Subsequently, irrigation was developed as the need to channel the river's flow arose in order to sustain the crops and livestock. The ancient nomadic nature of man changed to a domesticated one: no longer was there a need to hunt for food. In these modern times, much headway has been made in harnessing the full potential of rivers. For instance, there is now a storage and systematic distribution of potable water from rivers through dams, reservoirs, pumps, and piping systems. Further, irrigation systems are now utilized to nourish plantations and livestock. The destructive nature of rivers in the form of floods is likewise much more minimized through the understanding man has gained in predicting their behaviour. The approach to understanding is both scientific and empirical and uses tools in recording and interpreting pertinent data from observations. This important tool is called the hydrograph. Hydrograph is defined as "..a time record of the discharge of a stream, river or watershed outleta hydrograph is a representation of how a watershed responds to rainfall."1 Hereunder is an example.
A storm hydrograph in particular "..shows the change in the water level from before to after the passage of the storm water through a given location."3 The factors that define the storm hydrograph basically depend on how the river reacts to rainfall. These factors can be summarized under the following: the characteristics of the river basin, the condition of meteorologic events, and land use. First, the characteristics of the basin refer to its physical attributes such as area, topography (in particular, drainage density directly proportionate to the number of tributaries), geometry, geology (of its underlying soil and bedrock), presence of vegetation, and its initial conditions. The trait that will cause a large runoff and a longer lag time (time interval from peak rainfall and peak river flow) is a large basin area while a short lag time can be expected for circular basins, steep slopes, less permeable soils and rocks, less vegetation and saturated underlying aquifers. The lag time is directly related to velocity of the water travelling thru the river: the faster the water travels, the quicker it will reach peak flow. Flash floods provides a case in this point. An actual regular occurrence is at Cvennes-Vivarais Region in Southern France which is venue of severe flash flood events. The river is characterised by steep slopes in the head tributaries of the Cvennes Mountains.4 Secondly, metereological events pertain to rainfall, weather, and tidal conditions. Short intense rainfall and extreme weather swings bring about rapid surface runoff, short lag times, and graphically correspond to a steep rising limb in the hydrograph. On the other hand, the effect of tides is to block or stifle the egress of flooding water leading to a gradual slope of the recession limb in the hydrograph, thus a longer period for the river to return to its base (normal) flow. Lastly, the type of land use directly affects hydrograph parameters. Urban areas are likely to be less permeable due to presence of concreted