Modeling of sediment transport in irrigation canals of Pakistan: examples of application: definition of a simple simulation tool and test on two actual canals of Pakistan: application to management strategies. Thesis

Irrigation canals / Hydraulics / Simulation models / Calibrations / Sensitivity analysis / Water management / Pakistan / Punjab / Chashma

Utilisation des incertitudes associées aux mesures altimétriques satellitaires de plan d'eau

On cherche comment utiliser les incertitudes I associées aux mesures altimétriques satellitaires de plan d'eau Y, pour quantifier l'imprécision des régressions établies entre de telles mesures et des cotes X mesurées au sol. Le but consiste à connaître les erreurs types résiduelles de régression qu'on obtiendrait si chaque valeur Yi de la série de base était remplacée par une distribution normale de moyenne Yi et d'écart type Ii. Par une méthode numérique basée sur l'utilisation de nombreux jeux de données différents, on montre les résultats suivants de portée générale, dont certains sont justifiés de façon théorique : Pour la régression exprimant Y en fonction de X : Les droites de régression sont identiques sur la série de base et la série étendue ; L'erreur type résiduelle de régression E1re sur la série étendue est fonction de l'erreur type résiduelle de régression E1rb sur la série de base et de la moyenne quadratique MQIb des incertitudes I sur la série de base : E1re = (E1rb2 + MQIb2)0.5 (0). Pour la régression exprimant X en fonction de Y : Les droites de régression calculées sur la série de base et la série étendue diffèrent. Leurs coefficients directeurs respectifs A2b et A2e sont tels que le rapport A2e/A2b, toujours inférieur ou égal à 1, décroît en fonction du rapport MQIb/ETYb, où ETYb désigne l'écart type de Y sur la série de base ; Sur la série étendue, les écarts de X par rapport à la droite de régression calée sur la série de base ont une moyenne nulle. La moyenne quadratique E3re de ces écarts est fonction de MQIb et de l'erreur type résiduelle de régression E2rb calculée sur la série de base : E3re = (E2rb2 + (A2b x MQIb)2)0.5 (Résumé d'auteur

Sediment behavior of Sangro Distributary, Mirpurkhas Sub-division, Sindh. Field report

Irrigation canals / Distributary canals / Sedimentation / Analysis / Pumps / Velocity / Pakistan / Sangro Distributary

Self-similar extinction for a diffusive Hamilton-Jacobi equation with critical absorption

International audienceThe behavior near the extinction time is identified for non-negative solutions to the diffusive Hamilton-Jacobi equation with critical gradient absorption ∂_t u − ∆_p u + |∇u|^{p−1} = 0 in (0, ∞) × R^N , and fast diffusion 2N/(N + 1) < p < 2. Given a non-negative and radially symmetric initial condition with a non-increasing profile which decays sufficiently fast as |x| → ∞, it is shown that the corresponding solution u to the above equation approaches a uniquely determined separate variable solution of the form U (t, x) = (T_e − t)^{1/(2−p)} f_* (|x|), (t, x) ∈ (0, T_e) × R^N , as t → T_e , where T_e denotes the finite extinction time of u. A cornerstone of the convergence proof is an underlying variational structure of the equation. Also, the selected profile f_* is the unique non-negative solution to a second order ordinary differential equation which decays exponentially at infinity. A complete classification of solutions to this equation is provided, thereby describing all separate variable solutions of the original equation. One important difficulty in the uniqueness proof is that no monotonicity argument seems to be available and it is overcome by the construction of an appropriate Pohozaev functional

