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Preliminary Investigation into the Hydropower Potential on Scottish Farms
J. agric. Engng Res. (1998) 70, 307—311 Articel Number: ag980288
RESEARCH NOTE
Preliminary Investigation into the Hydropower Potential on Scottish Farms R. Graham SAC, Resource Engineering Department, Bush Estate, Penicuik EH26 0PH, UK (Received 9 June 1997; accepted in revised form 4 February 1998)
The numbers of rivers and lochs which lay within the farm boundaries of a sample of 419 farms throughout Scotland were determined. This was done using GIS software with the Ordnance Survey digital data set ‘‘Strategi’’. The river length and head were also calculated for each farm. It was found that 82% of the farms had a river or loch within their boundaries, and 16% had a river with a high head difference of 50 m or greater, suggesting good potential for power generation. Existing water power features, shown as mill, weir or dam, were found on 5% of the farms. ( 1998 Silsoe Research Institute 1. Introduction Little is known about the distribution of hydroenergy resources on farms, particularly at sites where the power potential is relatively small. An earlier study of the smallscale hydroelectric generation potential in the UK, for installed capacities in the range 25 kW to 5 MW, concluded that a potential capacity of 322 MW could be developed economically, at an internal rate of return of 10%; of this, 286 MW or 89% was in Scotland.1 This preliminary study set out to provide more information on the potential of water power on Scottish farms. It examined how many, out of a sample of farms, had rivers within their boundaries, and certain features of these were assessed. The number of farms in the sample was some 3% of the total population of full time farmers, and the sample was stratified by farm type, size and location in order to provide proper representation of Scottish farming.2 The size of river was found from the attribute coding of Ordnance Survey features, and the river length and head were scaled. Existing water power features, shown as mill, weir or dam within a farm boundary were taken from hardcopy 1 : 25 000 or 1 : 50 000 OS maps. It was intended that this study would lead on to later specific analysis of the potential for hydropower generation on the farms. 0021-8634/98/070307#05 $30.00/0
2. Data sources and method ‘‘Strategi’’ is the digital representation of the Ordnance Survey’s Travelmaster map series, which is a geometrically structured, 1 : 25 000 scale, vector database that defines real-world geographic objects as point and line features. Each feature consists of geometric and attribute data. There are 121 different attribute codes covering communications, hydrology, settlements, administrative boundaries, land use and text. Water features in ‘‘Strategi’’ are split into seven different categories: there are six categories of river, based on river width, and one for lakes (Table 1). The data are split down into ‘‘squares’’ known as tiles with each tile covering an area 50 km]50 km; the whole of Scotland is covered by 78 tiles. The alternative of using the more detailed ‘‘Landline’’ data set, at a scale of 1 : 2500, with 40 000 tiles for the whole of Scotland, would have been unmanageable. The rivers and lochs from the 78 ‘‘Strategi’’ tiles covering the whole of Scotland were combined into one ARC/INFO GIS3 file. Maps with the farm boundaries were supplied by the 419 farmers in the sample. These were digitized and imported into ARC/INFO GIS software. The water features within the farm boundaries were then selected by overlaying one file with the other.
307
Table 1 OS feature code descriptions for water OS feature code 5211 5212 5213 5221 5222 5230 5250
Description Main river, source Main river, middle Main river, lower Secondary river, source Secondary river, lower Minor river Lake, margin
Width, m (4 4—8 '8 (4 4—8 (4 —
( 1998 Silsoe Research Institute
308
R . G RA H AM
Table 2 Number of farms with OS water features Main river
Secondary river
Source
Middle
Lower
Source
Lower
0 0
13 3
10 2
12 3
54 13
No. of farms %
Minor river
Loch
Any water feature
Any river
316 75
36 9
344 82
342 82
Total no. of farms: 419.
Existing mills, weirs and dams were found by visually examining the hardcopy 1 : 25 000 or 1 : 50 000 scale maps of the farm boundaries. The maximum possible river head on each farm was also calculated manually from these maps.
Table 3 Number of farms with mills, weirs and dams marked on OS 1 : 25 000 or 1 : 50 000 maps
No. of farms %
3. Results 3.1. ¼ater features The number of farms with OS water features, and the percentages from the total sample of 419 farms, are given in Table 2. This analysis shows that over 80% of the sample farms have at least one water feature, predominantly a minor river.
3.2. Existing water power features The number of mills, weirs and dams found on the 419 farms, are given in Table 3. This might indicate that water power was presently being used or that it was used in the past. In some cases the civil works would still be there and it may be possible to convert these for use with modern water turbines, thus saving on installation costs.
Mill
Weir
Dam
19 5
10 2
4 1
Total no. of farms: 419.
