The role of remote sensing in hydrological modelling of the Okavango Delta, Botswana (original) (raw)
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The Okavango Delta is one of the world's most fascinating wetland systems. The highly dynamic flooding forms the basis for a multitude of different ecosystems and plant and animal communities. Water scarcity and economical development lead to an increasing pressure on the ecosystem. A hydrological model is being developed to help making management decisions more sustainable by simulating possible impacts. The model can simulate anthropogenic changes such as water abstraction, damming, dredging and climate change. A key input parameter for the hydrological model is the topography, particularly the statistical properties of the topographic variability. These properties can be quantified using aerial remote sensing data.
Regional review: the hydrology of the Okavango Delta, Botswana—processes, data and modelling
Hydrogeology Journal, 2009
The wetlands of the Okavango Delta accommodate a multitude of ecosystems with a large diversity in fauna and flora. They not only provide the traditional livelihood of the local communities but are also the basis of a tourism industry that generates substantial revenue for the whole of Botswana. For the global community, the wetlands retain a tremendous pool of biodiversity. As the upstream states Angola and Namibia are developing, however, changes in the use of the water of the Okavango River and in the ecological status of the wetlands are to be expected. To predict these impacts, the hydrology of the Delta has to be understood. This article reviews scientific work done for that purpose, focussing on the hydrological modelling of surface water and groundwater. Research providing input data to hydrological models is also presented. It relies heavily on all types of remote sensing. The history of hydrologic models of the Delta is retraced from the early box models to state-of-the-art distributed hydrological models. The knowledge gained from hydrological models and its relevance for the management of the Delta are discussed.
Modelling of the flooding in the Okavango Delta, Botswana, using a hybrid reservoir-GIS model
Journal of Hydrology, 2006
The Okavango Delta is dominated by annual flood events from the Okavango River. During such events the inundated area increases from about 5000 km 2 to 6000-12,000 km 2 . Several models of a conceptual character were developed previously to represent hydrological processes in that system. Although essentially successful in their applications, the models have been criticised for their conceptual simplicity and the arbitrary way of representing long-term variation in outflows. All the existing models required the use of correction factors to address the apparent non-homogeneity of the time series. This paper presents a new model that has overcome these shortcomings by introducing more physical knowledge of the Okavango Delta system into the model. In view of the spatial complexity of the system and lack of data to support spatially distributed parameterisation of hydrological processes, the semi-distributed semi-conceptual approach, based on large units, has been retained. The major improvements of the model are: a better representation of surface water-groundwater interactions and the use of measurement-based rather than model calibrated parameterisation of topographic controls of floodplain water storage. These enabled a successful representation of 34 years of observed outflows and 15 years of observed inundation area in a conceptually sound way. Additionally, a GIS model has been developed for determination of spatial distribution of the simulated floods. In this model, the within-unit flood distribution is obtained from remote sensingderived flood maps. In this way, in spite of the semi-distributed nature of the hydrological model, flood distribution maps and ecologically important flooding characteristics can be determined for simulated and predicted floods with a spatial resolution much higher than that of the computational units. The hydrological model developed forms the basis for subsequent analyses of ecosystem response to hydrological change of both floodplain and dryland ecosystems.
