The study investigated the use of oil palm stem ash as partial replacement of OPC for sandcrete hollow block production which ranges from 0 to 25% (at 5% interval). Ninety six (96) sandcrete blocks were cast using 1:6 as mix ratio of cement: sand with 0.45 water cement ratio. The compressive strength, density, porosity and abrasion test were carried-out on sandcrete block were tested at curing age 7, 14, 21 and 28 days. The oil palm stem ash was analysed for chemical composition of (SiO2, Al2O3 and Fe2O3) in which the summation is 75.3%. it was observed that compressive strength and bulk density decreases as the content of OPSA increases but 5% of OPSA has value of 4.66N/mm2 and 2111.20Kg/m3 as against the control 5.12N/mm2 and 2162.01Kg/m3 respectively. The porosity and abrasion test revealed the increase in value as the percentage content of OPSA increased. It was concluded that OPSA is a good pozzolan having satisfied the required standard. which can be used as 10% of OPSA content insandcrete hollow block production having attained a 28 day compressive strength of more than 3.5N/mm2 as required by the Nigeria National Building Code (2007) for non load bearing wall.

The study aims to determine the runoff depth using Soil Conservation Service Curve Number (SCS-CN) method in Geographical Information System (GIS) environment. For River Asa Watershed, the SCS Curve Number method has been adopted for estimating the runoff depth using Rainfall data from 1987-2018. Land use and change cover map were used for the classification of soil type, in order to determine the Hydrological Soil Group (HSG) using ArcGIS. The runoff was estimated from the rainfall runoff equation. The Antecedent Moisture Condition (AMC), potential maximum retention(s) and initial abstraction were computed. Thematic maps such as Soil and Land Use / Land cover and have been used in conjunction with hydrological data for determining hydrological soil Group (HSG) and Curve Number (CN) for land used and change cover classes over the watershed. The values of Hydrological Soil Group, Curve Number and Annual runoff depth varied (6.28-914.22) km2, (65-100) and (16.50-144.89) × 106 m3. The study shows that the high runoff depth was observed in Hydrological soil group (HSG), when compared with curve number (CN), this is due to dense vegetation cover.

The hydrological regime is characterized by high variability of rainfall and runoff distribution. The hydrologist finds it difficult to make accurate prediction of water abstraction by various dams. Inspite that Osun is blessed with abundant water resources being one of the states that supplier water to resident in Osun state, water supply is made inadequate due to lack of schedule of water by facilities abstracting water from the river. In this study, the Rainfall-Runoff Relationship for Determination of Water Abstraction Potential of River Osun was investigated. The model developed was a linear regression approach considering effects of past rainfall on the runoff of the effluent streams. Forty (40) years rainfall data collected from 1974 – 2012 were used to estimate corresponding runoff using empirical approach. The rainfall were repressed against runoff and the corresponding runoff arrived at regression coefficient of 0.912 and 0.896 respectively. Generated runoff for River Osun were determined. The data could serve as a veritable hydrological input in the allocation of water for the dams abstracting water on the river. It is recommended that to find a lasting solution to the menacing frequent lack of water by dams abstracting water on River Osun.