3.3. River length The length of river within each farm boundary was estimated as the straight line distance between the upper and lower points of the river, at or within the boundary, using Arcview.4 Water pipelines for hydropower are usually built in as straight a line as possible, as this is the lowest cost option.5 The lengths for all the farms are given as a histogram in Fig. 1. 3.4. River head The ‘‘Strategi’’ data set does not include height data and therefore the head or change in height of the river
Fig. 1. River length within farm boundary, for the 342 farms which have an OS river feature
HY D RO P O W ER PO TE NT I A L O N S CO T TI SH FAR M S
309
Fig. 2. River head within farm boundary for the 342 farms which have an OS river feature
within the farm boundary was estimated from 1 : 25 000 scale maps, where the contour interval is 5 m, or from 1 : 50 000 scale maps, where it is 10 m. Head differences less than the contour interval cannot be assessed accurately from these maps since they must be estimated from the distance to the nearest contour. Accuracy at low heads is important, because any head less than 2 m is considered inappropriate for hydropower generation using commercially available water turbines, and 2 to 3 m is considered uneconomic unless some of the civil
works are already in place, with the minimum of a weir.6 The histogram of estimated river heads is given in Fig. 2.
3.5. River gradient River gradient was calculated from head after dividing by length using the above values, and is shown as a histogram of inverse gradient for convenience in Fig. 3.
Fig. 3. Inverse river gradient within farm boundary for the 342 farms which have an OS river feature, e.g. 100 m/m is the inverse of 1 : 100 gradient
310
R . G RA H AM
Fig. 4. River head against length within farm boundary
Figure 4 shows a scatter plot of river head against length, to indicate whether or not farms with high head are associated with long rivers.
4. Discussion The majority of viable sites in the earlier study, 276 MW, were at locations with a head greater than 50 m. In the present study, there are 69 out of 342 farms with heads over 50 m (Table 4). Thus, 16% of the main sample of 419 farms have rivers with a possible head within the farm boundary that is greater than 50 m. These farms are most likely to have greatest potential for hydroelectric generation. However, as well as river head, river flow must be known in order to calculate the available power. River flows were beyond the scope of this study, but are now being investigated using computer software developed by the Institute of Hydrology.7 Also, some of the farms have a high head that occurs over
a considerable distance, which might make the scheme uneconomic due to high pipeline costs. As hydroelectric installations are very site-specific, the economics of sites must be examined individually. Assuming that the sample of 419 farms, is representative of the total 13 750 full-time farms in Scotland, then a high proportion, 41%, have rivers with medium to high head available. This would be equivalent to approximately 5600 farms. In practice, head is not the only criterion and some sites may prove impractical for reasons such as layout of the land, problems with connection to the electricity grid or being environmentally unsuitable.
6. Conclusions From a sample of 419 Scottish farms, 342 or 82%, had a river that was shown on the Ordnance Survey ‘‘Strategi’’ data set. There was a main river on 3% of farms,
Table 4 River head classification Site description Very low head Low head Medium head High head Total
River head (m) (3 3—10 10—50 '50
No. of farms
% of farms with rivers
% of all farms
88 79 106 69 342
26 23 31 20 100
21 19 25 16 81
HY D RO P O W ER PO TE NT I A L O N S CO T TI SH FAR M S
a secondary river on 13% of farms, and a minor river on 75% of farms, according to the OS classification. Sixty-nine farms or 16% had a river with a head difference within the farm boundary of 50 m or greater, suggesting good potential for power generation, and a further 25% had a head difference of 10—50 m. The river gradient, taken simply as the ratio of head to length, varied between farms from 1 : 20 to 1 : 600, while approximately three-quarters of the river lengths were less than 2 km. River flow and power estimates were outside the scope of this study but will be reported later. Up to 5% of the farms have a mill, weir or dam shown on the 1 : 25 000 or 1 : 50 000 OS map; some of these existing sites could be good candidates for viable development, depending on site conditions.
