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APPLICATION OF THE FAST THEORY TO THE SEDIMENTOLOGY OF THE PAWMPAWM RIVER, GHANA

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

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APPLICATION OF THE FAST THEORY TO THE SEDIMENTOLOGY OF THE PAWMPAWM RIVER, GHANA

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  1. APPLICATION OF THE FAST THEORY TO THE SEDIMENTOLOGY OF THE PAWMPAWM RIVER, GHANA Divine OdameAppiah, Dept. of Geography and Rural Dev’t, KNUST, Kumasi GGA/GGTA ANNUAL CONFERENCE Held at KNUST, Kumasi From 1st to 4th 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

  8. RESULTS • Where, Qs = suspended sediment transport (tones/day); Qw = water discharge (m3/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 m3/s and 0.3555 m3/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 m3/s and 0.8366 m3/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 m3/s and 0.7130 m3/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!

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