Data
Field in Data Entry Form | Description | Namein Datafile | Default value | Constraints |
|---|---|---|---|---|
Time step | Time interval used in unit hydrograph and rainfall profile (hrs). | ∆t | - | >0 |
α Factor Method | aT calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the aT value is calculated by Flood Modeller by interpolating for the given return period from a lookup table of aT values against return periods for the given season. Note that the season is obtained from the value set by SEASONFLAG. If set to 'USER', the input value of aT is used. | ALPHAFLAG | DESIGN |
|
α Factor | Initial soil moisture correction factor. (only used if ALPHAFLAG is set to 'USER'). | ALPHA (aT) | 1 | 0 < aT ≤ 1 if ALPHAFLAG='USER' |
ARF | Areal reduction factor to relate point rainfall to areal rainfall. Range 0.0 to 1.0. The input value of arf is ignored and calculated internally if ARFFLAG is set to 'DESIGN'. | arf | - | 0 < arf ≤ 1 if ARFFLAG='USER' |
Areal Reduction Factor Method | ARF calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the areal reduction factor is calculated by Flood Modeller as a function of STAREA and STDUR from a digitised form of Figure 3.4 in the FEH Volume 4. If STAREA is set to zero then CAREA is used. If set to 'USER', the input value of arf is used. | ARFFLAG | DESIGN |
|
BF0 | Initial Baseflow (m3/s). The input value of BF0 is ignored and calculated internally if BF0FLAG is set to 'DESIGN'. | BF0 | 0 | >0 if BF0FLAG='USER' |
BF0 Calculation Method | Baseflow calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the initial baseflow is calculated by Flood Modeller as a function of CINI, SAAR and [catchment] AREA. If set to 'USER', the input value of BF0 is used. | BF0FLAG | DESIGN |
|
BFIHOST | Baseflow index catchment descriptor | BFIHOST | - |
|
Simulation Type | Flow values to use during simulation, can be one of: 'base flow ('bfonly') 'peak flow' ('pfonly') 'full hydrograph' (null, default) For example, if 'base flow' is selected then the baseflow contribution is used for the boundary flow value for the simulation. | bfonly | <blank> |
|
BL | Baseflow lag (hrs, only used if BLFLAG is set to 'USER'). | BL |
| >0 if BLFLAG='USER' |
BL Donor Correction Factor | Baseflow lag donor correction [multiplicative] factor. | BLDCF | 1 | >0 |
BL method | Baseflow lag (BL) calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the BL is calculated by Flood Modeller as a function BFIHOST, PROPWET, URBEXT and DPLBAR. If set to 'USER', the input value of BL is used. A donor correction factor may also be applied to the calculated value of BL. | BLFLAG | DESIGN |
|
BR Method | Baseflow recharge (only used if BRFLAG is set to 'USER'). | BR |
| >0 if BRFLAG='USER' |
BR Donor Correction Factor | Baseflow recharge donor correction [multiplicative] factor. | BRDCF | 1 | >0 |
BR Calculation Method | Baseflow recharge (BR) calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the BR is calculated by Flood Modeller as a function BFIHOST and PROPWET. If set to 'USER', the input value of BR is used. A donor correction factor may also be applied to the calculated value of BR. | BRFLAG | DESIGN |
|
c | Catchment descriptor - DDF model parameter c. | c | - |
|
Calibration Factor | Calibration factor applied to each sub-hydrograph 1: unpaved 2: urban, drain away; 3: urban, drain towards | calib(i) | 1 | Real. >0 |
Area | Contributing catchment area (km2) | CAREA | - | >0; warning if area < 0.038 or area > 9868 |
Cini | Initial soil moisture content (mm, only used if CINIFLAG is set to 'USER'). | CINI |
| >0 if CINIFLAG='USER' |
Cini Method | CINI calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the CINI value is calculated by Flood Modeller as a function CMAX, BFIHOST and PROPWET for the current season (defined by SEASONFLAG). If set to 'USER', the input value of CINI is used. | CINIFLAG | DESIGN |
|
Cmax | Maximum soil moisture capacity (mm, only used if CMAXFLAG is set to 'USER'). | CMAX |
| >0 if CMAXFLAG='USER' |
Cmax Method | CMAX calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the CMAX value is calculated by Flood Modeller as a function BFIHOST and PROPWET. If set to 'USER', the input value of CMAX is used. A donor correction factor may also be applied to the calculated value of CMAX. | CMAXFLAG | DESIGN |
|
