Drainage Plan of Nabiganj Pourashava

This section of Nabiganj Master Plan states about goals and objectives, and methodology of Drainage Development Plan of this Pourashava area. An inventory of the existing drainage system of has been made as a part of the comprehensive topographical survey to be taken-up under this project. While assessing the drainage conditions, the serviceability, structural conditions, obstruction, siltation, blockages are taken into consideration. And finally describe the drainage and environmental management plan, and its implementation strategies.

Goals and Objectives

Provision of drainage facilities are important concern to human settlements to create better living environment. Failure to provide the adequate drainage facilities results in flooding and detrimental environmental quality. Drainage of high rainfall region particularly in the context of Sylhet region is very important.

The objectives of drainage planning are described as follows:

• To analyze drainage aspects in the planning of the Nabiganj Pourashava.
• To study geological fault and lineament of the project area and its surroundings.
• To study the existing water development, flood protection and flood control project (if any) in the area and their impacts in the Pourashava plan.
• To present planning options for drainage of the future Pourashava area.
• To study conservation of the natural resources like parks, open space, water bodies, existing ponds etc.
• To conserve place of historical, architectural (if any) and agricultural importance including natural fisheries.

Methodology and Approach to Planning

Drainage Network Survey for Pourashava has been carried out through the guideline of ToR of Upazila Towns Infrastructure Development Project (UTIDP) .In this survey explore the existing drainage network system at Nabiganj Pourashava. The main vision of this survey is explored the length, depth, flow direction, coverage area and satisfactory level of the Pourashava inhabitants. The information of drainage network gathered from topographic, socio-economic and physical feature survey (detail was given in Chapter 6, Section 6.2 of Survey Report of this Pourshava). Major feature of drainage and environment survey are as follow:

• Survey the main drainage channels from their heads to the outfalls and to estimate their capacity to discharge water.
• Collect and analyze meteorological data over time in the area to determine the meteorological conditions and predict storm surges.
• Determine the efficiency of the present drainage systems and make recommendation to government.
• Organize a public enlightenment campaign to expose the adverse effects of dumping refuse in drainage channels, through a mass media meeting.
• Drainage channels were surveyed by leveling from the head of the channels to the outfall using a surveyor's level. A zero datum was chosen at the head of each channel. This zero height was then used to level the channel from the head to the toe or outfall. In areas where water flow was observed, the velocity of the flow was recorded. The flow velocity was calculated by timing the flow rate within a 3-5m length of channel. In areas where sediment or refuse was observed to accumulate in the bottom of the channel, the thickness of such sediment or refuse was measured.
• A questionnaire was administered to local residents to collect information about flooding, refuse disposal and drainage channel patterns from local residents along flood prone areas. The answers to the questionnaire were statistically analyzed and use to decipher resident's opinion on the problem of flooding.

Existing Drainage System/ Network 

Man-made drains

Pourashava has only 8.20 Km drainage network at Nabiganj Pourashava area. Of these 0.20 km is Katcha drain and 8.18 km pucca drain. Table 6.4 shows inventory of major drain in Nabiganj Pourashava.

Natural Canal and River

General Description of Natural Canals

The existing natural canal network is remaining under haphazard condition in the total Pourashava area. In some portion of the area the condition of the khal and irrigation canal is being encroached by the local people and the situation is deteriorating day by day. So, it should be given much concern to sustain the natural canal.   

River

Shakhaborak River passes southern portion of the project area. It has been observed from the physical features survey that about 6.21 km of rivers and khals are passing through the project area. Table 6.5 shows ward wise length and area of Khal and river of Nabiganj Pourashava.

Beel/ Marsh land, Pond-Deghee, Ditch and Dyke

Apart from the natural drainage system, large number of ponds and ditches (686) are also observed in the area covering an area of 52.71 acres. Table 1 shows the detail.

Table 1: Ward wise Water Bodies in Pourashava

Ward no.	Pond, Ditch and Marshland
	No.	%	Area (Acres)
Ward-01	73	10.80	0.96
Ward-02	55	8.14	0.42
Ward-03	16	2.37	0.15
Ward-04	134	19.82	0.68
Ward-05	70	10.36	0.63
Ward-06	113	16.72	0.43
Ward-07	39	5.77	8.74
Ward-08	63	9.32	0.26
Ward-09	113	16.72	0.52
Total	676	100	12.78

Source: Physical Feature Survey, 2010

Analysis on land level Topographic contour

Total spot number was taken at Nabiganj Pourashava is 5766. Maximum height of Pourashava area is 10.20 mPWD and the lowest height is 4.20 mPWD and average height of the area is 7.03 mPWD. The highest percent area of Pourashava was found in contour 6.01-7.00 (mPWD) level (21.37%). Again as per this study it shows that more than 70% area of the town has 7 to 9  mPWD height.These areas are not free from normal flooding.  

Table 2: Percent Distribution of Spot Level according the Defined Height Interval (excluding River)

Spot Interval mPWD	Spot Number (Frequency)	Percentage
Up to 4.00	04	0.07
4.01-5.00	05	0.09
5.01-6.00	389	6.75
6.01-7.00	1232	21.37
7.01-8.00	3247	56.31
8.01-9.00	817	14.17
9.01-10.00	66	1.14
More than 10	6	0.10
Total	5766	100.00

  Source: Topographic Survey, 2010

The highest contour level is found in Ward no. 09 (10.24 mPWD) and the lowest height is also found in Ward no. 06 (3.61 mPWD).  On the other hand the highest average height found in Ward no. 03 (7.81 mPWD). The highest standard deviation of contour is in Ward no. 03 and 09 (1.05 and 0.90) and lowest in Ward no. 08 (0.53). Map 12.2 shows the topographic condition of Nabiganj Pourashava.

Proposal for Improvement of the Existing Drain Networks

Based on the results of drainage study it is recommended for the existing drain that:

·         Rehabilitate broken drains;

·         Cover the open drains based on budget allocation. 

·         Construction of new channels and rehabilitation of old ones with enough drainage head.

·         Remove all un-authorized structures, which developed on drainage structures.

·         Regular cleaning and maintenance by the concerned authorities.

·         Embarking on a sustained public enlightenment to discourage residents from dumping their refuse into drainage channels.

New Drains

Total 9.37 km secondary drain and 59.05 km tertiary drain proposed in drainage development plan. Table 3 shows the summary of proposed drainage facilities at Pourashava. In additional the Shakhaborak River will serve as the main out fall and main natural drainage network.

Table 3: Summary of proposed drain

Type of Drain	Length in M	Length in Km	%
Secondary Drain	9369.35	9.37	13.69
Tertiary Drain	59047.54	59.05	86.31
Total	68416.89	68.42	100.00