Hocine Bendjoudi

DISCUSSION of "Evidence of chaos in the rainfall-runoff process" Which chaos in the rainfall-runoff process?

Abstract In the 1980s, there were numerous claims, based on estimates of the correlation dimension, that the variability of various geophysical processes, in particular rainfall, is generated by a low-dimensional deterministic chaos. Due to a recent attempt (Sivakumar et al., 2001) to revive the same approach and with claims of an analogous result for the rainfall-runoff process, we think it is necessary to clarify why this approach can be easily misleading. At the same time, we ask which chaos is involved in the rainfall-runoff process and what are the prospects for its modelling?

Determination of recharge in unsaturated soils using temperature monitoring

Can shallow temperature measurements on vertical profiles be used to determine the recharge? As a first approach to answer this question, we consider here the soil temperature data recorded by meteorological stations. A group of annual cycles allows us to determine the average value of vertical water seepage: in the presence of infiltration the apparent diffusivity deduced from the damping of the amplitude of the temperature between two different depths differs from the apparent diffusivity deduced from the temperature phase shift between the same pair of depths, and the average water flow can be easily deduced from this difference. For the determination of recharge over shorter periods of time it would be better to reconsider the sampling step of the data in both time and space domains. These limitations can be overcome by installing specialized vertical temperature profiles.

Riparian wetlands of the middle reach of the Seine river (France): historical development, investigation and present hydrologic functioning. A case study

Along the middle reach of the Seine river, upstream from Paris, riparian wetlands that have been functioning for centuries, first as a result of a succession of sedimentological/hydrological processes and later of continuous management practices where the value of the wetlands has been acknowledged as well as their importance for the ecology. Here, we present the results of a multidisciplinary research programme focused on this system with emphasis on its present hydrological functioning and on the tools used to understand and quantify it. The major hydrological and geochemical processes that are active at present are reviewed, but past processes are also described as well as the potential long-term evolution of the system. This study uses several innovative tools to investigate the wetlands and analyse them in space: thermographic aerial survey and electromagnetic prospecting resulting in a map of clay-layer thickness. Concerning the wetland hydrology, water budgets, established at different time scales (several years, one year, a season) illustrate the exchanges between the watershed, the river and the wetland and water storage in the wetlands during flood events. The results show how the upstream reservoirs, built during the last 20 years, presently control the preservation and functioning of downstream riparian wetlands. Monitoring and modelling of the hydrological functioning of one wetland site have made it possible to identify and quantify exchanges between the wetland (especially in the unsaturated upper layer) and its environment. In situ measurements of denitrification rates in the wetland were used to make initial estimates of its nitrate-elimination capacity.

Interprétation multifractale des courbes intensité-durée-fréquence des précipitations

Intensity-duration-frequency curves, which are very useful for many design applications, are generally empirically drawn from point rainfall time series. Such point time series can also be analyzed from a multifractal point of view and universal parameters characterizing the series can be estimated from empirical data. We derived from the scale invariant relationship of multifractals the formal equations of intensity-duration-frequency curves, which depend on only a small number of the series multifractal parameters. A rational basis is thus given to these curves, which can be related to some objective parameters.

Quantification des écoulements nappe-gravières, en zone alluviale, par optimisation du bilan hydrologique

Abstract Understanding of groundwater flow across gravel-pit lakes/alluvial aquifer interfaces is necessary to assess solute fluxes. Groundwater flow and permeabilities were estimated for a five gravel-pit lake system situated near the Seine river upstream of Paris (France), using water balance modelling parameter optimization. Results agree with the available information on the studied medium. The method is satisfying, because estimated parameter uncertainty is found to be lower than 12 % for three lakes and under 40 %for the two others; probably in relation to our unprecise knowledge of external inflows.