Cmax Donor Correction Factor | CMAX donor correction [multiplicative] factor. | CMDCF | 1 | >0 |
d1 | Catchment descriptor - DDF model parameter d1. | d1 | - |
|
d2 | Catchment descriptor - DDF model parameter d2. | d2 | - |
|
d3 | Catchment descriptor - DDF model parameter d3. | d3 | - |
|
DPLBAR | Mean drainage path length catchment descriptor (km) | DPLBAR | - | >0 |
DPSBAR | Mean drainage path slope catchment descriptor (m/km) | DPSBAR | - | >0 |
e | Catchment descriptor - DDF model parameter e. | e | - |
|
Easting | Easting coordinate of catchment outflow (not used in calculations) | easting | 0 |
|
Rainfall Flag | Event rainfall calculation option Design Rainfall or Observed (ERFLAG='DESIGN' or 'USER'). If set to 'DESIGN' then the DDF model, SCF and ARF are combined to give a rainfall depth. If set to 'USER', the input value of precipitation is used. | ERFLAG | DESIGN | For METHOD='DLL', only 'DESIGN' is possible |
f | Catchment descriptor - DDF model parameter f. Only used if ERFLAG = 'USER', the remainder only if ERFLAG = 'DESIGN'. | f | - |
|
Boundary Type Flag | Boundary mode flag: 'HYDROGRAPH' denotes a generated hydrograph (i.e. the unit behaves as a QTBDY); 'HYETOGRAPH' indicates that it behaves as a REBDY-type unit, applying the Rainfall profile to a Rainfall-Only boundary (the latter must be used in conjunction with lateral inflow unit) | hymode | HYDROGRAPH |
|
Node Label | Node label identifier | Label | - |
|
Loss to sewers | Determines whether urban sewer loss is by volume or flow rate. | Loss_by | 'VOLUME' | 'VOLUME' or 'FLOW' |
Calculation Source Flag | Calculation method - determines whether the WHS dll ('DLL') or the 'hardcoded' method from the published report ('REPORT') is used for calculations. | METHOD | 'DLL' | 'DLL' or 'REPORT' |
Minimum Flow | Minimum flow (m3/s). Usually zero. Forces the resultant hydrograph to be not less than the specified flow. This may be required for program stability | minflow | 0 | ≥0 |
Northing | Northing coordinate of catchment outflow (not used in calculations) | northing | 0 |
|
n/a | Number of rainfall profile values | nrp | 0 | >0 if RPFLAG='USER' |
n/a | Number of unit hydrograph ordinates. May equal zero if UHFLAG = 'DESIGN'. | nuh | 0 | >0 if UHFLAG='USER' |
Observed Rainfall Depth | Event rainfall precipitation (mm). This is deemed to include any seasonal or areal correction factors. Only used if ERFLAG is set to 'USER'. | P | 0 | >0 if ERFLAG='USER' |
PROPWET | Catchment descriptor - proportion of time catchment soil moisture deficit (SMD) was below 6mm during the period 1961-1990. (range 0.0 - 1.0) | PROPWET | - | 0 ≤ PROPWET≤ 1 |
Observed Rainfall: Rainfall | Rainfall profile starting at tstart with data interval t (mm) | rp | - | ≥ 0 if RPFLAG='USER'; Σrp=P |
Sewer Capacity | Return period (yr) or depth (mm) value used in calculating drainage capacity of sewers draining away from the watercourse | RPDvalue | 10 | Real. ≥0 (depth) >2 (return period) |
n/a | Rainfall profile option ('DESIGN' or 'USER'). If set to 'DESIGN', then the standard rainfall profile for the current season (50% summer or 75% winter) is used. If set to 'USER', the input values of the rainfall profiles are used. | RPFLAG | 'DESIGN' | For METHOD='DLL', only 'DESIGN' is possible. Value written automatically by the UI, dependent on ERFLAG |
Use refined rainfall profile | If checked (refine rp=1), uses a finer discretisation of the standard FSR rainfall profiles - can prevent 'blocky' rainfall profiles for long storm/short data interval events | refine_rp | 1 | 0 to 1 |
Sewer Capacity: Flag/Value | [Urban ReFH] Flag to denote whether return period (rpordepth='RETURN') or depth (rpordepth=‘DEPTH’) is being used in calculating drainage capacity of sewers draining away from the watercourse. The value entered is either the return period (yr) or rainfall depth equivalent (mm). | RPorDEPTH, RPDvalue | ‘RETURN’ | ‘RETURN’ or ‘DEPTH’ only |
Season Flag | Season flag - 'SUMMER', 'WINTER' or 'DEFAULT'. If set to 'DEFAULT', then WINTER applies if URBEXT<0.125; SUMMER otherwise. Uses the design rainfall profile (50% summer or 75% winter), SCF, CINI, aT and BF0 values for the season, where appropriate. 75% winter and 50% summer profiles are taken from Figure 3.5 in FEH Volume 4 | SEASONFLAG | DEFAULT |
|
SAAR | Standard annual average rainfall (mm) - catchment descriptor. | SAAR | - | >0 |
