This study investigates the flood impact of precipitation increase and land use change inLagos megacity. It simulates the runoff, peak flow and area inundated for different climate change scenarios on systems 1, 2 and 5. This was achieved by using Precipitation Water Inundation Model (PWIM) that integrates projections of precipitation from regional models and urbanization drivers from land use change to analyse future flood scenario of 25 years and 50 years return periods. Using 2008 as base year, future climate scenarios of 50 and 100 years medium and high changes were analysed for three urban catchments in Lagos (system 1, system 2 and system 5). The urbanization driver of transforming storm runoff to flood in central Lagos was determined using trend analysis while projection of precipitation driver was based on statistical downscaling of CAM-EULAG regional climate model. The results revealed that runoff and peak flow on system 1 will increase by 6.34%, 14.24%, and 20.36% for 50 years medium climate change MCC, 50 years high climate change HCC and 100 years HCC respectively, 10.88%, 13.52%, and 19.26% for 50 years MCC, 50 years HCC and 100 years HCC respectively on system 2 and 6.13%, 13.31%, and 18.91% for 50 years MCC, 50 years HCC and 100 years HCC respectively on system 5. On the average, 20% to 25% increase in urban flash flood due to high climate change will be recorded in the next 50 – 100 years. Adaptation and Mitigation measures through urban renewal and integration of future fluxes from climate change are imperative in reducing the vulnerability of people and property to flooding in Lagos.
Key words: Urban Flooding, Climate Change, Lagos
Effects of landuse changes on the sedimentation rate in the Galma Reservoir in Northern Nigeria
Abu, R. D.
Department of Geography, Ahmadu Bello University, Zaria.
The Galma earth dam was impounded in 1975 to supply Zaria with drinking water and has a maximum storage capacity of 16 million cubic metres, a maximum depth of 14.9m, a dam length of 640m and a total lake length of 40km. The intensification of cultivation, fuel wood harvesting and other landuses within the catchment of the Galma has resulted in increased soil erosion. This study was carried out with the objective of determining the effects of the present landuse/landcover change on the sedimentation rate of the Galma dam. To achieve this objective, Landuse / land cover changes over the catchment of river Galma were assessed from Landsat MSS 50m resolution (resampled) for the 1970s; Landsat TM 30m resolution for the 1980s; SPOT XS 20m resolution for the 1990s and Landsat ETM 15m resolution for the 2000s.The results reveal that cultivated area increased from 2476.25km2 to 3241.36km2; built-up area from 4.06km2 to 13.67km2 from 1970s to 2000s respectively while forest and water body show a reduction of 1085.35km2 to 313.52km2 and 7.12km2 to 5.81km2 from 1970s to 2000s respectively. Area statistics of 203.25km2 was uniform for rock outcrop throughout the decades of 1970-2000. Hydrographic survey of the dam was conducted to determine the level of sedimentation by carrying out depth measurement of the dam from the surface to its bed .The result obtained shows that the dam has lost 7.6m depth to sedimentation; indicating 51% loss in installed storage capacity. The results have significant implications for future water supply to the residence of Zaria.
This paper presents the estimation of runoff in an ungauged watershed in Chanchaga River Basin in Guinea Savannah region using semi arid moisture balance technique (SAMBA). The SAMBA model is a single layer soil water balance model that estimates daily surface runoff using daily rainfall, evapotranspiration, vegetal cover and soil moisture deficit (SMD). The model estimate was validated with discharge measurements taken in 2009 and 2010 with a rectangular weir across a stream at the outlet of the basin. Annual runoff for the year 2009 was 167.7 mm, which is 14.5% of the annual rainfall of 1157.1 mm. Maximum runoff occurred on 1st September, coinciding with the high rainfall that occurred between 29th August and 1st September. Similar result was obtained for the year 2010. It was also found that SMD was as high as 49.8 mm during the dry season. The result is useful in understanding and management of water resources in the region.
Modelling daily flows of River Benue using Artificial Neural Network approach
Otache, Y. M., Mohammed, A. S., Ahaneku, I. E. and Egharevba, N. A.
Department of Agricultural & Bioresources Engineering,
Federal University of Technology, Minna, Nigeria
The importance of understanding the dynamics and forecasting of streamflow processes of a particular river finds relevance in the fact that the physical mechanisms governing flow dynamics act on a wide range. In view of this, this study presents a simple basis for and application of Artificial Neural Network (ANN) methodology as an alternative modelling tool for predicting flow. To this end, the main focus is the development of ANN model for short term streamflow forecasting of the Benue River using univariate time series; inter alia, evaluate its performance of extreme events. It is evident from the modelling framework that the application of the knowledge of evolution of a dynamical system in a multi-dimensional state space is a robust approach for determining the size of an ANN model input.The ANN model forecast performance showed that reliable short term forecasts, 5 day – ahead can be made for the daily streamflow series based on CE and R2 performance indexes. However, on the general question of the suitability of ANN model application for streamflow forecasting as applied in this study (i.e., daily streamflow), though the neural network could simulate the different attributes of the flow hydrograph, its relative forecast performance of high flows is robustly better than the case of low flows; it grossly under predicted and over predicted same depending on the particular network input data pre-processing schema. The forecast performance results also indicated that, for feed-forward MLP networks, with a tan-sigmoid transfer function, standardising the data by subtracting the mean and dividing by the standard deviation is better than rescaling the data to a small interval of particular range. Considering the findings, to appropriately capture the dynamics of the flow regime, it is necessary to include exogenous variables of the runoff generating process in the network input data base.
Department of Geography, Benue State University, Makurdi, Nigeria
(ocherix @ yahoo.com)
The physico-chemical and bacteriological properties of water from hand dug wells in Oju town is examined in this study. A total of fifteen hand dug wells were sampled across the three residential areas of the town in the month of August, 2010. Water samples were analysed according to standard methods of examination for water and reported based on Nigerian Standard for Drinking Water Quality (NSDWQ). This involves in-situ, field determination using meters and laboratory techniques such as titration and atomic absorption spectrophotometric methods of analysis. The result of analyses shows that iron, nitrates and bacteria concentrations exceed the NSDWQ standard in some hand dug wells. Other parameters like pH, temperature, turbidity, electrical conductivity, total dissolved solids, total hardness and chloride were within the NSDWQ standard. The high concentration of iron, nitrates and bacterial contamination is attributed to shallow well depth, distance to latrine/soak away, improper well construction as well as land use. This has rendered the water unsafe for drinking. It is therefore recommended that hand dug well water should be disinfected by the use of adequate volume of water guard as well as other water purifier to ensure its safety.
Key words: Hand dug wells, physico-chemical, bacteriological, Water quality, Oju town
Lysimeter Study of Crop Evapotranspiration of African Spinach
in Nsukka, Southeast Nigeria
Okechukwu, M. E. and Mbajiorgu, C. C.
Department of Agricultural and Bioresources Engineering,
Faculty of Engineering, University of Nigeria, Nsukka
A drainage lysimeter of 2m surface area with a depth of 1m was used to estimate the crop evapotranspiration of African spinach (Amaranthus Cruentus) in Nsukka southeastern Nigeria between mid February and mid March 2011. The crop was irrigated daily using a watering ca, and the lysimeter was instrumented to monitor rainfall, drainage, and soil moisture. The daily data generated were used to evaluate crop evapotranspiration (Etc) from the water balance equation. The crop evapotranspiration determined from the lysimeter for African spinach was 185.37mm, for the period with an average daily crop evapotranspiration of 5.98 mm/day. This compares favourably with the FAO Penman Monteith method which gave an average daily ETc of 6.08 mm/day for the same period.