Developing Design Storm Hydrographs for Small Tropical Catchments with Limited Data

Hydrographs are vital tools in the design and construction of water-control structures in urban and rural systems. The purpose of this study was to explore the development of design storm hydrographs for the small tropical catchment with limited data. In this study, Clark’s Unit Hydrograph method was used to develop synthetic hydrographs for the University of Ilorin Agricultural and Biosystems Engineering field plot. This method was selected for evaluation because the field plot has very limited stream flow data. Kunrun stream, which is the discharge outlet for the watershed, has no gauge stations. Clark's method was evaluated in this study for peak discharge and storm hydrograph analysis of the field plot. The total area of the field plot measures 18.4 ha and is characterized according to its land use: pasture range land (34%), cultivated land (49%), wood or forest land (9%) and 'dirt' (8%). The three necessary inputs needed for the development of the synthetic hydrograph using Clark’s method are: time of concentration, a storage coefficient, and a time-area histogram. The  time of concentration was estimated using the Natural Resources Conservation Service method (NRCS) with the lag time determined from Snyder’s equation. The storage coefficient was estimated at 0.75 hr while the time of concentration was 1.98 hr. Convolution procedures were used in determining the storm hydrograph from the unit hydrograph. Runoff volume and peak discharge from the unit hydrograph were estimated to be 2.4 x 104 m3 and 1.02 m3/s, respectively. According to the 24hour, 100year storm hydrograph, the runoff volume was 5.23 x 104 m3 while the peak discharge was 2.15 m3/s. It was found that Clark's Unit Hydrograph Method was very suitable in the development of design storm hydrograph for small tropical catchment with limited data.Keywords: Clark’s unit hydrograph, Storm hydrograph, Peak discharge,  ungauged watershed

Stochastic Analysis of Rainfall Events in Ilorin, Nigeria

This paper reports on a stochastic analysis of rainfall events in Ilorin, Nigeria. Rainfall, the most common form of precipitation in most parts of the world, is a principal component of the hydrologic cycle. Rainfed agricultural practices dominate agricultural activities in Ilorin, which could be enhanced by accurate predictions of rainfall attributes. Since rainfall exhibits natural variability, its analysis in a stochastic framework provides a more realistic premise. Five probability distribution namely the normal, lognormal, logPearson typeIII exponential and extreme value type I distributions – were used in this study because of their desirable properties. The analysis was based on 41 years of daily and monthly rainfall data (1955-1995) for Ilorin, with peak values computed for each year.Weibull plotting positions and the number of rainy days were also determined. September had the highest number of rainy days, followed by June. Rains are least expected in Ilorin in January and December. The maximum daily rainfall has a mean depth of 85mm and a standard deviation of 28mm while the corresponding values for the maximum monthly rainfall are 275mm and 56mm. The logPearson type III distribution best suited the maximum daily rainfall data while the normal distribution best described the maximum monthly rainfall for Ilorin. JARD Vol. 1 2001: pp. 39-5

Modeling Soil Temperature Variations

This paper reports on modeling soil temperature variations. Transient heat flow principles were used in the study, with the assumptions that the heat flow was one-dimensional, the soil was homogenous and that the thermal diffusivity was constant. Average conditions are also assumed. The annual and diurnal (daily) soil temperature cycles were modeled with fairly good accuracy. Differences in measured and predicted soil temperatures were determined at the annual level at depths 0cm (surface), 5cm, 10cm, 20cm, 30cm, 50cm and 100cm while the differences were determined at the diurnal level at depths 5cm, 20cm and 30cm at 9a.m and 3p.m. For the annual cycle; the lowest average absolute error (1.230C) was obtained at the soil surface, with the highest average error (3.520C) obtained at the 10cm soil depth. For the diurnal cycle; the average error was 1.070C at 9am while it was 3.670C at 3p.m. The damping depths for the study area (Ilorin) were 224cm, 12cm and 2cm for the annual, diurnal and hourly cycles, respectively.. JARD Vol. 2 2003: pp. 100-10

An appraisal of safety of tractor-trailer braking system

The tractor-traller braking system was appraised considering the effect of braking the tractor or trailer alone and also braking the combination of tractor and trailer simultaneously. The study became Imperative  considering the Influx of trailers that are not equipped with the braking system and the danger It poses to the operators and the fann produce. The study employed simple field slmulatlon of the behaviour of each model and further analysis of the system. The result showed that It would be In the best interest of any country Importing agricultural trailers to import those equipped with braking system which could be actuated by the hydraulic control of the tractor. This would reduce to the barest minimum dangers associated with operators of tractor-trailer systems, tyres and loss or damage to produce being transported.Keywords: Tractor, Trailer, Slmulatlo

Spreadsheet modelling of unit and storm hydrographs for ungauged watersheds

This paper describes a spreadsheet model developed for deriving both unit and storm hydrographs for ungauged watersheds based on the Soil Conservation Service (SCS) method. Essentially, the model implements computational procedures that involve developing a 1-hour unit hydrograph for a given ungauged watershed, then applying it to estimate 1hour incremental rainfall excess to derive a design storm hydrograph through the convolution technique. The model, which is intended to remove computational drudgery in several calculations that are involved in the synthetic unit hydrograph derivation, excess rainfall estimation and hydrograph convolution, was applied in deriving a 1-hour unit, 25-yr, 24 hr and 100-yr, 24 hr storm hydrographs for an ungauged watershed of the Department of Agricultural Engineering, University of Ilorin, Ilorin, Nigeria. The weighted curve number and the potential maximum storage of the watershed estimated by the model were 73 mm and 94 mm respectively. The model computed the watershed’s lag time and time of concentration as 0.25 hr and 0.42 hr. The peak flow from the unit hydrograph was 0.05 m3/s at time to peak of 0.8 hr while the 25-yr, 24 hr and the 100-yr, 24 hr storms had peak flows of 1.73 m3/s and 2.38 m3/s, at times to peak of 1.20 hr and 1.12 hr respectively. This work will enhance the computational efficiency in unit and storm hydrograph development.Keywords: Spreadsheet modelling, Unit hydrograph, Storm hydrograph, Ungauged watershedsJournal of Applied Science, Engineering and Technology, Volume 8, 200