Groundwater recharge and age-depth profiles of intensively exploited groundwater resources in northwest India

Intensive irrigation in northwest India has led to growing concerns over the sustainability of current and future groundwater abstraction. Environmental tracers and measurements of groundwater residence times can help quantify the renewal processes. Results from 16 paired locations show the interquartile ranges for residence times in shallow alluvial groundwater (8–50 m deep) to be 1–50 years and significantly less than those from deeper groundwater (76–160 m deep) at 40–170 years. The widespread occurrence of modern tracers in deep groundwater (>60% of sites had >10% modern recharge) suggests that there is low regional aquifer anisotropy and that deep aquifers are recharged by a significant component of recent recharge via vertical leakage. Stable isotope and noble gas results at all depths conform to modern meteoric sources and annual average temperatures, with no evidence of significant regional recharge from canal leakage in this study area close to the Himalayas

Complementary methods to investigate the development of clogging within a horizontal sub-surface flow tertiary treatment wetland

A combination of experimental methods was applied at a clogged, horizontal subsurface flow (HSSF) municipal wastewater tertiary treatment wetland (TW) in the UK, to quantify the extent of surface and subsurface clogging which had resulted in undesirable surface flow. The three dimensional hydraulic conductivity profile was determined, using a purpose made device which recreates the constant head permeameter test in-situ. The hydrodynamic pathways were investigated by performing dye tracing tests with Rhodamine WT and a novel multi-channel, data-logging, flow through Fluorimeter which allows synchronous measurements to be taken from a matrix of sampling points. Hydraulic conductivity varied in all planes, with the lowest measurement of 0.1 md1 corresponding to the surface layer at the inlet, and the maximum measurement of 1550 md1 located at a 0.4m depth at the outlet. According to dye tracing results, the region where the overland flow ceased received five times the average flow, which then vertically short-circuited below the rhizosphere. The tracer break-through curve obtained from the outlet showed that this preferential flow-path accounted for approximately 80% of the flow overall and arrived 8 h before a distinctly separate secondary flow-path. The overall volumetric efficiencyof the clogged system was 71% and the hydrology was simulated using a dual-path, dead-zone storage model. It is concluded that uneven inlet distribution, continuous surface loading and high rhizosphere resistance is responsible for the clog formation observed in this system. The average inlet hydraulic conductivity was 2 md1, suggesting that current European design guidelines, which predict that the system will reach an equilibrium hydraulic conductivity of 86 md1, do not adequately describe the hydrology of mature systems

Upscaling Flow and Transport Processes

Peer reviewe

Quantification of preferential flow and flow heterogeneities in an unsaturated soil planted with different crops using the environmental isotope δ¹⁸O.

We present a method to quantify preferential flow in the unsaturated zone of cropped soils. This method was developed for bare soils (Stumpp et al., 2007) and is now applied to a lysimeter containing an undisturbed soil monolith planted with different crops. The lysimeter experiment was operated under natural atmospheric conditions over more than 5 years. The mean precipitation was equal to 953 mm/a while the mean outflow was 538 mm/a. Preferential flow was quantified with a two component flow approach using hydrological data and stable isotope contents (δ18O) as tracer, which were measured in precipitation and discharge. The results of the tracer transport modelling with a numerical transient and with a lumped dispersion model from a previous study (Stumpp et al., 2009b) were used here to evaluate the differences between the total and matrix flow. The application of the two component mixing approach yielded a mean preferential flow rate of 0.85 mm/week and 0.42 mm/week using a transient numerical and lumped parameter approach, respectively. However, except of some few events, preferential flow was found in the same weeks independently on the model approach. The amounts showed a seasonal variation that was explainable by the vegetation cover. Directly after harvest and before sowing the highest rates of preferential flow were observed that decreased during the plant growth periods. In mean 1–3% or 4–6% of the precipitation amount, which corresponds to 2–5% or 7–10% of the discharge, was flowing preferentially through the soil depending on the vegetation by applying transient and lumped approaches, respectively. Finally, the results from the lumped parameter modelling were used to construct vegetation specific vulnerability diagrams. These diagrams give information about flow heterogeneities and show the transit time distribution functions and water balance for the different vegetations

Mathematical models for interpreting tracer experiments in fissured aquifers.

A model of parallel fissures with equal spacing and instantaneous input has been further exploited to show its applicability to the interpretation of short term tracer experiments. The problems encountered with solute transport in long term tracer experiments are also discussed. It is shown theoretically that the 14C age in fissured carbonate formations does not yield correct flow parameters