Larsen, Torben

Vestergaard, Kristian

English

A numerical model has been used to show how dilution in smaller streams can be effected by unsteady hydraulic conditions caused by a storm sewage overflow

    Aalborg UniversitetStorm Sewage Dilution in Smaller StreamsLarsen, Torben; Vestergaard, KristianPublication date:1987Document VersionAccepted author manuscript, peer reviewed versionLink to publication from Aalborg UniversityCitation for published version (APA):Larsen, T., & Vestergaard, K. (1987). Storm Sewage Dilution in Smaller Streams.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: November 30, 2020I . LAUSANNE AIHR-CONGRESS - IAHR STORM SEWAGE DILUTION IN SMALLER STREAMS Kristian Vestergaard & Torben Larsen University of Aalborg Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark SUMMARY: A numerical model has been used to show how dilution in smaller streams can be affected by unsteady hydraulic conditions caused by a storm sewage overflow . 1987 The discharge from storm overf lows into smaller streams cause significant un-steady hydraulic phenomena, which can lead to an important influence on the transport and dilution of discharged matter. The storm overflow discharge will cause a deceleration of the basic flow and an upstream storage of water will occur. As long as this storage takes place a weaker dilution than predicted by a steady state assumption will be a reality. This phenomenon has been simulated with a one dimensional integrated hydraulic-transport/dispersion model. The model is based on the Saint-Venant equations and the one-dimensional transport/dispersion equation, which with standard sym-bols (ref. 1) can be written: Conservation of volume: Conservation of momentum: ~ at a ah + - (U·Q) + g·A(- - S ) + g·A·S - q ·u ax ax 0 f - i i Conservation of matter: a ac - (A· K ·-) + source ax X ax The model set-up and the most important data can be seen on Fig. 1. In Fig. 2 the difference between a steady state assumption and a dynamic simulation is shown just downstream the overflow. In Fig. 3 the simulated flow and contratibn are shown in two stations downstream the overflow, and it can be seen that the dilution is significant weaker than predicted by a steady state model. Fig. 3 also shows another important unsteady phenomenon. In agreement with the theory a marked difference in wave celerity occurs between the flow and the transport of matter. Conclusions: With this brief description it is shown that unsteady hydraulic phenomena caused by storm water overflows into a smaller stream can lead to a significant weaker dilution of discharged matter than predicted by a steady state assumption. Reference: J.A. CUnge, F.M. Holly & A. Verwey, Pitman 1980: Practical Aspects of Computational River Hydraulics. llsectQ ~~o ~~~~ 0 5 10 15 20 25 30 65 min. 5 ~ t ~ 25min. C"' Omg0?/1 2 3 ,,. 2m . , M "'40 m1'l • sec-1 So ;: 5 '10-4 0 500 1000 1500 2000 2500 3000 3500 0 s t S65min. Q :100 l/sec C =10mg0/l 0 ~ t s 65min. h:0.19m Fig. 1. Model set-up and the most important data. 1/sec a FLOW 300 200 100 \ \ \ \ \ ---- STEADY- STATE -..-UNSTEADY ~--------------------------0.+---<>--+--+---+----+---+---+--+--+---+---l--+----+----c~ 0 5 10 15 20 25 30 35 40 45 50 55 60 65 mtn CONCENTRATION 5 10 15 20 25 30 35 40 45 50 55 60 60 mtn. Fig. 2. Flow and oxygen concentration at st. 1 just downstream the over-flow. A complete mixing across the cross section is assumed . I/ sec a FLOW 300 ST 3 200 -------- ..... /, ------,., -----z-------------100 ,'/ ST. 2 0 0 5 10 15 20 25 30 35 45 45 50 55 60 65 min. mg0211 c CONCENTRATION s~ 10 ------------· ... ... ' .,,."'"' ' ' 5 ' ' // ,, .... _______ 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 min. Fig. 3. Flow and oxygen concentration at st. 2 and 3. The concentration is still lower than the steady-state prediction at st. 1. The figure also shows that between st. 2 and 3 the wave celerity for flow is about three times greater than the wave celerity for transport of matter. 

Storm Sewage Dilution in Smaller Streams

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Storm Sewage Dilution in Smaller Streams

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