Hydrograph Scaling Method: Scale | Hydrograph scaling method FULL (scaling = 'FULL': default) scales the whole hydrograph; Quick Runoff (scaling='RUNOFF'): scaling only applies to the quick runoff component of the hydrograph.. Used in conjunction with SCFLAG and scfact. | SCALING | 'FULL' |
|
method | Hydrograph scaling option. By a factor of (’scflag='SCALE' [default]) – applies the specified factor; To fit peak of (scflag='PEAK') – fits the hydrogrpah peak to the specified value. | SCFLAG | 1 | >0 |
| If SCFLAG='PEAK' then all hydrograph ordinates are scaled (by a constant value) to achieve a peak flow of scfact. If SCFLAG='SCALE' then all hydrograph ordinates are multiplied by scfact (default is 1.0). | scfact |
|
|
Seasonal Correction Factor (SCF) | Seasonal correction factor applied to the DDF rainfall (along with ARF) to derive the design rainfall (only used if SCFFLAG is set to 'USER'). | SCF | 1 | >0 if SCFFLAG='USER' |
Seasonal Correction Factor Flag | SCF calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the SCF is calculated by Flood Modeller as a function SAAR and the storm duration for the current season (as given by SEASONFLAG). If set to 'USER', the input value of SCF is used. | SCFFLAG | DESIGN |
|
Snow Melt Rate | Rate of snowmelt (mm/day). Not used (yet) in ReFH. | SNRATE | 0 | ≥0 |
Storm Area | Storm area (km2). This is used only in calculating ARF (and has no effect on the rainfall volume); if STAREA is entered as zero or negative then STAREA is set to CAREA | STAREA | 0 | For METHOD='DLL', this is not active |
Storm Duration | Storm duration (hrs). Should be the nearest odd integer multiple of ∆t. | STDUR | - | >∆t |
Area for subarea | Subcatchment area (km2) for subareas: 1: unpaved; 2: urban, drain away; 3: urban, drain towards | SUBAREA(i) | 0? | Real. ≥0 |
DPLBAR for subarea | DPLBAR (mean drainage path length, km) value for subareas: 1: unpaved; 2: urban, drain away; 3: urban, drain towards | SUBDPLBAR(i) | 0 | Real. ≥0 |
BR (for subarea) | Baseflow recharge parameter for subareas: 1: unpaved; 2: urban, drain away; 3: urban, drain towards | subbr(i) | - | Real. ≥0 |
Percentage Runoff value for subarea | Percentage value for subareas: 2: urban, drain away; 3: urban, drain towards | subpr(i) | 70 | Real. 0<subpr≤100 NB There is no subpr(1) |
URBEXT1990 for subarea | URBEXT1990 value for subareas: 1: unpaved; 2: urban, drain away; 3: urban, drain towards | SUBURBEXT(i) | (0, 0.5, 0.5) | Real. [0,1]. |
Return Period | Return period (years) | T | - | >1; warning if T>150 |
Time Delay | Optional delay time (hrs), e.g. if tdelay=2hrs then the hydrograph will start 2hrs after the start time of the simulation. | tdelay | 0 |
|
Tp | Time to peak of instantaneous unit hydrograph (hrs) | Tp0 | - | >0 if TPFLAG='USER' |
TP donor correction factor | TP donor correction [multiplicative] factor. | TPDCF | 1 | >0 |
Tp method | Unit hydrograph Tp option ('DESIGN' or 'USER'). If set to 'DESIGN', Tp is calculated using catchment descriptors; if set to 'USER', the user input value of Tp is used. | TPFLAG | DESIGN |
|
| Time to peak of t-hour unit hydrograph (hrs) - not currently used | TpT | - |
|
n/a
| Unit hydrograph ordinates with data interval Dt (see units); only used if UHFLAG is set to 'USER'. (Not accessible from the user interface). | uh | - | ≥0 if UHFLAG='USER' |
n/a | Scaling factor for the unit hydrograph ordinates. Only used if the 'units' keyword is not recognised. If zero or blank then units of m3/s/mm are used. (Not accessible from the user interface.) | uhfctr | 0 |
|
n/a | Unit hydrograph option ('DESIGN' or 'USER'). If set to 'DESIGN' then the ReFH design 'kinked-triangle' unit hydrograph is used, using TP, Uc and UP. If set to 'USER', the input values of the unit hydrograph are used.(Not accessible from the user interface). | UHFLAG | DESIGN |
|
Uk | Dimensionless instantaneous unit hydrograph 'kink' facto the multiplier applied to UC, the triangular UH ordinate at time 2TP. NB If Uk = 1, then a triangular unit hydrograph results. Only used if UKFLAG is set to 'USER'. | Uk | 0.8 | >0 if UKFLAG='USER'; also cannot allow UH time base to be < 2Tp |
Uk Method | Uk calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the standard factor of 0.8 is used. If set to 'USER', the user input values of Uk is used. | UKFLAG | DESIGN |
