digital elevation model. Results show the importance of the role of tillage and the ditch network on the form of the hydrograph, the lag time, the runoff volume and the peak discharge. This technique could also be applied to study the impact of land use change on the hydrological behaviour of the catchment.

Effects of the Spatial Organization of Agricultural Management on the Hydrological Behaviour of a Farmed Catchment During Flood Events

This contribution aims at presenting the principles that underlined the creation of the OZCAR research infras-
tructure, gathering various Critical Zone Observatories in France, and the scientific questions that drives the
observation settings.
The Critical Zone includes the fine zone between the lower atmosphere at the top of the canopy down to the
bedrock-soil interface. This lithosphere-atmosphere boundary is critical for the availability of life-sustaining
resources and critical for humanity because this is the zone where we live, where we build our cities, from which
we extract our food and our water and where we release most of our wastes. This is the fragile zone on which the
natural ecosystem relies because this is where nutrients are being released from the rocks.
OZCAR is a distributed research infrastructure gathering instrumented sites and catchments on continental
surfaces all dedicated to the observation and monitoring of the different compartments of the Critical Zone at
the national scale. All these observatories (more that 40) were all built up on specific questions (acid deposition,
flood prediction, urban hydrology. . . ), some of them more than 50 years ago, but they have all in common to
be highly instrumented, permanently funded as infrastructures. They all share the same overarching goal of
understanding and predicting the Critical Zone in a changing world. OZCAR gathers instrumented catchments,
hydrogeological sites, peatlands, glacier and permafrost regions and a spatial observatory under the common
umbrella of understanding water and biogeochemical cycles and the associated fluxes of energy by using natural
gradients and experimentation. Based on the collaboration with Southern Countries, OZCAR’s sites have a global
coverage including tropical areas and high mountainous regions in the Andes and the Himalaya.
OZCAR benefits from a French investments project called CRITEX (Innovative equipment for the critical zone,
https://www.critex.fr/critex-3/observatories/ ) that is centered on the development and deployment of innovative
instrumentation in the sites.
OZCAR was launched in 2016 under the leadership of the French Ministry in charge of Higher Education and
Research, assembling all French Research Institutions involved in environmental studies and with the ambition
of facilitating interdisciplinary research in terrestrial surfaces, stimulating instrumental development and being
visible at the international level.
The paper will presents the main common scientific questions, challenges in terms of instrumentation and
experimentation deployment, in particular in terms of co-location of sites, data base and modelling activities that
the OZCAR network plan to address in the next years.

OZCAR: the French network of Critical Zone Observatories: principlesand scientific objectives

Estimating the role of a ditch network in groundwater recharge in a Mediterranean catchment using a water balance approach

To account for the diversity of agricultural and ecosystem situations in hilly Mediterranean areas, the agro-hydrological observatory OMERE (Observatoire Mediterraneen de l’Environnement Rural et de l’Eau) monitors two farmed catchments—one in northern Tunisia and the other in southern France. Mediterranean regions are typified by a highly variable climate, with an alternation of long droughts and intense storms, and by a strong heterogeneity of soil properties, due to a combination of climate, relief, parent materials, sparse vegetation, intense land use, man-made infrastructure (ditches, terraces, etc.), and agricultural activities. In this context, OMERE aims to document the impacts of agricultural and land management on mass fluxes in Mediterranean farmed headwater catchments. The observation strategy is motivated by monitoring water, sediment, and contaminant fluxes and hydrologic and climatic variables at different spatial scales from cultivated plots and landscape elements to the catchment scale. These measurements have been performed at a fine time resolution over a long-term scale and by surveying land use, agricultural practices, and soil surface characteristics. The long-term observation strategy intends to support integrative multidisciplinary research for elucidating the conditions that improve soil and water management and delivery of ecosystem services in a Mediterranean rainfed cultivated context. The observatory has led to scientific insights regarding three scientific objectives: (i) to better understand the fluxes of water, erosion, and contaminants, especially pesticides, and of their natural and anthropogenic drivers on short- and long-term scales; (ii) to analyze the aggregate effects of farming and land management on mass fluxes across scales, from plot to catchment or landscape scales; and (iii) to derive new scenarios for sustainable agricultural management and improved delivery of ecosystem services.

https://acsess.onlinelibrary.wiley.com/doi/pdf/10.2136/vzj2018.04.0086

OMERE: A Long-Term Observatory of Soil and Water Resources, in Interaction with Agricultural and Land Management in Mediterranean Hilly Catchments

Farmed catchments in the Mediterranean area often exhibit dense networks of ditches which are also preferential zones of water table recharge, and thereby of groundwater contamination. This study presents an experimental analysis of seepage losses and related groundwater recharge patterns during a typical Mediterranean runoff event at the scale of a ditch located above a shallow water table. The objectives were (i) to evaluate the patterns of water table recharge by seepage in a ditch, (ii) to study the main flow processes occurring during recharge, and (iii) to estimate solute propagation in case of contaminated flow in the ditch.



The field observation indicated three major points. Firstly, they showed that seepage losses during a runoff event in a ditch can rapidly lead to a significant recharge of a shallow water table. Secondly, the recharge induces a groundwater mound much larger than the event plume. The infiltrated water and the accompanying solutes remained in the vicinity of the ditch. The patterns of groundwater recharge and contamination appeared very different. Lastly, both unsaturated and saturated-piston flow processes were observed which suggests that a variably-saturated flow modelling approach ought to be used to simulate the ditch-water shallow table interaction. Finally, the study indicates that the patterns of water table recharge and contamination in Mediterranean catchments with dense ditches network vary largely in space and time, and will require dense monitoring networks to estimate the evolution of the average contamination levels. Copyright © 2008 John Wiley & Sons, Ltd.

S. Negro

Papers

Estimating the role of a ditch network in groundwater recharge in a Mediterranean catchment using a water balance approach

OMERE: A Long-Term Observatory of Soil and Water Resources, in Interaction with Agricultural and Land Management in Mediterranean Hilly Catchments

An experimental study of water table recharge by seepage losses from a ditch with intermittent flow