Irrigation and energy: Issues and challenges

Water‐efficient agriculture has implied a large increase in energy consumption for irrigation in recent decades. In many irrigation systems, energy costs are now threatening their sustainability. However, new opportunities have arisen for the use of renewable energies in the irrigation sector. These are some of the aspects of the multifaceted multiple‐actor 'water–food–energy' nexus. Technical, economic and environmental issues are linked in many ways, involving farmers, water users' associations, energy suppliers, engineers and other stakeholders. The ICID session 'Irrigation and energy' triggered discussions on these multiple dimensions. This paper presents a synthesis of the presentations, discussions and conclusions. Four main questions are addressed: How do irrigation productivity and sustainability of water resources exploitation change when farmers have access to energy? What do we know about energy efficiency in irrigation systems, at farm and collective network levels? How can this efficiency be optimized by using advanced technologies, modelling tools, improved management? Is energy production an opportunity for irrigation systems? These questions have been posed based on multiple case studies from different parts of the world. The BRL network, in southern France, illustrates advanced strategies and opportunities to reduce energy consumption and develop energy production at a network level. General conclusions are drawn from this synthesis, illustrating trade‐offs and synergies that can be identified in the irrigation sector at different scales, while opportunities for future research are proposed

Flash flood mitigation as a positive consequence of anthropogenic forcing on the groundwater resource in a karst catchment

The Mediterranean coastal region is prone to high-intensity rainfall events that are frequently associated with devastating flash floods. This paper discusses the role of a karst aquifer system in the flash floods of a Mediterranean river, the Lez river. Most of the Lez river watershed is located on karst terrains where interactions between surface water and groundwater take place. During extreme rainfall events, the presence of fractures and well-developed karst features in carbonate terrains enhances the infiltration processes and involves the concentration of the recharge into highly organized and permeable flow paths. The groundwater, therefore, quickly moves towards the natural outlets of the karst system. The influence of the Lez karst aquifer system on the associated river floods dynamics is analysed while considering the spatially distributed rainfall, as well as the time series of the groundwater level within the aquifer and of the Lez river discharge measured at various gauging stations. Special attention is given to the relative importance of the surface and underground processes involved in flash flood genesis. It is shown that the karst groundwater contributes to flash floods under certain conditions, while high-rate pumping within the karst aquifer, which generates significant drawdown, may mitigate flash floods under other conditions

Surface water monitoring in small water bodies: potential and limits of multi-sensor Landsat time series

Hydrometric monitoring of small water bodies (1–10&thinsp;ha) remains rare, due to their limited size and large numbers, preventing accurate assessments of their agricultural potential or their cumulative influence in watershed hydrology. Landsat imagery has shown its potential to support mapping of small water bodies, but the influence of their limited surface areas, vegetation growth, and rapid flood dynamics on long-term surface water monitoring remains unquantified. A semi-automated method is developed here to assess and optimize the potential of multi-sensor Landsat time series to monitor surface water extent and mean water availability in these small water bodies. Extensive hydrometric field data (1999–2014) for seven small reservoirs within the Merguellil catchment in central Tunisia and SPOT imagery are used to calibrate the method and explore its limits. The Modified Normalised Difference Water Index (MNDWI) is shown out of six commonly used water detection indices to provide high overall accuracy and threshold stability during high and low floods, leading to a mean surface area error below 15&thinsp;%. Applied to 546 Landsat 5, 7, and 8 images over 1999–2014, the method reproduces surface water extent variations across small lakes with high skill (R2 = 0.9) and a mean root mean square error (RMSE) of 9300&thinsp;m2. Comparison with published global water datasets reveals a mean RMSE of 21&thinsp;800&thinsp;m2 (+134&thinsp;%) on the same lakes and highlights the value of a tailored MNDWI approach to improve hydrological monitoring in small lakes and reduce omission errors of flooded vegetation. The rise in relative errors due to the larger proportion and influence of mixed pixels restricts surface water monitoring below 3&thinsp;ha with Landsat (Normalised RMSE&thinsp; = &thinsp;27&thinsp;%). Interferences from clouds and scan line corrector failure on ETM+ after 2003 also decrease the number of operational images by 51&thinsp;%, reducing performance on lakes with rapid flood declines. Combining Landsat observations with 10&thinsp;m pansharpened Sentinel-2 imagery further reduces RMSE to 5200&thinsp;m2, displaying the increased opportunities for surface water monitoring in small water bodies after 2015.</p