Dynamics of floodplain-island groundwater flow in the Okavango Delta, Botswana
Journal of Hydrology, 2006
Surface water-groundwater interactions play a crucial role in the hydrology and ecology of the Okavango Delta. The hydrology of the Delta is dominated by the annual arrival of a flood wave which is distributed over an number of branches. Subsequently, the flood water feeds the phreatic aquifers underlying the Delta islands. In order to evaluate the seasonal and long-term dynamics of the surface water-groundwater interactions between the floodplains and the islands, a network of piezometers located in various locations of the Delta was monitored. Groundwater table fluctuations observed for up to 6 years were analysed and modelled using groundwater flow models. The floodplain-island groundwater flow is in general very dynamic and driven by island evaporation and transpiration. A typical small to medium sized island (width !500 m), appear not to be influenced by long-term antecedent conditions. Only on large islands (width O500 m) and at the perimeter of the flooded area is the influence of long-term antecedent conditions apparent. The knowledge gained during this study will be used for the improvement of the hydrological and hydro-ecological model of the Delta, and can be useful for the description of floodplain dynamics in semi-arid regions in general. q
Journal of Hydrology, 2006
Changes in hydrological inputs to the flood-pulsed Okavango Delta result in changes in such flooding characteristics as floodplain water depth, inundation duration and frequency. A mathematical model is used to assess impacts of changing hydrological inputs on flooding in the Okavango Delta. Future conditions are simulated by superimposing simulated abstractions, upstream developments and climate change effects on the observed time series of hydrological inputs. The effects of change in inputs are then determined by comparing hydrological characteristics such as inundation duration and frequency derived from the original and modified time series of model outputs. Simulations show that upstream abstractions are likely to have small short-term effects on the flooding pattern in the Delta, while other upstream developments such as damming or deforestation have more pronounced effects. All of these effects are relatively small, however, when compared to changes resulting from existing climatic variability, and those from the possible effects of future climate change. The combined effects of human abstraction and climate change, manifested as increased temperatures, decreased rainfall, and reduction in river flows, may result in significant Delta drying. The simulated hydrological changes affect the Delta floodplain ecosystems, with anticipated changes in the area and proportions of permanent swamp, areas covered by sedge and grass vegetation (seasonal floodplains) and floodplain grasslands (intermittently flooded areas). These will have varied effects on ecological processes in the Delta, in particular vegetative succession, primary production, and relationships of floodplains with the surrounding woodland and savannah. Additional ripple effects up trophic levels can also be expected. There may also be downstream a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l
Water SA, 2007
The United States Soil Conservation Service (SCS) curve number method is used to estimate rainfall runoff from three sub-watersheds in SouthEastern Botswana. This approach uses the NASA Endeavour Shuttle Radar Topography Mission (SRTM) DEMs, digital soil data from the Botswana Ministry of Agriculture, rainfall data from the Department of Meteorological Services and land-use data derived from Landsat ETM+ imagery. Runoff predicted from the SCS method is compared with the runoff calculated using the Pitman and Monash models and the gauged runoff. The Thagale River system watershed produces a mean annual volume of 7.2 Mm 3 while the Notwane and Metsimotlhabe runoff volumes are 19.9 Mm 3 and 17.8 Mm 3 respectively. The SCS Model is found to be either over-or underestimating the mean annual runoff volumes found using the other two models. It is concluded that more mean annual runoff volumes should be established for the whole country using the three models and a correlation analysis made in order to determine the superior model. The SCS Model uses a lot of Earth Observation (EO) and other data found in different government departments, hence this encourages collaboration. It is further observed that the SCS Model is quick to produce results, does not require stream gauging and can also easily be updated as the land use/land cover changes.
Journal of Geography & Natural Disasters, 2017
In line with Climate change rainfall seasonal fluctuation and rainfall amount have major impact on flood and becoming a trait to human life and properties especially on agriculture and different installation. Therefore estimating the runoff and identifying flood prone area at different return period is very essential for effective flood mitigation measure. One of the possible approaches for identifying flood prone area is use of integration of RS with hydraulic models (HEC-RAS). The present study area is of Woybo River catchment, south western Ethiopia, Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM), 90 m resolution downloaded from united states geological survey, were used to extract the river geometry. Daily peak rainfall data from tow metrological stations (1990-2013), collected from national metrological agency, were used for estimating design rainfall and runoff for 5, 10, 25, 50, 100 and 200 return period. In HEC-RAS, river geometry, boundary conditions, manning's n value of different land cover, designed runoff for different return periods were inputted then steady flow analysis was carried out. estimated design rainfall frequency showed expected peak rainfall were 63.
Using Remote Sensing Data to Model Groundwater Recharge Potential in Kanye Region, Botswana
2011
This study focuses on the groundwater recharge potential in the upper Limpopo catchment starting from Kanye region in South Botswana. Existing high resolution remote sensing data were used to estimate the spatial distribution of potential recharge and discharge of aquifers in this semi-arid region. 29 NOAA AVHRR images available for Southern and Central Botswana between 1996 and 2000 were analyzed to produce 29 K c maps. The comparison of K c maps in wet and dry seasons shows similar patterns over the upper Limpopo catchment in Kanye region. The conclusion can be drawn that the K c pattern does not significantly change with time over the region. Therefore the time averaged K c map can be used together with a map of potential evapotranspiration to calculate actual evapotranspiration for the period 1996-2005. Ten year averages of actual evapotranspiration and precipitation together with the averaged discharge of the catchment to the Limpopo River are then used to calculate a potential...