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HomeMy WebLinkAbout06_CFNM_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 combined Cape Fear / Neuse 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, broken out by basin and progressing downstream in each basin. The Neuse Basin model weighting is described in detail first. The rationale for the Cape Fear Basin model weighting is similar. 3 Section 2. Eno River Area – Neuse River Basin The reservoirs on the Upper Eno are in the 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 Orange Upstream Pond 1010 1050 WFER (West Fork Eno River) 1050 1000 375 275 -60 Lake Orange 1060 1000 375 275 -60 Corp. Lake 1080 500 Lake B. Johnston 1100 500 Other weights in the area include: Description Node/arc Number Weight WFER Min. Release 1050.1080 400 Orange Min. Release 1060.1080 400 Or-Alamance Demand 1046 250 WFER_Ag Demand 1052 1050 Or_Pond_Ag Demand 1062 1100 Piedmont Minerals Dem 1080 250 Hillsborough Demand 1106 250 EnoDurha_Ag Demand 1112 240 Hills. Channel Loss (Target) 1110.1107 +1000 -1000 The Orange (Upstream) Pond agricultural demand has the highest weight of 1100. This is higher than the Orange Pond weight to ensure that demand is met first before letting water flow downstream to Orange Pond. Orange Pond only has one zone (which is always assigned to the A-zone), and this weight is set higher than that of Lake Orange to prevent releases to Lake Orange when the pond is below full. The only reason the pond will draw down is net evaporation on the lake surface, which is modeled as a constraint and therefore does not use weights. The B- and C- Zone storage weights on WFER and Lake Orange are lower than the weights for their respective minimum flows, but higher than the downstream demands, since the minimum release is dictated by the amount that can be withdrawn from the lakes to meet demands. Note that the weights for the zones for both reservoirs are the same because their usable storage includes everything from the top of dead storage to the top of the normal pool. For the D zone, weighting is usually negative in order to discourage storing water in this zone, 4 which is commonly used for flood storage. Water will only be stored if there is a limit on downstream releases during a high inflow event. Corporation Lake and Lake Ben Johnston only have one storage zone. The weights are higher than weights on uses immediately downstream because they are run of river reservoirs and should remain full. The weighting on the C-zones on the upstream WFER and Lake Orange facilities is lower to ensure that water is withdrawn from this usable storage zone (excluding the A-zone for these reservoirs, which in this case represents dead storage) to keep Corporation Lake and Lake Ben Johnston full. Weighting in OASIS can also be done with target commands, in which case a penalty is assigned for being above or below the target. A target is applied to the Eno River channel loss. Every unit of water in excess (+) of the computed target for channel loss is penalized a 1000 points and every unit of water below (-) the target is penalized a 1000 points. Since the penalty for going above or below is the same, the model will meet the computed channel loss exactly. Furthermore, because the overall value is higher than any other in the system, the computed channel loss will always be met before other “goals”. All of the storage weights for this reach are higher than downstream weights (see following sections) to ensure that releases are not made to meet downstream needs (e.g., Falls Lake). 