311
References 1
2
3
4
5
6
7
Small-scale hydroelectric generation potential in the UK Report No. ETSU-SSH 4063 P1-P3, ETSU, Harwell, UK, 1989. Profitability of farming in Scotland 1991/92 SAC Economic Report No. 42. SAC West Mains Road, Edinburgh, UK, 1993 Understanding GIS The ARC/INFO Method ESRI, 380 New York Street, Redlands, CA 92373, USA, 1990—1995 ArcView ESRI, 380 New York Street, Redlands, CA 92373, USA, 1994 Layman’s Guidebook How to develop a small hydro site. CEC (DGXVII, Directorate General for Energy), 1994 Small-scale hydro schemes Notes for developers (England & Wales). ETSU, Harwell, UK, 1996 HYDRA European Atlas of Small Scale Hydropower Resources. Institute of Hydrology, Wallingford, Oxon, UK, 1997
RESEARCH NOTE
Preliminary Investigation into the Hydropower Potential on Scottish Farms R. Graham SAC, Resource Engineering Department, Bush Estate, Penicuik EH26 0PH, UK (Received 9 June 1997; accepted in revised form 4 February 1998)
The numbers of rivers and lochs which lay within the farm boundaries of a sample of 419 farms throughout Scotland were determined. This was done using GIS software with the Ordnance Survey digital data set ‘‘Strategi’’. The river length and head were also calculated for each farm. It was found that 82% of the farms had a river or loch within their boundaries, and 16% had a river with a high head difference of 50 m or greater, suggesting good potential for power generation. Existing water power features, shown as mill, weir or dam, were found on 5% of the farms. ( 1998 Silsoe Research Institute 1. Introduction Little is known about the distribution of hydroenergy resources on farms, particularly at sites where the power potential is relatively small. An earlier study of the smallscale hydroelectric generation potential in the UK, for installed capacities in the range 25 kW to 5 MW, concluded that a potential capacity of 322 MW could be developed economically, at an internal rate of return of 10%; of this, 286 MW or 89% was in Scotland.1 This preliminary study set out to provide more information on the potential of water power on Scottish farms. It examined how many, out of a sample of farms, had rivers within their boundaries, and certain features of these were assessed. The number of farms in the sample was some 3% of the total population of full time farmers, and the sample was stratified by farm type, size and location in order to provide proper representation of Scottish farming.2 The size of river was found from the attribute coding of Ordnance Survey features, and the river length and head were scaled. Existing water power features, shown as mill, weir or dam within a farm boundary were taken from hardcopy 1 : 25 000 or 1 : 50 000 OS maps. It was intended that this study would lead on to later specific analysis of the potential for hydropower generation on the farms. 0021-8634/98/070307#05 $30.00/0
2. Data sources and method ‘‘Strategi’’ is the digital representation of the Ordnance Survey’s Travelmaster map series, which is a geometrically structured, 1 : 25 000 scale, vector database that defines real-world geographic objects as point and line features. Each feature consists of geometric and attribute data. There are 121 different attribute codes covering communications, hydrology, settlements, administrative boundaries, land use and text. Water features in ‘‘Strategi’’ are split into seven different categories: there are six categories of river, based on river width, and one for lakes (Table 1). The data are split down into ‘‘squares’’ known as tiles with each tile covering an area 50 km]50 km; the whole of Scotland is covered by 78 tiles. The alternative of using the more detailed ‘‘Landline’’ data set, at a scale of 1 : 2500, with 40 000 tiles for the whole of Scotland, would have been unmanageable. The rivers and lochs from the 78 ‘‘Strategi’’ tiles covering the whole of Scotland were combined into one ARC/INFO GIS3 file. Maps with the farm boundaries were supplied by the 419 farmers in the sample. These were digitized and imported into ARC/INFO GIS software. The water features within the farm boundaries were then selected by overlaying one file with the other.
307
Table 1 OS feature code descriptions for water OS feature code 5211 5212 5213 5221 5222 5230 5250
Description Main river, source Main river, middle Main river, lower Secondary river, source Secondary river, lower Minor river Lake, margin
Width, m (4 4—8 '8 (4 4—8 (4 —
( 1998 Silsoe Research Institute
308
R . G RA H AM
Table 2 Number of farms with OS water features Main river
Secondary river
Source
Middle
Lower
Source
Lower
0 0
13 3
10 2
12 3
54 13
No. of farms %
Minor river
Loch
Any water feature
Any river
316 75
36 9
344 82
342 82
Total no. of farms: 419.
Existing mills, weirs and dams were found by visually examining the hardcopy 1 : 25 000 or 1 : 50 000 scale maps of the farm boundaries. The maximum possible river head on each farm was also calculated manually from these maps.
Table 3 Number of farms with mills, weirs and dams marked on OS 1 : 25 000 or 1 : 50 000 maps
No. of farms %
3. Results 3.1. ¼ater features The number of farms with OS water features, and the percentages from the total sample of 419 farms, are given in Table 2. This analysis shows that over 80% of the sample farms have at least one water feature, predominantly a minor river.
3.2. Existing water power features The number of mills, weirs and dams found on the 419 farms, are given in Table 3. This might indicate that water power was presently being used or that it was used in the past. In some cases the civil works would still be there and it may be possible to convert these for use with modern water turbines, thus saving on installation costs.
Mill
Weir
Dam
19 5
10 2
4 1
Total no. of farms: 419.
