The Sensitivity of Evapotranspiration Models to Errors in Model Parameters

Five evapotranspiration (Et) model-the penman, Blaney - Criddel, Thornthwaite, the Blaney –Morin-Nigeria, and the Jensen and Haise models – were analyzed for parameter sensitivity under Nigerian Climatic conditions. The sensitivity of each model to errors in any of its measured parameters (variables) was based on the relative error introduced by the parameter in the predicted Et at various perturbations of the parameter. Three levels of sensitivity, herein termed sensitivity, ratings, were established, namely: Highly Sensitive (Rating:1); Moderately sensitive’ (Rating:2); and ‘not too sensitive’(Rating: 3). The ratings were based on the amount of error in the measured parameter to introduce + 10% relative error in the predicted Et. The level of importance and the care required in the measurement of each parameter with respect to the model in which it occurs are therefore established

The Role of Undercutting of Banks in the Collapse and Evolution of Small Channels

The influence of undercutting in rill banks on the development and collapse of rill banks and on the subsequent evolution of the rill channels were investigated in a laboratory flume. Undercutting of rill banks were observed to develop in rill channels by 'reverse roller' effect of plunging water jet into scour holes, cutting the underside of the head cut wall. The extent of undercutting and the rate of drawdown of water into the rill influenced the collapse of the rill wall. Slumping was the predominant mode of failure of rill banks from this study, although other types of failures were observed. The type and mode of failure determined the amount of soil that collapsed into the rill. This in turn greatly influenced the evolution of the rill channel. Rill bank collapse was observed to contribute as much as 53% of the total sediments from the rill. It is therefore emphasized that its effect be included in present-day process- based rill erosion models

Soil Groups Relative Susceptibility to Erosion in Parts of South-Eastern Nigeria

Insitu rainfall simulator runs were carried out on 15 soil groups located in various parts of South Eastern-Nigeria, namely Abia, Ebonyi and Imo States of South- eastern Nigeria. The tests were carried out under 'dry' and 'wet' soil conditions, each at rainfall intensities of 40, 60, and 90mmlhr. The resulting soil losses were analysed, and the relative susceptibility of the various soil groups to erosion by water determined based on the amount of soil lost during the various runs. Based on the 'erodibility ratings' the soils were finally categorised into 'moderately erodible', 'highly erodible', and 'very highly erodible' The moderately erodible (under wet run considerations), include Typic Dystropepts, (from sand stone), Gross Arenic Paleudult, Eutric Tropofluents, and Aquic Paleudult. The highly erodible include Typic. Tropaquept (Eutric Gleyso1s), Plinthic Tropudult, Arenic Ptdeudalt, Typic Tropoudult (Dystric ferralsol), and Orthoxic Tropudult (Rhodic Ferralsol). The very highly erodible erodible include Typic Dystropepts (from shale), Typic Tropudult (Orthic acrisol), Typic Tropudalf, Typic Hapludult, Orthoxic Tropudult (Dystric ferralsol), and Typic Tropaquept (Dystric Gleysol}. These groupings agree to some extent with those under the 'dry run’ condition.

Determination of Design Inflow Rate in Furrow Irrigation Using Simulated Advance and Recession Curves

Advance and recession curves were simulated for three stages of maize growth in furrow irrigation. The selected stages were: the emergence stage, two weeks after planting; the development stage, about two months after planting; and the maturing stage, about one month to harvest time. The advance and recession times were predicted for successive points along the furrow lines for various inflow rates at the development stage of the crop growth using three models. The simulated advance and recession data were used to compute the intake opportunity time distribution along the furrow line. The infiltrated depth distribution and hence the water application efficiency and distribution uniformity were computed for the inflow rate, which gave 87% and 89% for the maize emergence stage: 75% and 60% for the maize development stage and 95% and 89% for the maize maturing stage. The design inflow rate for each furrow was taken as the minimum inflow rate which gave rise to a minimum water application efficiency of 60% and a minimum distribution uniformity of 75%. It is recommended that the procedure described in this work is useful for the modification of existing furrow irrigation systems and the establishment of new ones. Also, the design procedure presented can be used for any field that is suitable for furrow irrigation system by making use of the relevant parameter estimates that can be obtained from the field

Classification of Surface Water Sources in Imo State, for Irrigation Purposes, with Respect to Salinity and Sodicity

Surface water sources such as lakes, rivers and streams abound in Imo state. Such water resources can be developed for irrigation practice. To do this, irrigation quality status of such waters must be established. This study determined the salinity and sodicity status of eleven rivers in Imo State with a view to classifying them according to their suitability for irrigation based on already existing standards for such classification. The result showed that seven rivers: Imo, Iyodo, Ogochie, Okitankwo, Oramiriukwa, Orashi, and Otamiri rivers were classified under the C1-S1 irrigation suitability class, while four rivers:  Abadaba, Mba, Nworie and Onuiyin were classified under the C2-S1 suitability class. Implications of these classes for the rivers in Imo State with respect to how they may be used for irrigation are spelt out. Keywords: Surface water, Irrigation, Salinity, Sodicit