5 Section 3. Upstream of Falls Lake – Neuse River Basin As with the Eno, these reservoirs are in the 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 Lake Michie 1140 1000 350 250 -60 Little River Res. 1200 1000 350 250 -60 Lake Holt 1250 1000 350 250 -60 Lake Rogers 1270 5000 350 250 -60 Other weights in the area include: Description Node/arc Number Weight Durham Demand 1162 300 SGWASA Demand 1256 300 Creedmor Demand 1060 300 Michie_Ag Demand 1142 550 LitRes_Ag Demand 1202 550 Little River min. release 1200.1205 450 Durham Res. Balance (Target) 1140, 1200 2 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. It is assumed that the minimum release from the Little River Reservoir has priority over water supply withdrawals from the reservoir. Agricultural demands are weighted higher than lake withdrawals and B- and C- zone storage since they represent upstream irrigation withdrawals. For Durham’s two reservoirs, a balancing target with a low weight attempts to bring down the reservoirs proportionally, after other higher weight requirements have been met. All of the storage weights for this reach are higher than downstream weights (see following sections) to ensure that releases are not made to meet downstream needs (e.g., Falls Lake). 6 Section 4. Falls and Beaverdam Lakes – Neuse River Basin The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D Falls, Beaverdam 1300, 1230 200 200 50 -5 Other weights in the area include: Description Node/arc Number Weight Raleigh Demand 1306 100 Falls_Ag Demand 1302 230 Falls min. release 1300.1310 100 Clayton min. flow 1630.1640 125 Falls flood operation rules (target) 1300 +50 -50 Downstream flood control (targets) 1630.1640, 1780.1790, 1800.1850 +10 -0 Beaverdam elevation (target) 1230 +10000 -10000 Beaverdam release (targets) 1230 +1000 -1000 The weights for Raleigh demand and demands between Falls and Clayton (see tables below) are higher than the C zone weight for Falls to ensure these demands are met. The Corps implicitly accounts for withdrawals between Falls and Clayton when determining what releases need to be made from Falls to meet the Clayton minimum flow. Since the water quality storage is used for making minimum releases, and this storage is represented by zone C, the minimum release weight is higher than the C-zone weight. Zone B in Falls Lake is not used for meeting minimum release, hence its higher storage weight relative to the minimum release weight. Raleigh’s demand can also be met from Lake Benson, which is dictated by OCL as shown in Appendix A. Note that there is also a constraint on Raleigh’s demand, where the delivery will be zero from Falls Lake if the Falls water supply account is empty. A similar constraint is imposed on the minimum release if the Falls water quality account is empty. All of the storage weights are higher than weights for demands downstream of Clayton (see following sections) to ensure that releases are not made for these demands. The flood control targets are weighted such that the Corps’ recommended flood control operations are followed. The goal is to store water in the lake to avoid causing flooding downstream. The downstream flood control targets are weighted lower, which means they have less priority than the elevation-based flood operating rules. However, the combined minimum 7 release and Clayton minimum flow target weight is set high enough to ensure that those flows are always met. The target for Beaverdam elevation applies when Falls Lake is at or above 249 feet. At this elevation, Beaverdam and Falls become one pool, and the weight ensures that that the elevations for both track the same at or above 249. The Beaverdam target for releases relate to the drought release protocol for transfers of water from Beaverdam into Falls. 8 Section 5. Middle Basin – Neuse River Basin The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D Wake Forest Lake 1290 500 250 250 -10 Crabtree impoundments 1400 – 1418, 1422 250 Lake Wheeler 1420 500 50 50 -10 Lake Benson 1440 500 60 40 -10 Lake Johnson 1445 250 Lake Raleigh 1450 200 Johnston Co. Active Quarry 1647 20 Johnston Co. Aband Quarry 1648 20 Other weights in the area include: Description Node/arc Number Weight Swift Min. release 1440.1700 100 Burlington Ind. Demand 1318 75 Clayton_Ag Demand 1632 75 Middl_Ag Demand 1480 30 Johnston Co. Demand 1646 25 Johnston Co. Intake 1 1650.1654 50 Smithfield Demand 1666 25 The reservoirs all have weights higher than downstream demands. B- and C- zone Wheeler/Benson storage is weighted lower than the required minimum release. The storage weights in Benson and Wheeler are set up to allow, if the Raleigh withdrawal from this system is activated, drawdown of 2 feet from Benson first, subsequent release from Wheeler, and then draw down the rest of Benson. This is done to minimize spill and maximize yield. Lakes Raleigh and Johnson are not being used for water supply in the basecase (year 2010 demand) scenario and therefore only have one storage zone. Johnston County has two quarries available for offline storage. The operations for filling the quarries are controlled by OCL. The storage weights for the quarries allow withdrawals to be made when needed. The weight on Johnston County’s Intake 1 arc is used to set a target withdrawal from that intake. 