Glossary of Terms - Rainfall-Runoff Modelling: The Primer - page 384

Realisation effect The effect that short periods of observations or stochastic model outputs might lead
to different inferences when different periods or different realisations from the stochastic model are
used [Section 8.7]
Real-Time Forecasting and Updating Operational forecasting of flows during an event, usually
to predict the possibility of flooding, often with adaptive updating of model parameters based
on the errors between observed and predicted variables (see also Lead Time) [Sections 4.8, 8.4;
Box 8.1]
Regionalisation The process of estimating the response of an ungauged catchment using information
transferred from gauged catchments [Chapter 10]
Relaxation time The time scale over which the impact of a particular event can be distinguished
[Section 9.7]
Residence Time Distributions The distribution of times that particles have been within a hillslope,
channel network or catchment system. There are at least three different uses: to indicate the distribution
of times that it takes an increment of input to get to the outlet; to indicate the distribution of times it has
taken for the water in an increment of discharge to arrive at the outlet; and to indicate the distribution
of times that water has been stored in the system at any given moment. These are all different and
should be differentiated (see also Travel Time Distributions) [Section 11.8-11.10]
Response Surface The surface defined by the values of an objective function (or other model output
variable) as it changes with changes in parameter values. May be thought of conceptually as a surface
with “peaks” and “troughs” in the multidimensional space defined by the parameter dimensions, where
the peaks represent good fits to the observations and the troughs represent poor fits to the observations
(see also Parameter Space) [Sections 1.8, 7.2]
Riparian Area The part of the catchment that is immediately adjacent to the stream and is often the
most important source of runoff, both surface and subsurface [Section 1.4]
Runoff see Overland Flow, Storm Runoff, Surface Runoff, Subsurface Stormflow.
Runoff Coefficient The proportion of the rainfall volume in a storm that appears in the storm hy-
drograph. The value will depend on how the storm runoff component of the hydrograph is defined
[Section 2.2]
Runoff Generation The process mechanisms that contribute water to the hydrograph in a channel for
a rainfall or snowmelt event. May include both surface and subsurface processes. May also include
contributions from both the event inputs and displacement of pre-event stored water.
Runoff Routing The translation of surface runoff and subsurface stormflow to a point of interest, usually
the catchment outlet, taking account of surface, subsurface and channel flow velocities [Sections 1.6,
4.4, 5.5, 5.6, 6.1]
Saturation Excess Runoff generated by rainfall onto saturated soil, even though the rainfall intensity
may not exceed the normal infiltration capacity of the soil. May be used either at the local point scale
within a catchment (when the surface runoff may infiltrate further downslope) or at the catchment
scale to represent that part of the storm hydrograph generated by a saturation excess mechanism
[Section 1.4]
Similar Media A method of scaling the soil moisture characteristics of heterogeneous soils by making
assumptions about the structure of the media (e.g. that the geometry of the soil matrix is identical,
different only in length scale between different samples) [Box 5.4]
Slope-AreaMethod Method of measuring a peak discharge after a flood event using one of the uniform
flow equations by estimating the cross-sectional area, water surface slope and roughness coefficient at
a site [Section 3.2]
Snow Course Transect where regular measurements of snow depth and density are made [Section 3.1]
Soil Moisture Deficit (SMD) A state variable used in many hydrological models as an expression of
soil water storage. SMD is zero when the soil is at field capacity and gets larger as the soil dries out.
It is usually expressed in units of depth of water [Sections 1.4, 3.1]