Bharalu Polder/Reserviour at Riverfront for Flood Management
During Monsoon with high Water level of the Brahmaputra, the Discharge from Bharalu is severely restricted and only operational with the help of Pumps. The Combination of Sluice Gates and Pumps effectively means that the Bharalu becomes a reservoir during that period. The flooding in Guwahati along the Bharalu is primarily due to the mismatch between the rate of Discharge through Pumping and the Actual rise in water.
Proposal in Brief
In this context, a reservoir/polder (a Dutch name for such a feature) in between the Bharalu and Brahmaputra is an option to mitigate the yearly floods due to the overflowing Bharalu.
As the water in Bharalu surges during heavy shower, the excess water over its danger level can be diverted to the Polder/Reservoir. The size and feature of this Polder can be such that by way of displacement, it can accommodate water equivalent to 4.0 Mtr rise in the Bharalu Channel (12.0 Km Length) .
The Polder/ reservoir can have the Pumps to evacuate the water at an optimum pace. It this manner, the Polder /Reservior can act as a Flood Management feature between the Bharalu and The Brahmaputra , that will regulate the collection and discharge of water without inundating the city during heavy rainfall and sudden surge in water level of the Bharalu. (refer Fig: 1,2,3)
Location of the Flood Management System
In between the rocky outcrops at Sukreshwar and the Kalipur hillock, a natural cove if formed over the yers that has minimum current and mosty dry during the winters. This sand bar was where some festivals like the Brahmaputra Beach Festival was held. The area is a hockey stick shaped cove, which is sheltered from the main current of the Brahmaputra and also wider than the width of the Brahmaputra at Pandu. (Fig 4)
The Riverfront Works in the Cove
BY CREATING AN EMBANKMENT FROM SUKRESWAR UPTO THE KALIPUR – KAMAKHYA HILLS, WE CAN CREATE SPACE FOR A POLDER- a kind of reservoir used in Netherland to draining out water form low lying areas). As the Channel width at Pandu is upto 1.1 to 1.2 Km, the available area before KALIPUR can be upto 300 to 400 meters wide for a Polder. The area before the Polder from Sukreshawar point can be used to CREATE SPACE for an ICONIC TOURIST PLACE ALONG THE RIVERFRONT. (refer Fig:5)
Complete Look – The Cove
Polder (Spillway) Works
By creating a Polder in between Bharalu channel and Brahmaputra River, the Flood management of Bharalu can be effectively done as the Polder/ Spillway/ Reservior will accommodate the surge of water from Bharalu during monsoons for a specific time period before pumping catches up. This will drastically reduce the flooding arising out of overflow of Bharalu. Also the pumping facility can be greatly improved . Besides, the embankment will also add to the beatification and use of the river front. A difference of 3.0 meter between the normal Polder water lvl and the danger mark of Bharalu shall be adequate for this type of arrangement. (refer Fig:7)
- If X = 2.0 meter increase in Bharalu water level above 51.0 elevation
- X = 2 x 12000 x 15 (Height x Length x Width of Bharalu)
- Hence X = 3,60,000 cu.m
- If Y = Capacity of Polder with increase in water level from 48.0 to 51.0
- Y =3 x 1200 x 200 (Height x Length x Width*)
- Hence Y = 7,20,000 cu.m
- *Width of Reservoir is considered as 200 mtrs wide (available space is nearly 300-400 Meters)
If , Assuming , water level increase rate of Bharalu is 2.0 Meter per 8 hour, then Polder Capacity = 16 hour without mechanical discharge. Considering a tapering off in the rise beyond 8 hours, the capacity could be 24 hrs or more also. Combined with a pumping system, this could be a long term sustainable flood management system.
Infrastructure- Bharalu Polder and Channel Works
Impovement of Baharalu Runoff Speed, Polder for Excess Water, Sluice Gates, Pumps and Improvement of Feeder Drains. (refer Fig:8 )
- Probable Cost of Embankment(2.0 KM)- 50 .0 Crore
- Probable Cost of Concrete Embankment (1.5)- 150.0 Crore
- Probabale Cost of Landscape (1.8 KM)- 25.0 Crore
- Polder/ Reserviour Works-50.0 Crore
- Mechanical Pumping / Gate Works-25.0 Crore
- Bharalu Back Channel Developement- 2 KM- 25.0 Crore
- Total Amount – 325.0 Crore
- Land Recalimed Area- Approx 200,000 SQM
- Actual Land Capitalised – 100,000 SQM (75 Bigha Approx)
- Land Capitalised Value – 375.0 Crore
Presentation of Concepts/Proposal for Guwhati to The Govt of Assam for Consideration.
This study is prepared by Mr Rittick Hazarika , practicing Architect from Guwahati. This a further development of a paper by himself, presented at CESDOC 2016 at AEC, Guwahati.