The Rainfall-Runoff Models

WaterWare includes two complementary rainfall-runoff models RRM, semi- and fully distributed:

• A semi-distributed model that connects any number of lumped but vertically distributed/corrected parameter (sub)basin model in a network topology; it provides direct input (inflow from start nodes of the type: catchment) to the water resources model;
• A fully distributed regular grid model based on high resolution DEM data, primarily designed for urban flooding problems.

Both models can receive their hydro-meteorological inputs (hourly or daily) from either monitoring station observation data, or from spatially distributed sources such as weather radar or prognostic numerical weather model results (WRF, MM5).

The RRM rainfall-runoff model can be explored in an interactive on-line demo

A semi-distributed multi-basin model
The rainfall runoff model (RMM) is daily, lumped parameter water budget and runoff model for networks of small and medium-sized sub catchments. It obtains its input data from the river basin objects and their associated time series of precipitation, temperature, and runoff data.

RRM is a daily, spatially aggregated water budget and runoff model for small and medium sized catchments, for which a representative synoptic rainfall can be defined.

The main functional elements and processes represented in the model are:

• Interception storage, which is a function of land cover; excess water reaches the soil (surface); from the interception storage, evaporation (function of temperature) is deducted;

• Soil surface; depending on infiltration capacity, (depending on land cover and soil moisture), precipitation is split into surface runoff (Hortonian flow) and infiltration.

• Depending on the air temperature (profile), which is calculated from the basins elevation distribution, precipitation can be both in the form of rain or snow. In the latter case, a snow pack is simulated, from which both evaporation and melting (the latter greatly enhanced by precipitation events above freezing) are estimated using a simple degree-day approach.

• Rootzone; this compartment represents the soil moisture in the rootzone, which is replenished up to field capacity; from it, evapotranspiration (a function of temperature, land cover, and soil moisture) returns water to the atmosphere; water in excess of field capacity reaches the next storage level, the

• Virtual drainage storage. From here water is split into an interflow component and (deep) percolation into the groundwater. Assuming a maximum speed of deep percolation, any excess water is routed through the soil system to the nearest channel as interflow.

• Groundwater system (shallow) supplies, in a non-linear function of storage, the baseflow contribution of the total runoff. Again a fraction of the (shallow) groundwater can percolate into a second, deeper layer that has no direct connection to the surface water system. From both shallow and deep groundwater, groundwater extractions (time series defined for specific wells or well fields) can be considered.

A fully distributed implementation

As an alternative to the semi-distributed representation, a fully distributed, grid based version of the dynamic model is also available.

Based on a high-resolution DEM (default: 30 m data from the global, public domain ASTER Global Digital Elevation Map, GDEM V2, 2011) it generates flow pathes and concentration areas automatically from the basin geometry, vegetation and soil data, evapotranspiration estimates, retention properties and local storage of every grid cell, and any explicit drainage network. Slopes and roughness together with the mass budget for each cell (excess water) determine the amount (and speed) of flow, connected the cells towards the basin outflow.

The model can reveive spatially distributed, dynamic input from numerical weather models or any other distributed source of hydro-meteorologiocal data, including spatially interpolated station data.

The model application for urban flooding is described in the on-line presentations :     Urban Flooding I     Urban Flooding II