A hydrological model for predicting runoff from different land use areas

The purpose of this article is to model the influence of land use on catchment runoff. The modeling is based on the subdivision of the catchment into smaller units by generation of the so-called 'hydrologically similar units" (HSU) or "patch types". HSUs aggregate areas of hydrologically similar behavior, e.g., land use, soil, slope and vegetation. Each HSU is represented using a cross-section called a "characteristic profile". For the calculation of the water balance of the characteristic profiles, a mathematical treatment of the key partitions of the hydrograph response was developed. The characteristic ptofile is the largest unit that can be handled mathematically still maintaining the idea of a hydrologically similar regime. An agricultural characteristic profile is a cross-section between two parallel open ditches or sub-surface drains. For forest areas the characteristic profile is called hillslope and the length of the hillslope can vary from few meters up to hundreds of meters. The total runoff from the characteristic profiles is an input to a channel network. In the present model, the channel processes are described using the geomorphologic instantaneous unit hydrograph (GIUH). The proposed hydrological model was tested in the Lestijoki catchment (1290 km2) located in western Finland. The catchment was subdivided into 25 characteristic profiles with parameters fixed to typical values measured in Finnish conditions. The model calibration was carried out for the GIUH parameters using measured every-day river flow. The coefficient of determination was 0.74 for a 2 -y calibration period, and 0.70 for a 3 -y testing period. The model represented well the extent of variable contributing areas, which was the main reason for the non-linear behavior of the catchment response.