The following Input Variables are used in the FSR Unit Hydr= ograph:

This method may not be available for your region. For more information, ref=
er to the=20
Regionalisation=
topic.

**Area - **This is the catchment draina=
ge area.

**Areal Reduction Factor - **Reduces th=
e rainfall as it is calculated as point rainfall based on time and area. Th=
e value may be obtained from FEH Figure 4.3.4.

**Main Stream Length - **The length of =
the main stream (MSL) measured in metres on a 1:25000 Ordnance Survey Map. =
It is normally measured in kilometres (and represented in the formula=
e in km) but it is input into the software in metres to be consistent with =
other data input.

**H(85%) & H(10%) - **These values =
allow the main channel slope (S1085) to be calculated. The values are=
the heights at 10% and 85% of the main channel length upstream from the ca=
tchment outlet.

**SAAR - **Acquire the average annual rainfall value f=
or 1941 to 1970 from FSR Figure II.3.1 (Natural Environment Research Counci=
l, 1975). The data is also available from the Wallingford Procedure, =
Volume 3 Maps and the FEH CD. This can be determined by clicking on the 'Ma=
p' button and selecting the location.

**CWI - **The Catchment Wetness Index i=
s read off Figure I.6.62 in the FSR. The program will automatically c=
alculate this value based on the SAAR value entered above, but can be overr=
uled by entering the required value.

**Urban - **The fraction of each catchm=
ent given over to urban development =E2=80=93 the area coloured orange on a=
1:50000 ordinance survey map =E2=80=93 planning proposals can also be used=
for future estimates. Note this has been replaced by the digital dat=
a variable URBEX in FEH. URBANfsr =3D 2.05 URBEX. URBEX is avai=
lable from the FEH CD.

**SPR - **This value can be calculated =
from Figure I.4.18 (first revision) (Institute of Hydrology, 1978) which sh=
ows the various soil types. This can be determined by clicking on the 'Map'=
button and selecting the location. The soil classifications are also avail=
able from the Wallingford Procedure, Volume 3, Maps, =E2=80=9CWinter rain a=
cceptance potential=E2=80=9D. The equation was first published in FSS=
R 16, 1985.

** SPR=3D10S _{1} +30S2+37S_{3}+47S_{4}+53S_{5}**

where S_{1}-S_{2} are the proportions of the catchment c=
overed by soil classes 1-5 respectively.

Where measured flow records are available the SPR may be calculated from= the Base Flow Index (BFI) from research published in FSSR 16 and it is not= covered here =E2=80=93 see also FEH, Volume 4, Chapter 1.

**LAG - **This value can be used in lie=
u of S1085, Urban, SAAR and MSL to calculate the time to peak TP0. It=
is defined as the time delay between the centroid of a hyetograph and the =
resulting peak flow at the catchment outfall.

Note: This may be appropriate if measured lag values are available or if th=
e engineer estimates that the calculated time to peak is in error. Th=
is may be the case, for example, if the ditches have been improved or piped=
.

**Baseflow - **This value replaces the =
calculated baseflow value to allow a user defined baseflow. The basef=
low calculation can be switched off by entering a value of "0", it should b=
e left blank in order for the software to calculate it.