2Department of Civil, Structural & Environmental Engineering, ... [3] Eco Fact Environmental Consultants, App 5D Bandon EIA - Fish Stock Assessment. 2011.
Sediment Surveying and Modelling on the River Bandon Gamble, J. 2, Harrington, J. 1, Barnett, D. 2, 1 School of Building & Civil Engineering, 2Department of Civil, Structural & Environmental Engineering, Cork Institute of Technology
Bandon Catchment
Flood Improvement Works
The River Bandon is located in the South Western River Basin District. The river rises in the Shehy mountain and flows east discharging to Kinsale Harbour. The Bandon River is 72km long with a catchment area of approximately 600km2 with an average gradient of 2.8m/km [1].
The River Bandon regularly floods with some of the largest floods occurring over the past decade. River improvement works are to be undertaken in the Summers of 2015 and 2016. These works include: 1. The dredging of the river for 3.6km from Bandon town. 2. Construction of a new two pier footbridge replacing the old seven pier bridge. 3. Flood walls and embankments to be constructed in the vicinity of Bandon town. 4. The drainage system of the town to be upgraded. 5. Construction of a new rock ramp fish pass at the Bandon weir.
Figure 1: The River Bandon Catchment [1]
The upstream reach of the River Bandon hosts the Freshwater Pearl Mussel (FWPM), which is an endangered species and is protected under the Habitats Directive. The FWPM Habitat has been selected as a special area of conservation (SAC). Downstream of Bandon town the river hosts Atlantic salmon and European eel, both are protected species under the red data list [3].
Ecology Upstream of Dunmanway consists of mountainous areas with poor soil while the lower reach of the river consist of low-lying agricultural land with good soil conditions. The largest town along the river is Bandon; the town is considered to be at a high risk of flooding [2].
Sediment Sampling
Suspended Sediment
Bed Load
Both suspended and bed load sediment samples have been taken from October 2013 to date. These samples have been taken at six locations along the river and its tributaries (Bridewell, Mill Stream and Brinny).
Suspended sediment samples were taken with both a depth integrating sampler and a grab sampler. The suspended sediment concentration (SSC) was determined by the filtration method [4]. CIT have operated and maintained a turbidity monitor on the River Bandon at Curranure since February 2010, with turbidity used as a surrogate for SSC. An automatic water sampler was installed at this location in August 2014 (see Figure 3).
Bed load samples were taken using a grab sampler and the samples were sieved to determine the particle size distribution [5]. D50 valued varied from 3.1 to 28.5mm. Three bed traps were placed in the river (two in the vicinity of Bandon town and one at O’Driscoll’s Bridge) in October 2014 (see Figure 4), the bed traps will aid the analysis of bed load transport.
Figure 2: Sediment Sampling Locations
Figure 3: Curranure Station Monitoring Equipment
Figure 4: Bed Trap
HEC-RAS sediment transport modelling requires the calibration of both water level and sediment characteristics where the predicted model water level is initially compared to observed water level data from the two hydrometric stations: Station 20001 at Bandon Bridge and Station 20002 at Curranure. The statistical parameters of Root Mean Squared Error (RMSE), Nash-Sutcliffe Coefficient of Efficiency (CoE) and Bias Error (BE) were applied to the calibration analysis as follows:
Initial model calibration results are presented in Table 1.
Numerical Modelling with HEC-RAS A HEC-RAS numerical model is being developed. The river reach modelled is from 1.3 miles upstream of Bandon town to downstream at Innishannon, with a total model length of 11km.
Table 1: Calibration analysis Station 20001 20002
Manning ‘n’ Coefficient 0.0332 0.0337
RMSE (m) 0.087 0.057
CoE
BE (m)
0.992 0.995
-0.021 -0.02
Validation of the predicted model water level was undertaken for a full year (01/10/09 to 30/09/10). The validation of the model provides satisfactory results (see Figure 6).
Figure 5: River Bandon Model Boundaries
The model also includes the River Bandon’s three main tributaries (Bridewell, Millstream and where: Brinny). Geometric data is based on river survey WSob= data from the OPW. A total of 239 river cross WSsim= sections are used in the model.
Water surface level observed at the hydrometric station Water surface level simulated by HEC-RAS Average water surface level observed at the WSobav= hydrometric station n= Number of reference measurements (data points)
References [1]
Harrington, J., Harrington, S., ‘Sediment & Nutrient Behaviour on the River Bandon, Ireland’, River Basin Management VII, pp. 215 – 226, New Forest, UK, May, 2013. [2] Heritage, G., Baseline Hydromorphological Assessment of the River Bandon through Bandon Town, County Cork, E. Russell & G. Heritage, Editor. 2011: JBA Consulting. [3] Eco Fact Environmental Consultants, App 5D Bandon EIA - Fish Stock Assessment. 2011. [4] American Public Health Association, American Water Works Association, and Water Pollution and Control Federation, 1995, Standard Methods for the Examination of Water and Wastewater, 1995, American Public Health Association, Method 2540D, pp. 256. [5] British Standard BS 1377-2: 1990 Soils for Civil Engineering- Part 2. 1990, British Standard.
Figure 6: Model Validation Analysis
Acknowledgements The authors wish to acknowledge the funding received from the OPW and Byrne Looby PHMcCarthy Consulting Engineers and from the OPW for providing water level data. The authors also would like to acknowledge the support of the UCD Centre for Water Resources Research in providing the automatic water sampler.
