or rainfall excess, can be modeled by a pre-reservoir (figure 6) giving the recharge as overflow. The pre-reservoir knows the following elements: a maximum storage (Sm) with unit length [L] an actual storage (Sa) with unit [L] a relative storage: Sr = Sa/Sm a maximum escape rate (Em) with units length/time [L/T]. It corresponds to the maximum rate of evaporation plus percolation and groundwater recharge, which will not take part in the runoff process (figure 5, 6) an actual escape rate: Ea = Sr·Em a storage deficiency: Sd = Sm + Ea − Sa The recharge during a unit time step (T2−T1=1) can be found from R = Rain − Sd The actual storage at the end of a unit time step is found as Sa2 = Sa1 + Rain − R − Ea, where Sa1 is the actual storage at the start of the time step. The Curve Number method (CN method) gives another way to calculate the recharge. The initial abstraction herein compares with Sm − Si, where Si is the initial value of Sa. Nash model The Nash model uses a series (cascade) of linear reservoirs in which each reservoir empties into the next until the runoff is obtained. For calibration, the model requires considerable research. Software Figures 3 and 4 were made with the RainOff program, designed to analyse rainfall and runoff using the non-linear reservoir model with a pre-reservoir. The program also contains an example of the hydrograph of an agricultural subsurface drainage system for which the value of A can be obtained from the system's characteristics. The SMART hydrological model includes agricultural subsurface drainage flow, in addition to soil and groundwater reservoirs, to simulate the flow path contributions to streamflow. Vflo is another software program for modeling runoff. Vflo uses radar rainfall and GIS data to generate physics-based, distributed runoff simulation. The WEAP (Water Evaluation And Planning) software platform models runoff and percolation from climate and land use data, using a choice of linear and non-linear reservoir models. The RS MINERVE software platform simulates the formation of free surface run-off flow and its propagation in rivers or channels. The software is based on object-oriented programming and allows hydrologic and hydraulic modeling according to a semi-distributed conceptual scheme with different rainfall-runoff model such as HBV, GR4J, SAC-SMA or SOCONT. References Drainage Hydrology Hydrology models Water management Land management Scientific models Simulation software Scientific simulation software