1. APPLICATION OF THE FAST THEORY TO THE SEDIMENTOLOGY OF THE PAWMPAWM RIVER, GHANA Divine Odame Appiah, Dept. of Geography and Rural Dev’t, KNUST, Kumasi GGA/GGTA ANNUAL CONFERENCE Held at KNUST, Kumasi From 1 st to 4 th August, 2012 Theme: environmental sustainability and development; the Geographer’s Perspective

2. Introduction  Stream channel morphology is a function of sediment entrainment  Is it also a function of discharge and sediment yield. At different sub-links of the river (capacity, competence)  Interaction of precipitation, vegetation, runoff and erosion  Climate and geology are also essential controls on river channels  This was evident for the pawmpawm river system

3. Flow And Sediment Transport Theory (FAST) Approach  FAST: Flow And Sediment Transport  Intensive interrelationship between riverbed adjustment and bed load transfer (competence & capacity)  Both river bed geometry and bed load transfer are controlled by the development of flow cells  The FAST theory considers links in continuum as the operative criteria of sediment generation and discharge

4. Problem justification  Small rivers have been glossed over in many fluvial geomorphologic studies  Pawmpawm river demonstrates peculiar hydrologic characteristics that makes it amenable for studies  Coupled with the increasing changing human landuses in the basin.  Have tendencies to affect the sediment and water inputs (Kirkby and Rice, 1994)

5. Materials and methods  Current meter and wadding rods used for V, A, s =Q data, relevant for the estimation of the sediment concentration  Two gauges were installed at Huhunhya and Oterkpolu and daily-monitored.  In all, five flow measurements were taken at each station  Sediments in Petri dishes in ovens at 70C. To determine gross and net weights in mg/l WRI Laboratory. Decantation and heating of samples for the suspended  Generation of discharge and sediment rating curves (EXCEL)

6. Study area

7. Morphometry of the Pawmpawm river ParametersMeasurements Total Length452.69 km Area of the21 km 2 Length of Channel40.60 km Slope of Channel4. 87 m/km Maximum Length of Basin8.20 km Areas of Circle with Same Perimeter22.79 km 2 Total No. of Streams (Ordered)217 Amplitude (456-91) m365m/ 0.365 km

8. RESULTS Where, Q s = suspended sediment transport (tones/day); Q w = water discharge (m 3 /s); Cs = suspended sediment concentration (mg/l) and 0.0864 = conventional constant (Ǿrstein, 1979)

9. Results cont... The sediment rating curves with water discharge for days only water levels were measured. Generally, the power function derived from the log–log slopes is commonly used to provide a fit between measured water and sediment discharges in the following relationship: (Gosseline and Craig, 2002)

10. A Rating Curve for Osubo

11. Results cont… The lowest and highest discharge values recorded for the Osubo were 0.1953 m 3 /s and 0.3555 m 3 /s, Corresponding to gauge heights of 0.30 m and 0.38 m respectively.

12. Rating Curve for Huhunya

13. Discharges measured from Huhunya were 0.44 m 3 /s and 0.8366 m 3 /s, with gauge heights of 0.20 and 0.40 m respectively The highest and lowest recorded water levels were 0.84 m and 0.40 m respectively. These values yielded discharge values of 1.5841 m 3 /s and 0.7130 m 3 /s respectively.

14. Rating curve for Oterpkolu

15. SST for Huhunya

16. SST for Oterkpolu

17. Results cont… The minimum and maximum sediment discharges at the Oterkpolu gage station were 1.4066 and 8.0248 tonnes/day respectively Typically, sediment-rating curves plotted on logarithmic scales have large slopes at low discharges and smaller slopes at high discharges.

18. Conclusions/implications  The likelihood for the sediment load of the river to increase if... basin degradation  The implication on the Volta lake sedimentation at the confluence…  ‘Suspended load of the river does not necessarily change with discharge downstream’ rejected by the t-test analysis.

19. Vegetable farm in close proximity to the river

20. Implications Anthropogenic influences on the river basin were considerably high e.g. Farming Some farms were seen located closer than the buffer zone of usually 30-40 metres from the river banks. De-vegetation activities for fuelwood were identified. Coupled with other land use activities within the basin, the River basin considerably impacted.

21. Heavily silted bridge

22. Abandoned Bridge Tack so mycket!