|
Units | Units of the unit hydrograph ordinates. Keyword can be one of:
NB The conventional units often used are m3/s /cm/100km2 (Not accessible from the user interface) | units | 'mmarea' |
|
Up | Dimensionless instantaneous unit hydrograph ordinate at time to peak. Only used if UPFLAG is set to 'USER'. | UP | 0.65 | <2 if UPFLAG='USER' |
Up Method | UP calculation option ('DESIGN' or 'USER'). If set to 'DESIGN' then the standard value of 0.65 is used. If set to 'USER', the user input values of UP is used. | UPFLAG | DESIGN |
|
Use Urban subdivisions | Flag to denote if Urban ReFH variation is being used (Urban=‘URBANREFH’ if true) | Urban | <blank> | Blank, or ‘URBANREFH’. NB Any other value is interpreted as blank |
URBEXT | Extent of urban/suburban land cover (range 0.0 - 1.0) - catchment descriptor. NB The value of URBEXT affects the default season, i.e. if SEASONFLAG is set to 'DEFAULT', i.e. summer applies if URBEXT ≥ 0.125; winter otherwise. | URBEXT | - | 0 ≤ URBEXT ≤ 1 |
n/a | Elevation (mAD). Not used in ReFH calculations. | z | 0 |
|
Theory and Guidance
Overview
The ReFH Urban is an enhancement of the existing ReFH rainfall-runoff technique in order to better estimate design flows in heavily or very heavily urbanised catchments. This alternative method which is based on the study published by Kjeldsen (2009, revised 2013) can be applied when there is a difference between the boundaries of the topographic and sewer catchments.
Methodology
The steps involved in applying this method are described as follows:
1. Division of catchment
This is done by splitting up the catchment into four sub-catchments, namely:
- unpaved sub-catchments;
- paved sub-catchments where topography drains into the watercourse but the sewers drain out of the catchment;
- paved sub-catchments where both the topography and sewers drain towards the watercourse;
- paved sub-catchments where sewers drain towards the watercourse from outside the topographic catchment – a less frequent occurrence. The flows in this case can be represented in the model by using a different technique rather than ReFH unit (eg a Flow-Time Series Boundary - QTBDY etc).
Figure. Example of catchment sub-division (Environment Agency, 2012)ReFH performance is adjusted for each sub-catchment type to reflect behaviour. The following FEH catchment descriptors should be adjusted for each sub-catchment:
- Area
- DPLBAR – Index of catchment size and drainage path configuration (km)
- URBEXT1990 – proportion of urbanisation as of 1990
Additionally, a value for BR (Baseflow Recharge) is required to be entered for each sub-catchment. Note: If this is omitted or zero, a whole-catchment value, calculated from BFIHOST and PROPWET, will be used.
2. Computation of flows for unpaved sub-catchments
The standard ReFH method is used to calculate the individual flows for each rural sub-catchment. On the other hand, it is assumed that 60% of each urban sub-catchment are unpaved and behaves in a similar way as the rural catchments, thus, the same method (i.e. standard ReFH) is also applied. URBEXT1990 values are set to 0, resulting in a longer lag time.
The following example on how to calculate unpaved areas can be given: unpaved catchment includes the rural and unpaved urban components (such as gardens etc), therefore if a catchment is 80% rural and 20% urban, then:
Example
92% of catchment area is unpaved (=80%rural+60% of 20%urban)
8% is paved (=40% of 20%urban).
The values of 92% and 8% are the values, which have to be specified in the software interface.
In this example it is assumed that there are no sewers draining out, which is a third type of sub-areas in addition to paved and unpaved listed above.
3. Computation of flows for the paved areas of developed catchment (sewers drain away)
It is assumed that all storm water for return periods up to 10 years is captured by the drainage system and carried out of the catchment (no flow). The 10 years is a default value which can be changed by the user. For longer return periods, the 10-year event hyetograph is subtracted from the design rainfall before flows are calculated. The model percentage runoff (PR) is set to 70% and the URBEXT1990 value to 0.5, representing runoff over a paved area. This results in a shorter lag time as compared to that of the “unpaved sub-catchments”.
