Kimbiji Aquifer

Kimbiji aquifer comprises Kimbiji and Mpera wellfields, and is considered one of the main water sources in the Project Area. Data concerning the Kimbiji aquifer is presented herein after.

Hydrogeology

Hydrogeology of Kimbiji aquifer is presented below:
– Area 7,500 m2
– Aquifer thickness 900 km in the west and 1400 km in the east
– Porosity 30%
– Aquifer materials 70%
– Stored water 1,700 km3
– Conservative storage 1,000 km3
– Depth of saltwater 1,050 m (fresh water thickness)
– Static water depth Artesian flow for Kimbiji and 11 m for Mpera
– Salinity 1,100 mg/L
– Transmissivity 100 m2/d
– Discharge/drawdown 2.5L/s/m (10,800 m3/d at 50 m drawdown)
– Recommended well yield 13,000 m3/d

Well Characteristics

Characteristics of wells recommended for Kimbiji aquifer are presented below:
– Depth Up to 600 m
– Working time 16 hours
– Design yield 13,000 m3/d
– Ls 50% of the well depth
– Perforated area 10%
– Aperture 1 mm
– Gravel Well graded gravel pack
– Type Stainless screen “Johnson Type”
– Spacing 2,500 m

It should be noted that the production well can yield 15,000 to 20,000 m3/d in case of using Johnson Type screens for depth 800 m.

Low Kidunda Dam

According to the Water Source Option Review (WSOR) study, the present unregulated river does not provide a reliable source of surface water for a major city as DSM.
The maximum abstraction capacities of the Upper Ruvu and Lower Ruvu intake works are 210,000 and 386,000 m3/d respectively, so the absolute upper limit to the public water supply abstraction rate is 596,000 m3/d. According to the study, implementing the Kidunda Dam Project on Ruvu River shall guarantee a yield of 950,000 m3/d.

The proposed Kidunda Dam Key Data:
1. Located 168 km from the Indian Ocean
2. Coordinate: E: 413 545 m; N: 9 196 445 m
3. Dam embankment 87m from sea level
4. Embankment Height 21m,
5. Dam length 860m
6. Dam reservoir capacity 190mil m3.
7. Live storage 174 mil m3
8. Flow to Ruvu 24 m3/sec
9. Inundated area 55km2.
10. Power Generation 20MW

Mtoni Water Supply System

Water Treatment Plant (WTP)

The design capacity of the Mtoni WTP is estimated to be about 9,000 m3/d. Mtoni WTP which comprises the following:
– Intake on Kizinga River: Minimum flow recorded 0.036 m3/s in November 1971, maximum flow 2.9 m3/s in April 1968, design and operating capacity from 13,000 to 22,000 m3/d.
– Raw water pumping main: Cast iron DN 375 mm, 1 km long, capacity
0.12 – 0.16 m3/s.
– Grit removal: Sand trap not covered.
– Raw water pumping station: 4 compartment well sump, 4 x 4 x 5.4 m deep each, total volume 300 m3, inlet pipe DN 375 mm,
– Chemical Building: Chemicals dosed into flocculation chamber.
– Clarifiers: 6 units, vertical up-flow floc blanket type, dimensions 7.5 x 7.5 x 7.5 m depth each, total capacity 0.10 – 0.15 m3/s.
– Filters: 3 rapid gravity sand filters, each unit comprising 2 bays of dimensions
5.5 x 2.5 m.
– Disinfection: Post chlorination gas or hypochlorite injected via 35 – 50 mm diameter pipes.
– Clear water tanks: 2 compartment reinforced concrete rectangular tank, dimensions 54 x 38 x 4.5 m height, capacity 9,100 m3.
– Clear water pumping station: 2 single stage pumps of discharge 38 L/s each and head 35 m, 2 pumps of discharge 90 L/s and head 37 m and 2 multistage horizontal pumps of discharge 32 L/s and head 37 m.
Mtoni Transmission System
Mtoni transmission system is considered the oldest system commissioned in 1951 feeding southern and eastern part of Changombe, Kurasini, Mtoni, Tandika, Kigamboni and Mbagala. Mtoni transmission system comprises the following:
– A cast iron transmission main of length 1 km and DN 375 mm conveying raw water from the intake to the Mtoni plant, the main is in good condition. Hazen-Williams (H-W) friction coefficient (C-value) is assessed to be 100.
– Two transmission mains conveying treated water from the Mtoni plant directly to the distribution system, diameters varying from DN 150 – 375 mm. Pipe materials were CI, DI and PVC. The transmission mains have many off-takes along their route. C-value ranges from 90 to 100. The mains are in a satisfactory condition.
A tank of capacity 500 m3 at Mbagala, is connected to the treated water main in order to serve Mbagala area.