Experimental investigation of the effect of dual horizontal screens on the hydraulic performance of a vertical drop

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One of the most effective ways to dissipate the destructive energy of water downstream of a flow control structure is the interference of water with air (such as a vertical drop). In this study, the hydraulic parameters of a vertical drop equipped with dual horizontal screens and with the subcritical upstream flow were investigated. Experiments were performed for two drop heights, two porosities, three relative distances between the screens, and a relative critical depth that was varied from 0.077 to 0.242. The results revealed that the relative distance between the screens does not affect the relative depth and downstream residual energy. On the other hand, increasing the relative length of the drop caused a decrease in the relative depth. Also, for a vertical drop equipped with a type 1 settling basin, the relative downstream depth decreased by more than 48%. The normal residual downstream energy and the relative total length of the drop are also decreased. The results also reveal that the use of dual horizontal screens transformed the regime of flow from super- to subcritical downstream of the drop.

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S p :

distance between the screens (m)

P :

porosity of screens (dimensionless)

h :

drop height (m)

Q :

flow discharge (m3 s−1)

g :

gravitational acceleration (m s−2)

y c :

critical depth (m)

y u :

approach flow depth (m)

y d :

downstream depth of the drop(m)

y p :

back pool depth (m)

L wet :

wetted length of the screen (m)

L mix :

mixing length of pool (m)

E d :

specific energy of drop downstream (m)

E u :

total energy of drop upstream (m)

α :

relative critical depth (dimensionless)

S pr :

relative distance between screens (dimensionless)

Y p :

relative pool depth (dimensionless)

Y d :

relative downstream depth (dimensionless)

L w :

relative wetted length (dimensionless)

L m :

mixing length (dimensionless)

E d :

normalized residual energy (dimensionless)

Ψ :

relative reduction percentage pool depth (dimensionless)


pool depth for vertical drop equipped with double horizontal screens (m)

Y ps :

pool depth for vertical drop equipped with a single horizontal screen (m)

L d :

drop length (m)

L b :

length of the hydraulic jump (m)

L sm :

relative length of plain vertical drop (m)

ω :

ratio of increasing the relative downstream depth (dimensionless)

Yd d :

relative downstream depth of the plain vertical drop (m)

Yd s :

relative downstream depth of vertical drop equipped with double horizontal screens (m)


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The authors wish to thank all who assisted in conducting this work.

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Correspondence to R. Daneshfaraz.

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Editorial responsibility: M. Abbaspour.

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Daneshfaraz, R., Majedi Asl, M., Razmi, S. et al. Experimental investigation of the effect of dual horizontal screens on the hydraulic performance of a vertical drop. Int. J. Environ. Sci. Technol. (2020) doi:10.1007/s13762-019-02622-x

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  • Dual horizontal screens
  • Energy dissipation
  • Relative length of drop
  • Vertical drop