Calculating the  sediment  budget  of  a  tropical  lake  in  the  Blue Nile basin: Lake Tana

Zimale, Fasikaw A.; Mogus, M. A.; Alemu, Muluken L.; Ayana, Essayas K.; Demissie, Solomon S.; Tilahun, Seifu A.; Steenhuis, Tammo S.

doi:10.5194/soil-2015-84

Cited by 19 publications

(24 citation statements)

References 28 publications

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“…Moreover, the mean sediment trapping efficiency ( T e ) of Lake Tana was also calculated from the measured sediment fluxes as 97%. This value is higher than the T e of 50% used in the Abay Basin Master Plan Study (BCEOM, ), but is consistent with the higher values documented by other authors (SMEC, ; Engida, ; Maes, ; Zimale et al, ).…”

Section: Resultssupporting

confidence: 91%

Revisiting lake sediment budgets: How the calculation of lake lifetime is strongly data and method dependent

Lemma

Admasu

Dessie

et al. 2017

Earth Surf Processes Landf

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Lake sedimentation has a fundamental impact on lake lifetime. In this paper, we show how sensitive calculation of the latter is to the quality of data available and assumptions made during analysis. Based on the collection of a large new dataset, we quantify the sediment masses (1) mobilized on the hillslopes draining towards Lake Tana (Ethiopia), (2) stored in the floodplains, (3) transported into the lake, (4) deposited in the lake and (5) delivered out from the lake so as to establish a sediment budget. In 2012–2013, suspended sediment concentration (SSC) and discharge measurements were made at 13 monitoring stations, including two lake outlets. Altogether, 4635 SSC samples were collected and sediment rating curves that account for land cover conditions and rainfall seasonality were established for the 11 river stations, and mean monthly SSC was calculated for the outlets. Effects of the floodplain on rivers' sediment yield (SY) were investigated using measurements at both sides of the floodplains. SY from ungauged rivers was assessed using a model that includes catchment area and rainfall, whereas bedload and direct sediment input from lake shores were estimated. As a result, the gross annual SY was c. 39.55 (± 0.15) Mt, dominantly from Gilgel Abay and Gumara Rivers. The 2.57 (± 0.17) Mt sediment deposited in floodplains indicate that the floodplains serve as an important sediment sink. Moreover, annually c. 1.09 Mt of sediment leaves the lake through the two outlets. Annual sediment deposition in the lake was c. 36.97 (± 0.22) Mt and organic matter accumulation was 2.15 Mt, with a mean sediment trapping efficiency of 97%. Furthermore, SSC and SY are generally higher at the beginning of the rainy season because soils in cultivated fields are bare and loose due to frequent ploughing and seedbed preparation. Later in the season, increased crop and vegetation cover lead to a decrease in sediment production. Based on the established sediment budget with average rainfall, the lifetime of Lake Tana was estimated as 764 to 1032 years, which is shorter than what was anticipated in earlier studies. The sedimentation rate of Lake Tana (11.7 ± 0.1 kg m−2 yr−1) is in line with the sedimentation rates of larger lakes in the world, like Lake Dongting and Lake Kivu. Copyright © 2017 John Wiley & Sons, Ltd.

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Section: Resultssupporting

confidence: 91%

Revisiting lake sediment budgets: How the calculation of lake lifetime is strongly data and method dependent

Lemma

Admasu

Dessie

et al. 2017

Earth Surf Processes Landf

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“…Khelifa et al (2016) reported daily runoff with NSE values of 0.64 for calibration and 0.68 for validation. Similar studies are in better agreement with these results (Addis et al 2016;Zimale et al 2016). For a study in the Gumara watershed by Zimale et al (2016), the NSE values for daily flows obtained were 0.70 for calibration and 0.77 for validation period.…”

Section: Runoff Calibration and Validationsupporting

confidence: 80%

“…These authors report NSE values for runoff simulations using SWAT of 0.64 and 0.68 for calibration and validation, respectively. In another study in the Gumara watershed by Zimale et al (2016), the NSE values for daily flows obtained were 0.70 for calibration and 0.77 for validation period, which is comparable with the UW and TW NSE values in the Gumara-Maksegnit watersheds. However, the model tends to underestimate sediment yield during calibration and validation periods for both watersheds.…”

Section: Discussionsupporting

confidence: 59%

“…Setegn et al (2010) reported that sediment loads of 30-60 t ha −1 year −1 were exported from the Lake Tana watersheds while Easton et al (2010) predicted a maximum soil loss of 84 t ha −1 year −1 in the Gumara watershed. Similarly, Zimale et al (2016) reported an average sediment yield of 49 t ha −1 y −1 from the Gumara watershed. There are also a number of simulation studies on sediment load prediction at the gauging stations near Lake Tana (Easton et al 2010;Setegn et al 2010;Kaba et al 2014;Zimale et al 2016) which confirmed the results of the current study conducted in the Gumara-Maksegnit watershed.…”

