Course Exercise: Management of the River Vidå

The course exercise is a case study of the river Vidå, which is located in the South of Denmark at the border to Germany in a region of salt marshes.

Please read the general description of this region and have look on Vidå Photo before you start to work on the case study.

Case study description

The Vidå river has been modeled in an earlier project using the DHI software product Mike11 for the time period of 1st August 1990 to 1st October 1990. The structures in use 1990 are defined in the original data set.

The HydroWeb exercise is a case study, based on this model. Of course this is a theoretical, academic study without any relation to the actual river management in this region.

The case study is based on the original model. We removed all structures and changed some of the data. The objective of the exercise is to adapt this basic model for specified new boundary conditions and requirements to propose a suitable river management model for the time period of 1st September to 1st October 1990.

System Overview

The Vidå river model has some characteristic locations for boundary conditions:

water level time series

discharge time series

constant discharge

pump station

Two pump stations have been considered in the given model by constant discharge boundary conditiona.
The other pump stations are not considered in the model.

Modeling Tasks

The modeling tasks are structured in three parts: model set-up, model optimization and model study.

1. Model Set-Up

First task is to adapt the given river model to a list of predefined model information:

• Sediment Accumulations:

  After the latest measurements of the Vidå River cross sections, minor morphology changes have been discovered in the main channel (VIDAA-NED and VIDAA-Mel) due to a sediment transport (siltation). Please modify the cross sections at specified chainages respectively by sand filling, which should result in an elevation of the channel bottom level as defined below:

  River name	chainage	elevation
  VIDAA-NED	103, 556 m	23 cm
  VIDAA-NED	2359, 2797 m	25 cm
  VIDAA-MEL	2968, 3252 m	20 cm
  VIDAA-MEL	3466, 3660 m	30 cm

• Discharge Boundary Data:

  Some discharge values (boundary conditions) have to be modified:

  River name	chainage	constant discharge
  LINDSKOV	1.0 m	Q= 0.60 m³/s for the whole period
  SONDERAA	0.0 m	Q= 0.65 m³/s for 1st Sep to 15th Sep Q= 0.95 m³/s for 16th Sep to 1st Oct

• Pumpstations:

  Hydrological events increased the amount of water in the drainage system of Højer Kog, Rudbøl Kog and Møgeltønder Kog area as well as Brunottenkoog and Hülltofter Tief on the German side. There is an urgent need to discharge the excessive drainage water from this polder area into the Vidå River during the modeling period by the existing pump stations at the end of the collecting channels. (see the map and photos).

  You should consider the following simplified conditions:

  1. The total amount of the water at each pumpestation to be released to the Vidå river during the 30 days is specified in column 3 of the table below.

  2. The ranges for the pumping rate at the stations to deliver the above amounts are given in column 4, 5 and 6 for three time windows of the simulation period.
     

  Name	Location	Water Volume 01.09. - 01.10.	Discharge m³/s 01.09. - 10.09.	Discharge m³/s 11.09. - 20.09.	Discharge m³/s 21.09. - 01.10.
  Schöpfwerk Verlath	VIDAA-RUD ch 0	7 500 000 m³	0.0/1.6/3.2/4.8/6.4	0.0/1.6/3.2	0.0/1.6/3.2/4.8/6.4
  Pumpestation Lægan / Møllehus Toldsted	VIDAA-MAG ch 53	12 000 000 m³	0.0/2.5/5.0/7.5	0.0/2.5/5.0	0.0/2.5/5.0/7.5
  Pumpestation Sejersbæk	SEJERSBK-NED ch 15	4 000 000 m³	0.0/1.6/3.2	0.0/1.6/3.2/4.8	0.0/1.6/3.2/4.8
  Pumpestation South of Højer	SEJERSBK-NED ch. 1710	4 500 000 m³	0.0/1.4/2.8/4.2	0.0/1.4/2.8	0.0/1.4/2.8/4.2/5.6
  Pumpestation Nørremølle / Rudbøl Kog	VIDAA-NED ch. 5117	11 500 000 m³	0.0/2.6/5.2	0.0/2.6/5.2/7.8	0.0/2.6/5.2/7.8

• Galgestrom Branch:

  The cross section file of the given model file sets contains data for the Galgestrom branch, located at the north east of Tønder. Please extend the model with the branch "GALGESTROM" with the TOPO ID "TOPO-96" for the first 2520 m. You have to edit new points and a new branch. Please specify upstream a boundary condition with the constant discharge of 0.2 m³/s and the downstream connection to VIDAA-OVR 3689.

2. Model Optimization

The given model is without any structures. Please optimize the model by suitable human inventions (broad crested weirs, dredging, dams etc.) to fit the general targets of the river model:

• Navigation: Maintain a minimum water depth (1.2 m) in the main river for navigation purposes, particularly between the North Sea and the junction in the river near Møllehus (Pumpestation) (VIDAA-MEL 1250)
• Flooding: Limit the maximum water level to protect against flooding in all branches for the defined period
• Tønder Park Lake: Maintain a predominant horizontal water level through the town of Tønder for amenity purposes (operation of fountain)

Please manage this river system with the given constraints and targets. You can add structures like broad crested weirs but not more than six in total. You could also carry out some limited dredging or to rise up the dikes and dams. However you should aim to have no flooding for the given simulation time period. The boats are small pleasure craft that need a depth of water of 1.2 m.

Take care to minimise velocities in the river to reduce sediment transport. Also, aim to use storage efficiently.

3. Model Study

Once you have derived your solution for the model optimization, do the following tasks:

• Time Step: Check the effect of using 30 min, 60 min and 90 min time steps in your model (rather than the 15 min time step you will probably have used for the tasks above).
• Bed Resistance: Find out how the performance of your model changes if the Manning-Strickler value M is (i) 20.0 for all sections, or (ii) 40.0 for all sections.
• Bridge Construction: The bridge at VIDAA-NED 5300 (nearby the Pumpestation) has to be reconstructed. The responsible construction company asks for a temporary reduction of the cross section width to 10 m for at least 14 days at the begin of September 1990 to check the bridge foundation. Please try to give a first (not final) answer to this question.

Discuss your findings.

Reporting

Each team should produce two reports at the end of the project:

• Engineering Report: The solution you have obtained to solve the engineering problems, with clear reasons for your choice, and a discussion of the effects of varying the time step and roughness.
• Collaboration Report: Your experiences on Web-based collaborative engineering in HydroWeb, particularly on how effective were the team work in distributed sub teams.

Model / Data Set

You can download the given starting model/data set of the exercise from the course web server.