This document discusses methods for estimating missing rainfall data, including simple arithmetic averaging if normal annual precipitation is within 10% between stations, and a normal ratio method if precipitation varies considerably. It also discusses consistency testing of rainfall records using a double mass curve technique to identify changes in rainfall regimes. Methods for determining mean precipitation over an area using Thiessen polygons and isohyetal mapping are presented. The relationship between rainfall intensity, duration and frequency is examined through intensity-duration-frequency and depth-duration curves. An example illustrates plotting a rainfall hyetograph and intensity-duration curve from mass curve data.