Hydraulický výpočet pro drenážní systém

Metoda je založena dle (SNiP 2.04.03-85)

Hydraulický výpočet pro systémy odvodnění vody se provádí zvlášť pro každý pozemek a každou plochu samostatně. Nejlepší způsob je svěřit tento výpočet odborníkům, kteří se profesně zabývají projektováním drenáží a kanalizace.

Při projektování drenážních systémů a povrchových odvodňovacích kanálů je třeba vzít v úvahu řadu faktorů: úhrn srážek pro tuto oblast; parametry povrchu drenážních prvků; nominální drenážovaná plocha. Těmito parametry je určen nominální průtok vody v l / s . Výběr vhodného žlabu se provádí na základě výpočtu její odtokové kapacity, což závisí na úhlu vedení drenáže a množství výstupů do systému odvodu dešťové vody.

In order to understand whether the selected channel could manage with water flow to be drained, it is necessary to calculate precipitation amount along the nominal area:

V=k x Q x S,

where,

k – drainage basin surface coefficient;

Q – precipitation rate for the given region in l/sec per ha (ha = 10 000 square meters);

S – nominal drain area in sq. m;

V – precipitation amount in l/sec for this region to be collected from the nominal area.

 

Example:

It is necessary to select a drainage channel. Surface type - macadam pavement, it means k = 0.25 (see table “Drain surface coefficient”, page 53);

City — Minsk, which means Q=80 l/sec per ha (see table “Precipitation rate”, page 53);

Area — S=L х E/10 000=20 х 20/10 000=0.04 ha (see scheme for nominal drain area)

If we apply the data available in the formula, we will obtain the amount of precipitation for this region which shall be collected from the nominal area:

 

V = 0.25 х 80 х 0.04 = 0.8 (l/sec)

 

At the next stage we determine which channel shall be applied, according to calculated V parameter a selection of drainage channel is made by means of catalogue following channel name. In our case channel 100.65 h65 is suitable, see table “Specifications of the channels”.

 

Specifications of the channels

№	load class	name	hydraulic calculation, mm	conveying capacity
1	А-Е	drainage channels 100.65 h65	DN 100	3,1
2	А-Е	drainage channels 100.95 h95	DN 100	4,2
3	А-Е	drainage channels 100.125 h125	DN 100	5,3
4	А-Е	drainage channels 100.175 h175	DN 100	8,1
5	А-Е	drainage channels 200.210 h210	DN 200	24,2

While matching system components it is of no less importance to select the correct grid to suit the chosen channel, which will correspond to declared load of the area where the systems are to be laid. Channels and grids shall always be selected in compliance with load class either for pedestrian area or place of cars and cargo carriers’ traffic.

 

The following factors shall be considered during hydraulic calculation:

1. Precipitation amount: information of Meteorological Offices on precipitation amount for each specific district can be found both in reference books, or by means of direct contacting to Meteorological Offices.

2. State of drainage systems being in operation: it shall be taken into the account that operated drainage systems are not always in a perfect state (inner section of the channels can be obstructed partially – leaves, rubbish, and etc.).

3. Location of drain line in unfavorable position or possibility of its sudden heavy pollution.

In order to ensure efficient and long operation of surface drain lines, it is necessary to:

1. Perform a correct hydraulic calculation and by means hereof select all elements of surface drain line system;

2. Carry out correct installation;

3. Ensure proper operation.

 

The amount of draining water, water level and bottom formation.

Bottom formation of the drainage channel, whether with slope or not, do not affect the amount of draining water. A water level line is always aligned in the same way. And the amount of draining water is always determined only with the help of cross-section of drainage channel, slope is irrelevant here.

Thus, it makes cost-saving possible, and moreover, makes the process of laying easier.

 

Data tables for hydraulic calculation

Precipitation rate
Russian regions	Q	Novosibirsk	60
Moscow	80	Krasnodar	70
Krasnodar	100	Irkutsk	70
Nizhny Novgorod	90	Vladivostok	100
Samara	70	Belarus regions	Q
Saratov	70	Minsk region	80
Saratov	60	Vitebsk region	90
Rostov on Don	90	Mogilev region	70
St-Petersburg	60	Gomel region	60
Kazan	80	Brest region	60
Perm	50	Grodno region	70

Drainage basin surface coefficient
Type of surface	Coefficient (k)
asphalt or concrete	0,95
paving stone with cement  compound	0,85
paving stone  with unisolated  compound	0,6
block with unisolated compound	0,45
road-metal cover	0,25-0,6
gravel cover	0,15-0,3
grass area depending of ground	0,05-0,35