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Modelling of flow and phosphorus transport in variably saturated soil in a peri-urban settlement in Kampala, Uganda
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Management and Assessment.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Management and Assessment.
(English)Article in journal (Other academic) Submitted
URN: urn:nbn:se:kth:diva-24567OAI: diva2:352096
QS 20120327Available from: 2010-09-17 Created: 2010-09-17 Last updated: 2012-03-27Bibliographically approved
In thesis
1. Environmental sanitation situation and solute transport in variably saturated soil in peri-urban Kampala
Open this publication in new window or tab >>Environmental sanitation situation and solute transport in variably saturated soil in peri-urban Kampala
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The environmental sanitation situation in Kampala’s peri-urban areas was reviewed and investigated through field studies, structured interviews with personnel from key institutions and administration of questionnaires to households in a selected peri-urban settlement (Bwaise III Parish).  In this settlement, specific field and laboratory measurements were undertaken so as to create a better understanding of the environmental sanitation situation, anthropogenic pollution loads and their transport and impact (with a focus on Phosphorus) in Kampala’s Peri-urban areas in pursuit of interventions for improving the environmental sanitation and protecting the shallow groundwater resource there. The review revealed that the urban poor in Kampala, like elsewhere in developing countries, are faced with inadequate basic services caused by a combination of institutional, legal and socio-economic issues and that the communities’ coping strategies are in most cases detrimental to their health and well-being. Field surveys showed that excreta disposal systems, solid waste and greywater are major contributors to the widespread shallow groundwater contamination in the area. Field measurements revealed that the water table responds rapidly to short rains (48 h) due to the pervious (10-5-10-3 m/s) and shallow (<1 mbgl) vadose zone, which consists of foreign material (due to reclamation). This anthropogenically influenced vadose zone has a limited contaminant attenuation capacity resulting in water quality deterioration following rains. The only operational spring in the area is fed by regional baseflow meaning a wider protection zone. The spring discharge exhibited microbial quality deterioration after rains primarily as a result of poor maintenance of the protection structure. Subsurface phosphorus (P) transport mechanisms appeared to be a combination of adsorption, precipitation, leaching from the soil media and through macropore flow with the latter two playing an important role in the wet season. The Langmuir isotherm described the phosphorus sorption data well (R2³ 0.95) and the best prediction of Langmuir sorption maximum (Cmax) had organic carbon, Ca and available phosphorus and soil pH as significant predictors. Loosely bound P (NH4Cl-P) was the least fraction (<0.4% of total P) in all layers indicating a high binding capacity of P by the soils implying that the soils have a capacity to adsorb additional P loads. Simulation results from the preliminary numerical model built in this study based on field and laboratory measurements indicate that rainfall infiltration rates > 7x10-3 mm/s drive shallow groundwater contamination with higher intense rains of relatively longer duration (³ 70 mm within 48 h) reducing phosphorus transport. Sensitivity analysis of the model input with respect to how long it takes to pollute the subsurfacehad the phosphorus sorption coefficients as being more influential than the pore size and air entry values. There are however, key contrasts between the model simulations and field observations which are useful in guiding new efforts in data collection. The study reveals that intervention measures to improve the environmental sanitation and protect the shallow groundwater in the peri-urban settlements are of a multidisciplinary nature necessitating action research with community participation.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xiv, 60 p.
Trita-LWR. PHD, ISSN 1650-8602 ; 1059
Environmental Sanitation, Kampala, Modelling, Phosphorus transport, Shallow groundwater, Peri-urban, Vadose zone
National Category
Other Environmental Engineering
urn:nbn:se:kth:diva-24595 (URN)978-91-7415-728-4 (ISBN)
Public defence
2010-09-30, Makerere University, Uganda, 09:15 (English)
QC 20100917Available from: 2010-09-17 Created: 2010-09-17 Last updated: 2010-12-01Bibliographically approved

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