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Home My WebLink About04_RRHM_Appendix_D_-_Model_Weighting_Description 1 APPENDIX D – Model Weighting Description 2 Section 1. Introduction This report provides a detailed account of the weighting of nodes and arcs in the Roanoke River Basin model. OASIS uses a linear program solver, which means that it tries to maximize the overall value of allocating water subject to the goals (which have associated weights) and constraints (which must be met). The general strategy with goal-setting is to assign weights to mimic the real-world operating goals. For example, setting a reservoir’s storage weight higher than that of an unassociated demand downstream will prevent water from being released from that reservoir to meet the demand. Weighting is also used to properly dictate minimum releases and other flow targets. In general, positive weights encourage action and negative weights discourage action. Storing water, meeting demand, and meeting flow targets all have positive weights. If pumping can be avoided in favor of gravity flow, the pumping arc will have a negative weight, the gravity flow arc a positive weight. The model solver will gain more points by allocating each increment of flow to the positive-weight arc. Weighting is mostly relative. If the weight in storage (say 2) is higher than a weight for demand (say 1), the demand will not be met. Minimum flow weights are handled differently at times since they can be additive. If there are multiple minimum flow locations downstream of a reservoir, OASIS will assign value to the minimum releases based on the sum of those weights. So if there are three locations, each having a weight of 1, the model will get 3 points releasing water from an upstream reservoir to meet the minimum flows. If the storage weight is 2, then the reservoir will draw down to meet the minimum flows. Flow exceeding the minimum flow does not get any additional value. The user manual for OASIS provides more description on how model weighting works. Reservoirs can have up to four zones to which weights can be assigned. The A zone is below dead storage (which is generally non-usable storage). Often this represents the sediment pool, which could be tapped in an emergency situation. The B zone is between dead storage and the lower rule curve. This zone may be usable depending on the purpose. It might be used to maintain minimum releases from the lake, but not used or avoided for water supply because the intake does not extend down to that zone or because the water quality is poor. The C zone is the zone between the lower and upper rules, in which the lakes normally operate. The D zone is above the upper rule curve and below the maximum storage and is usually reserved for flood storage. Note that some reservoirs, including those being modeled as run-of-river, may only need one storage zone. This can simplify the number of weights in larger systems, but is generally not recommended because the model may draw into dead storage, down to the minimum storage in the elevation-storage-area table (even though physically it would not be possible to do), if the storage weight is less than weights for other uses. Each section of this document describes a portion of the model, progressing downstream in the basin. 3 Section 2. Upper Roanoke River Smith Mountain and Leesville reservoirs are in the headwaters of the Roanoke, and therefore proper weighting must be set up to prevent water being released to meet unrelated needs further downstream. The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D SmithMtn 100 10000 100 50 -2000 Leesville 200 10000 100 50 -2000 Other weights in the area include: Description Node/arc Number Weight Leesville Release 200.215 5000 Leesville Leakage 200.206 1000 WVWA 015 110 Salem 025 110 Rocky Mount 055 110 SM_Lee Ag 101 120 Bedford 214 90 Altavista (Town) 217 90 Dominion Altavista 218 90 Burlington Ind. 219 90 Altavista Ag 221 90 Brookneal Ag 241 90 Brookneal Dem 242 90 Dominion Pittsylvania 243 90 Boxley 244 90 Campbell Co 245 90 Keysville 246 90 Old Dominion Clover 248 90 The C- zone storage weights on reservoirs are all set lower than their associated withdrawals, which allow withdrawals to be made. For reservoirs with a minimum release, the B- zone weight is lower than the weight on the release arc. Agricultural demands are weighted higher than lake withdrawals and B- and C- zone storage since they represent upstream irrigation withdrawals. Note that operations of the Smith Mountain system are complex, and much of the operations are defined using OCL commands in addition to weighting (See Appendix A). 4 Section 3. Dan and Smith Rivers As with the Smith Mtn / Leesville, Philpott is in headwaters of the basin, and therefore proper weighting must be set up to prevent water being released to meet unrelated needs further downstream. The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D Philpott 300 10000 100 50 -2000 Other weights in the area include: Description Node/arc Number Weight Philpott Bypass 300.301 1000 Philpott Release 300.302 1000 Hanes 305 110 Francisco Ag 312 110 Belews Ck Steam Station 313 110 Madison Demand 315 110 Philpott Ag 316 120 Stuart 319 110 Mayo Ag 321 110 Mayodan 325 110 Wentworth Ag 331 110 Dan River Steam Station 332 90 Eden 335 110 Eden Ag 341 90 Paces Ag 347 90 Clarksville 364 50 Yanceyville 365 90 Dan R. Inc. 851 110 Martinsville 856 90 CP Films 857 90 Henry Co. 858 90 Danville 861 90 The C- zone storage weights on reservoirs are all set lower than their associated withdrawals, which allow withdrawals to be made. For reservoirs with a minimum release, the B- zone weight is lower than the weight on the release arc. Agricultural demands are weighted higher than lake withdrawals and B- and C- zone storage since they represent upstream irrigation withdrawals. Note that operations of Philpott are complex, and much of the operations are defined using OCL commands in addition to weighting (See Appendix A). 5 Section 4. Kerr, Gaston and Roanoke Rapids The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D Hyco 370 10000 500 500 -1000 Mayo 380 10000 500 500 -1000 Kerr 400 9900 40 0.9 -500 Gaston 600 10000 100 50 -900 Rapids 700 10000 95 45 -2500 Other weights in the area include: Description Node/arc Number Weight Hyco Release 370.390 2000 Mayo Release 380.390 2000 Kerr Bypass 400.401 1100 Kerr Release 400.600 1000 Rapids Bypass 700.701 1000 Rapids Release 700.720 1000 Hyco Ag 373 750 Roxboro Steam Electric 374 600 Roxboro 375 700 Mayo Steam Electric 377 600 Kerr Ag 403 60 KLRWS 405 50 Va_Corrections 406 50 MeckCogen 407 110 Unallocated VA Supply 408 50 Unallocated NC Supply 409 50 Gaston Ag 603 120 RRSA 605 110 VaBeach 695 110 Rapids Ag 703 105 RRapids 705 100 Rapids Mill 706 10 Weldon Demand 715 10 Hamilton Ag 803 20 Hamilton 805 10 Enterprise Farms 806 10 Gretna 868 90 Chatham 869 90 Halifax 870 90 The C- zone storage weights on reservoirs are all set lower than their associated withdrawals, which allow withdrawals to be made. For reservoirs with a minimum release, the B- zone weight 6 is lower than the weight on the release arc. Agricultural demands are weighted higher than lake withdrawals and B- and C- zone storage since they represent upstream irrigation withdrawals. Note that operations of Kerr/Gaston/Rapids are complex, and much of the operations are defined using OCL commands in addition to weighting (See Appendix A).