Section: Discussionmentioning

confidence: 99%

“…Similarly, Zimale et al (2016) reported an average sediment yield of 49 t ha −1 y −1 from the Gumara watershed. There are also a number of simulation studies on sediment load prediction at the gauging stations near Lake Tana (Easton et al 2010;Setegn et al 2010;Kaba et al 2014;Zimale et al 2016) which confirmed the results of the current study conducted in the Gumara-Maksegnit watershed.…”

Section: Discussionmentioning

confidence: 99%

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Prediction of soil and water conservation structure impacts on runoff and erosion processes using SWAT model in the northern Ethiopian highlands

et al. 2017

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Purpose Land degradation due to soil erosion is a serious threat to the highlands of Ethiopia. Various soil and water conservation (SWC) strategies have been in use to tackle soil erosion. However, the effectiveness of SWC measures on runoff dynamics and sediment load in terms of their medium-and short-term effects has not been sufficiently studied. Materials and methods A study was conducted in 2011 to 2015 in the Gumara-Maksegnit watershed to study the impacts of SWC structures on runoff and soil erosion processes using the soil and water analysis tool (SWAT) model. The study was conducted in two adjacent watersheds where in one of the watersheds, SWC structures were constructed (treated watershed (TW)) in 2011, while the other watershed was a reference watershed without SWC structures (untreated watershed (UW)). For both watersheds, separate SWAT and SWAT-CUP (SWAT calibration and uncertainty procedure) projects were set up for daily runoff and sediment yield. The SWAT-CUP program was applied to optimize the parameters of the SWAT using daily observed runoff and sediment yield data. Results and discussion The runoff simulations indicated that SWAT can reproduce the hydrological regime for both watersheds. The daily runoff calibration (2011)(2012)(2013) results for the TW and UW showed good correlation between the predicted and the observed data (R 2 = 0.78 for the TW and R 2 = 0.77 for the UW). The validation (2014)(2015) results also showed good correlation with R 2 values of 0.72 and 0.70 for the TW and UW, respectively. However, sediment yield calibration and validation results showed modest correlation between the predicted and observed sediment yields with R 2 values of 0.65 and 0.69 for the TW and UW for the calibration and R 2 values of 0.55 and 0.65 for the TW and UW for the validation, respectively. Conclusions The model results indicated that SWC structures considerably reduced soil loss by as much as 25-38% in the TW. The study demonstrated that SWAT performed well for both watersheds and can be a potential instrument for upscaling and assessing the impact of SWC structures on sediment loads in the highlands of Ethiopia.

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Retracted: Revisiting lake sediment budgets: how the calculation of lake lifetime is strongly data and method dependent

2017

Earth Surf Processes Landf

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The above article, first published online in Wiley Online Library (wileyonlinelibrary.com), and in Earth Surface Processes and Landforms on 19th February 2017 (10.1002/esp.4111), has been retracted by agreement between theauthors, the journal Editor‐in‐Chief, Stuart Lane, and John Wiley & Sons Ltd.The retraction has been agreed due to calculation errors which could constitute an environmental hazard if not corrected. Since publication of the above article, several colleagues have brought to the attention of the authors that the presented sediment budget is inconsistent with suspended sediment concentrations reported in the same manuscript. This was not picked up during the review or the editing process. The authors have revisited the huge measured dataset on which this paper is based and found indeed a systematic error in calculations of sediment fluxes, as they had been using a wrong constant in conversions from water pressure data recorded every ten minutes and suspended sediment concentration to annual sediment transport rates. This has resulted in an underestimation of sediment transport rates by all rivers by an order of magnitude.The authors apologise for these calculation errors, and, with agreement of all parties, it was decided that the appropriate corrective action is retraction of this paper. A new corrected version will be submitted to the journal. We apologise for any inconvenience the premature publication of this work may have caused our readers. Reference

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Calculating the sediment budget of a tropical lake in the Blue Nile basin: Lake Tana

Cited by 19 publications

References 28 publications

Revisiting lake sediment budgets: How the calculation of lake lifetime is strongly data and method dependent

Revisiting lake sediment budgets: How the calculation of lake lifetime is strongly data and method dependent

Prediction of soil and water conservation structure impacts on runoff and erosion processes using SWAT model in the northern Ethiopian highlands

Retracted: Revisiting lake sediment budgets: how the calculation of lake lifetime is strongly data and method dependent

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