Assessment of groundwater risk using intrinsic vulnerability and hazard mapping: Application to Souassi aquifer, Tunisian Sahel

Special attention has been paid to risk assessment in water resource management in arid and semi-arid regions like the Souassi aquifer, Tunisia. Risk assessment, using vulnerability and hazard mapping, is considered as a fundamental aspect of sustainable groundwater management. To determine the degree of risk affecting the study area, an attempt has been made to combine hydro-geologic parameters using the DRASTIC method and the hazard assessment by taking the product of the weighted hazard value (H_I), the ranking factor (Q_N) and the reduction factor (R_f).All parameters used in this risk assessment were prepared, classified, weighted and integrated in a GIS environment. Data treatment shows that large areas in the Souassi aquifer can be classified as high or very high risk areas corresponding to pollution sources located in high vulnerability zones. The areas with low and very low risk are situated in the south, which could, consequently, be interesting for future development and long term planning of protective measures. Sensitivity analyses indicated that the removal of groundwater depth, net recharge and aquifer media parameters from the DRASTIC index, causes large variation in vulnerability assessment. Moreover, hydraulic conductivity and topography were found to be more effective in assessing aquifer vulnerability. Therefore, they should have higher weights than those assumed by the DRASTIC standard method, and contrary to the impact of the vadose zone parameter. The validity of the DRASTIC and the risk methods, verified by comparing the distribution of nitrates in the groundwater and the different vulnerability classes, shows a high similarity.     

Sustainability of tunnel wells in a changing agrarian context: A case study from South India

We analyze tunnel wells (surangams), traditional water harvesting systems, which have been innovated and nurtured by farmers in the Enmakaje panchayat in the state of Kerala in South India for decades. We show how the genesis and design of the indigenous knowledge-based water harvesting systems are shaped by agro-ecological conditions. We also identify issues that affect the sustainability of tunnel wells in the changing agrarian context in this region. The significance of tunnel wells is declining, even though the smallholders, who dominate the agricultural landscape, are highly dependent on tunnel wells to meet their water requirements. Grass roots efforts are needed to revive this traditional water harvesting system.     

A new approach to water management of tropical peatlands: a case study from Malaysia

The use of peatlands in the humid tropics requires drainage to remove excess rainfall. The design principles for the drainage systems currently being implemented on peatlands are the same as for mineral soils. The objective of such systems is the timely removal of excess rainfall by surface runoff. For peatlands, with their different soil-hydraulic characteristics, these systems have resulted in poor watertable control and high rates of irreversible subsidence. Concerns about this rate of subsidence and the level of sustainability of the present land use have prompted a study to develop a new water management system. This new system includes a shift from a drainage system that focuses on discharge of excess water towards a system that combines drainage and water conservation. In the new two-step design, the drain spacing and corresponding drain discharges are obtained with a steady-state approach. These outputs are used to calculate the capacity of the drains, including control structures, using an unsteady-state approach. The new system results in a shallower but more narrowly spaced drainage system and maintains a more constant but relatively high watertable and reduces subsidence. It should be remembered however, that even with the improved water management, subsidence cannot be arrested; it is the price one has to pay for the use of tropical peatlands.     

Nutrient losses associated with irrigation, intensification and management of land use: A study of large scale irrigation in North Otago, New Zealand

Irrigation of pasture enables the intensification of land use, but can also result in increased losses of nitrogen (N) and phosphorus (P). In 2006 an irrigation scheme was introduced into the Kakanui River and Waiareka Creek catchments in North Otago, New Zealand, which has intensified land use, especially dairying. Supplementation of the Waiareka Creek by direct discharge of ‘clean’ irrigation water from a nearby River is practiced to raise the minimum flow. This supplementation is hypothesized to dilute N and P losses associated with increased land use intensification and irrigation return flow. Farm losses of N and P before irrigation were then used as a reference to judge in the Kakanui River, and compare against dilution in the Waiareka Creek, the effectiveness of best management practices (BMPs) to improve water quality in 2010 and 2020. Data for N and P fractions from three sites since the mid 1990s were analysed, and flow adjustments for direct discharge to the Waiareka Creek made. Similar concentrations of N and P fractions in Waiareka Creek before and after irrigation began suggest the current minimum flow of 100 L s⁻¹ is insufficient to improve the nutrient status of the Creek, but does dilute recent intensification, which without dilution would have increased concentrations by 30-400%. In the lower Kakanui catchment, direct discharge does not occur and N and P concentrations increased, while little change occurred in the upper Kakanui catchment. Within each catchment, N and P losses from sheep and beef farms and dairy farms (with and without BMPs) were modelled for 2010 and 2020 and compared against that estimated in 2000. This showed that although substantial decreases could be made by adopting BMPs, the predicted increase in N and P losses (up to 200% by 2020) would require either more rigorous use of existing strategies or additional strategies to improve water quality, over and above dilution which is restricted by a need to minimise the risk of flooding.     

A study of water distribution from a branch to distributary canals: A case study of Gugera Branch,Punjab, Pakistan

This study was conducted on Gugera Branch of Lower Chenab Canal, Punjab, Pakistan. Sample distributaries off taking from Gugera Branch were selected for the study. The existing conditions of water distribution among the distributaries were studied. Field data were collected during the whole of 1988. Field observations suggested that the variability at the head of distributaries is much greater than the variability in the Gugera Branch under existing operational practices. The distribution of water among the distributaries is rarely in accordance with design criteria. Some channels get priority over other channels. The annual closure period varied from 17 to 41 days for different channels. The discharge at the head of distributaries remained lower than the standard operational range for 69 to 183 days in a year. The data suggested that a regulating gate at the head of the distributary can reduce discharge variation up to 2.4 times compared with a Karrees System (wooden stop logs used for water regulation). The data indicated that the adjustments in the head gate of a distributary on daily basis can substantially improve discharge conditions at the head of distributary. Rotational schedules are not being followed as per design and need to be improved. Most of the existing head discharge relationships of discharge measuring structures are not reliable. A frequent calibration of these structures is recommended.