Designing the “Chartak Ecotrail” in Uzbekistan is a part of “Medium-Size Cities Integrated Urban Development Project”, in short MSCIUDP funded by the World Bank Group.

The ecotrail for pedestrians and cyclists in situated along the river “Chartaksay”, and so the redesign of the river is one part of this project by “Superwien Architecture and Urbanism” beside the design of the paths and bridges and aspects of landscape, mobility, recreation and others.

Chartaksay River is characterized by very challenging hydrologic situation, which is caused by climate and irrigation. Most of the water in dry periods of the year is taken out of the Chartak Reservoir, so during the irrigation season there is a constant discharge of just 1 – 1.5 m³/s in the river. Mainly during the period when the reservoir is full (January-March), 4 – 6 m³/s of water from the river is transited. The Reservoir has also a diminishing effect on floods due to a volume of 10 Mio m³ for flood retention: Maximum discharge (emergency discharge) is 168 m³/s.

Basing on the topographic measurement we cut 16 cross-sections on a river length of 11,3 km to get a survey of the river by calculating a simple hydraulic1d-model. As a result we learned that on all of these 11,3 km there are no flood hazards for residential and industrial areas. Yet we calculated very high velocity (3-4 m/s!) and high shearing stress (140 N/m²) mainly in those parts that are regulated very narrow by concrete banks. In the other parts that are closer to nature velocities are lower with about 2 m/s and also shearing stress is lower (70-90 N/m²). The gradient of the river bed is constantly about 1 %.

Presently we can discern following zones:

• Regulated narrowed stream with concrete banks: width ~ 40 m, depth ~ 3 m
  km 0,0 – km 4,0, km 11,0 – Reservoir; partly concrete banks on just one side of the river; partly damaged by frost or erosion or material fatigue; partly banked up with dams up to 3 m high
• Zones close to nature: width up to 110 m, depth ~ 2 m, km 4,0 – 11,0 with several exceptions and partly concrete banks on one side; partly heavy shore fractures

We have developed 5 types of embankment:

Type I – Concrete paving = retaining the present situation
Because of high velocity and shearing stress, close-by residential areas, we recommend to retain the present concrete paving

Type II – Redesigning of shore fractures in hydraulic heavily strained ranges
In those parts where concrete paving is damaged or shore fractures have to be repaired because of hazards for residential or industrial areas we prefer to take Armorstones instead of concrete
Type III – Shore fractures without technical intervention
In parts where shore fractures will not hazard infrastructure or Industrial and residential areas shore fractures should not be redesigned because thy are important ecological habitats for birds and other fauna.
Type IV – Armoring the shore in slightly hydraulic strained ranges
Using Armorstones instead of concrete
Type V – Concrete paving with embankment stairs
Can be used in concrete armored shores to gather access to the river for people and animals