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* Cross-fall, ''S<sub>c</sub>'' (also expressed as a fraction).
 
* Manning’s roughness coefficient, ''n''. Usually ''n'' = 0.017 for a conventional road surface. Other values are given in the following '''Table 1'''. (For more details, please see Section: 4.3; p.g.:4/1;, Table 1 of the guidance).
 
'''Table 1:''' Values of Manning's ''n''
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* The grating type (P, Q, R, S or T), or the size and angle of kerb inlet.
 
* The maximum allowable Flowflow Widthwidth (as shown below by ''B'' in m) against the kerb.
<br>[[File:Figures 1 2.jpg|850px|]]<br>
 
 
'''A) Use of Tables for determining the flow capacity of gullies and maximum spacings for gully gratings'''<br>
Equations given in Section 5 of the guidance are used for the calculation of the Spacing of Road Gullies. Design Tablestables have been compiled to present a quick design approach. Tables can be found in Annex C.
Annex C includes Designdesign Tablestables for the grating types: Types P, Q, R, S and T. The Design Tables C2-C6 in Annex C of the guidance (p.g: C/3-C/12), present the area that can be drained for an intermediate gully and a range of crossfall and gradient of flow widths. For the Designdesign Tablestables a rainfall intensity of 50mm/h and Manning’s ''n'' = 0.017 are considered.
 
For ease of access, the Tables C2-C6 (Type P-T) of Annex C, are replicated in the Spacing of Road Gullies file here [Excel File]. Please see, tabs: Type P, Type Q, Type R, Type S and Type T. The Excel file provides tables like the following examples and their corresponding graphs.
<br>[[File:Tables C2-C6 of Annex C.jpg|950px|]]<br>
 
<br>'''Note:''' a) ''Tables C2 to C6 are for intermediate gullies on a uniform gradient and are not strictly accurate for gradients which vary greatly over short distances.''
b)''The Excel tables also present the flow collection efficiency η of the grating in % (in brackets)''. <br>
 
Based on Tables and Equations (2), (3) and (4) of the guidance (p.g: 5/1) the Maximum spacings for gully grating can be calculated.
 
 
'''B) Calculation of Gully Spacings based on Equations'''
<br>Alternatively, the equations given in Sections 5 of the guidance can be used for the Spacing of Road Gullies, directly. The method requires the calculations of the Flow capacity of the kerb channel and Flow collection efficiency of the gully grating.
*As a first step, a gully grate type: P, Q, R, S or T should be selected. The selection of the grating Type will determine the design value ''G<sub>d</sub>'' (grating parameter) from '''Table 2'''. (For more details, please see Annex B of the guidance; p.g.: B/1.). ▼
 
▲*As a first step, a gully grate type: P, Q, R, S or T should be selected. The selection of the grating Type will determine the design value ''G<sub>d</sub>'' (grating parameter) from '''Table 2'''. (For more details, please see Annex B of the guidance; p.g.: B/1.).
 
'''Table 2:''' Determination of grating type ''G<sub>d</sub>''
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*Further, a Water Depth against the kerb ''H'' (m) range should be provided. (Please note: The depth range can be changed, but the following equations that are used to calculate the flow capacity are only valid up to the kerb height).
 
*With the above parameters, the calculations of i) The Flow width (''B'' in m), ii) the Cross-sectional area (''A<sub>f</sub>'' in m2), iii) Hydraulic radius (''R'' in m), iv) Flow rate (''Q'' in m3/s) and v) Flow collection efficiency (''ŋ'' (%)) based on the Equations 6-10 which are presented in Section 5 (p.g.:5/2) of the guidance can be completed.
 
*Finally, the resulting depth-discharge data can be used in the pit inlet curves.<br>
 
The Spacing of Road Gullies Excel file above includes a calculation tab which can be used for the completion of the calculation process. Based on calculations and Equations (11) and (12) of the guidance (p.g: 5/3) the Maximummaximum spacings for gully grating can be calculated.
 
'''Key assumption'''<br>'''Note:''' This method assumes that the route the flow takes around the trap limits the discharge from the gully pot to 10 l/s. This limit is effective in both directions, so any number of negative head on the gully would create -10 l/s flow back up through the gully and flood onto the road. <br>▼
'''Key assumption'''<br>
▲'''Note:''' This method assumes that the route the flow takes around the trap limits the discharge from the gully pot to 10 l/s. This limit is effective in both directions, so any number of negative head on the gully would create -10 l/s flow back up through the gully and flood onto the road. <br>
 
== How to Translate On-Grade Approach Flow / Pit Capture Flow Curves to Depth / Discharge Curves for use in TUFLOW ==
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