3.3. River length The length of river within each farm boundary was estimated as the straight line distance between the upper and lower points of the river, at or within the boundary, using Arcview.4 Water pipelines for hydropower are usually built in as straight a line as possible, as this is the lowest cost option.5 The lengths for all the farms are given as a histogram in Fig. 1. 3.4. River head The ‘‘Strategi’’ data set does not include height data and therefore the head or change in height of the river
Fig. 1. River length within farm boundary, for the 342 farms which have an OS river feature
HY D RO P O W ER PO TE NT I A L O N S CO T TI SH FAR M S
309
Fig. 2. River head within farm boundary for the 342 farms which have an OS river feature
within the farm boundary was estimated from 1 : 25 000 scale maps, where the contour interval is 5 m, or from 1 : 50 000 scale maps, where it is 10 m. Head differences less than the contour interval cannot be assessed accurately from these maps since they must be estimated from the distance to the nearest contour. Accuracy at low heads is important, because any head less than 2 m is considered inappropriate for hydropower generation using commercially available water turbines, and 2 to 3 m is considered uneconomic unless some of the civil
works are already in place, with the minimum of a weir.6 The histogram of estimated river heads is given in Fig. 2.
3.5. River gradient River gradient was calculated from head after dividing by length using the above values, and is shown as a histogram of inverse gradient for convenience in Fig. 3.
Fig. 3. Inverse river gradient within farm boundary for the 342 farms which have an OS river feature, e.g. 100 m/m is the inverse of 1 : 100 gradient
310
R . G RA H AM
Fig. 4. River head against length within farm boundary
Figure 4 shows a scatter plot of river head against length, to indicate whether or not farms with high head are associated with long rivers.
4. Discussion The majority of viable sites in the earlier study, 276 MW, were at locations with a head greater than 50 m. In the present study, there are 69 out of 342 farms with heads over 50 m (Table 4). Thus, 16% of the main sample of 419 farms have rivers with a possible head within the farm boundary that is greater than 50 m. These farms are most likely to have greatest potential for hydroelectric generation. However, as well as river head, river flow must be known in order to calculate the available power. River flows were beyond the scope of this study, but are now being investigated using computer software developed by the Institute of Hydrology.7 Also, some of the farms have a high head that occurs over
a considerable distance, which might make the scheme uneconomic due to high pipeline costs. As hydroelectric installations are very site-specific, the economics of sites must be examined individually. Assuming that the sample of 419 farms, is representative of the total 13 750 full-time farms in Scotland, then a high proportion, 41%, have rivers with medium to high head available. This would be equivalent to approximately 5600 farms. In practice, head is not the only criterion and some sites may prove impractical for reasons such as layout of the land, problems with connection to the electricity grid or being environmentally unsuitable.
6. Conclusions From a sample of 419 Scottish farms, 342 or 82%, had a river that was shown on the Ordnance Survey ‘‘Strategi’’ data set. There was a main river on 3% of farms,
Table 4 River head classification Site description Very low head Low head Medium head High head Total
River head (m) (3 3—10 10—50 '50
No. of farms
% of farms with rivers
% of all farms
88 79 106 69 342
26 23 31 20 100
21 19 25 16 81
HY D RO P O W ER PO TE NT I A L O N S CO T TI SH FAR M S
a secondary river on 13% of farms, and a minor river on 75% of farms, according to the OS classification. Sixty-nine farms or 16% had a river with a head difference within the farm boundary of 50 m or greater, suggesting good potential for power generation, and a further 25% had a head difference of 10—50 m. The river gradient, taken simply as the ratio of head to length, varied between farms from 1 : 20 to 1 : 600, while approximately three-quarters of the river lengths were less than 2 km. River flow and power estimates were outside the scope of this study but will be reported later. Up to 5% of the farms have a mill, weir or dam shown on the 1 : 25 000 or 1 : 50 000 OS map; some of these existing sites could be good candidates for viable development, depending on site conditions.
311
References 1
2
3
4
5
6
7
Small-scale hydroelectric generation potential in the UK Report No. ETSU-SSH 4063 P1-P3, ETSU, Harwell, UK, 1989. Profitability of farming in Scotland 1991/92 SAC Economic Report No. 42. SAC West Mains Road, Edinburgh, UK, 1993 Understanding GIS The ARC/INFO Method ESRI, 380 New York Street, Redlands, CA 92373, USA, 1990—1995 ArcView ESRI, 380 New York Street, Redlands, CA 92373, USA, 1994 Layman’s Guidebook How to develop a small hydro site. CEC (DGXVII, Directorate General for Energy), 1994 Small-scale hydro schemes Notes for developers (England & Wales). ETSU, Harwell, UK, 1996 HYDRA European Atlas of Small Scale Hydropower Resources. Institute of Hydrology, Wallingford, Oxon, UK, 1997