4. Computation of flows for the paved areas of developed catchment (sewers drain towards the watercourse)
It is assumed that all water falling on the catchment will be drained towards the watercourse (either through the sewer lines or topographic routes). Hence, the method is done similarly to that of step 3; however, no reduction of the hyetograph is performed. The model percentage runoff (PR) is also set to 70% and the URBEXT1990 value to 0.5, representing runoff over a paved area.
5. Urban baseflow
Following further research by Kjeldsen et al. (2013), it was noted that applying the catchment-wide baseflow model to the sub-catchments often resulted in unrealistically large estimations of baseflow in the urbanised regions. It was suggested that the recharge be related to the direct runoff in the rural sub-catchment alone. Furthermore, a separate value of the baseflow recharge parameter (BR) is required for each sub-catchment. Note: the changes in this paragraph apply from version 4.0 onwards.
6. Addition of hydrographs
The ReFH is run for each sub-catchment separately to generate the individual design flow hydrographs. Two hydrographs are produced for each sub-catchment, representing unpaved and paved areas. Then, the resulting outputs are combined together to provide a total inflow hydrograph which can be used as an input to a hydraulic model.
Notes:
- The loss to sewers in the “Paved, sewers draining away” sub-catchment is calculated or specified as an equivalent event rainfall depth. When calculated from a given return period, the design rainfall depth is NOT seasonally corrected.
- The option to specify the above loss as a rate or a volume denotes whether the depth lost is:
- (by Rate): averaged across the storm duration and any excess from the actual rainfall is considered as quick runoff. This simulates the situation where a sewer capacity is more influenced by a maximum flow rate.
- (by Volume): all considered as loss up to a time at which the cumulative rainfall exceeds the sewer loss equivalent; any rainfall from this time onward is considered as quick runoff. This simulates the situation where a sewer capacity is more influenced by a maximum storage.
- Baseflow Lag (BL) is not entered explicitly for each sub-catchment, but calculated from the (sub-)catchment parameters, including DPLBAR and URBEXT.
How to access the ReFH Urban Interface?
The ReFH Urban is incorporated within the ReFHBDY interface. Upon opening a ReFHBDY unit, the user is presented with the first tab named "Catchment" where an option to activate the ReFH Urban is located.
By ticking on the check box "Use Urban subdivisions" at the bottom part, the ReFH Urban interface is automatically added on the menu bar. This allows the user to enter the parameters (as described in the methodology section) needed to calculate the design flow using the Revised ReFH Rainfall-Runoff Method.
Datafile Format
Line 1 - Keyword 'ReFHBDY' (case insensitive) #REVISION#2
Line 2 - Label
Line 3 - z, easting, northing
Line 4 - tdelay, ∆t, bfonly, SCFLAG, scfact, hymode, SCALING, minflow
Line 5 - CAREA, SAAR, URBEXT, SEASONFLAG, METHOD, Urban
Line 5.1 - SUBAREA(1), DPLBAR(1), SUBURBEXT(1), calib(1)), <blank>, <blank>, <blank>, <blank>, subbr (1)
Line 5.2 - SUBAREA(2), DPLBAR(2), SUBURBEXT(2), calib(2), subpr(2), RPorDEPTH, RPDvalue, loss_by, subbr(2)
Line 5.3 - SUBAREA(3), DPLBAR(3), SUBURBEXT(3), calib(3), subpr(3)), <blank>, <blank>, <blank>, subbr (3)
Line 6 - STAREA, STDUR, SNRATE
Line 7 - ERFLAG, ARFFLAG, comment
Line 8 - P, T, arf, c, d1 ,d2 ,d3 ,e ,f
Line 9 - RPFLAG, SCFFLAG, SCF
Line 10 - nrp
Line 10.1 to Line 17.nrp - rp
Line 11 - CMAXFLAG, CINIFLAG, ALPHAFLAG, comment
Line 12 - CMDCF, CMAX, CINI, ALPHA, BFIHOST
Line 13 - UHFLAG, TPFLAG, UPFLAG, UKFLAG
Line 14 - TPDCF, Tp0, TpT, DPLBAR, DPSBAR, PROPWET, Up, Uk
Line 15 - nuh, units, uhfctr
Line 15.1 to Line 15.nuh - uh
Line 16 - BLFLAG, BRFLAG, BF0FLAG
Line 17 - BLDCF, BL, BRDCF, BR, BF0
Notes: Line 5.1 to 5.3 only read if Urban = “URBANREFH”