9 Section 6. Lower Basin – Neuse River Basin The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D Buckhorn Reservoir 1500 1000 350 250 -10 Little River Reservoir (Raleigh Proposed) 1740 250 Other weights in the area include: Description Node/arc Number Weight Buckhorn Min. release 1500.1520 400 Buckhorn_Ag Demand 1502 550 Wilson Demand 1506 275 Litpr_Ag Demand 1752 30 Progress E. Demand 1766 25 Golds_Ag Demand 1782 30 Goldsboro Demand 1786 25 Kinst_Ag demand 1802 30 NRWASA Demand 1806 25 Weyer_Ag Demand 1802 30 Weyer. Demand 906 25 On Contentnea Creek, Buckhorn’s B- and C- Zone storage weights are lower than the minimum release requirement, and the C- zone weight is lower than the downstream Wilson demand weight, which allows the reservoir to be used for those purposes. The Buckhorn agricultural demand is weighted higher since it represents upstream irrigation withdrawals. Raleigh’s proposed Little River Reservoir, which is included in the model for planning purposes, only has one storage zone because it is not active in the basecase scenario. The other demands in this area are set lower to prevent any releases from upstream storage to meet demand. 10 Section 7. Upstream of Jordan Lake – Cape Fear River Basin The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D Reidsville Dam 0030 1000 350 250 -20 Old Stony Creek Res. 0070 1000 350 250 -20 Lake Higgins 0112 2000 400 300 -20 Brandt Res. 0120 1500 350 250 -20 Greensboro/Townsend Res. 0140 1000 325 200 -20 Graham Mebane Res. 0320 1000 350 250 -20 Mackintosh Res. 0340 1000 350 250 -20 Cane Creek Res. 0390 1000 350 250 -20 Stone Quarry 0395 1000 375 275 -20 University Lake 0430 1000 350 250 -20 Other weights in the area include: Description Node/arc Number Weight Reidsville min release 0030.0040 400 Brandt min release 0120.0140 400 Greensboro/Townsend min release 0140.0145 375 Graham Mebane min release 0320.0100 400 Cane Creek min release 0390.0370 400 Rockingham_40% 0021 550 Reidsville Demand 0031 300 Rockingham_60% 0041 100 Guilford_13% 0043 100 Guilford_20% 0051 100 Alamance_35% 0081 100 Caswell_100% 0083 100 Forsyth_50% 0111 550 Greensboro Total Demand 0123 350 Burlington to Greensboro Transfer 0071.0121 100 Greensboro Townsend withdrawal 0140.0121 100 Guilford_40% 0161 100 Orange_40% 0311 300 Graham Mebane Demand 0321 300 Guildford_15% 0331 300 Burlington Demand 0341 300 Alamance_Other_35% 0361 100 Alamance_30% 0371 100 Orange_24% 0381 550 Pittsboro water supply 0401 100 Chatham_50% 0403 100 Wake_75% 0411 100 11 Description Node/arc Number Weight OWASA Demand 0431 300 Orange_36% 0441 100 Durham_100% 0461 100 The reservoirs all have weights higher than downstream demands. B- and C- zone storage for reservoirs with minimum release requirements are weighted lower than the associated minimum release arcs. Reservoir demands are set higher than C- zone weights, but lower than B- zone weights. Agricultural demand weights are set higher than B- and C- zone storage. To simplify the handling of agricultural withdrawals, agricultural demand is often modeled as a withdrawal from a reservoir even though it would actually occur upstream. It is assumed these withdrawals would occur except under very dry conditions, thus effectively lowering inflow to the reservoir, so we allow the model to provide for these withdrawals from the reservoir except in extreme conditions when the reservoir has reached dead storage. All weights in the upper portion of the basin are set high enough to prevent operations downstream (at Jordan Lake, etc.) from impacting upstream operations. Weighting for OWASA’s system is set up to mimic their standard operating policy. The specific operating rules are set in OCL, but the weighting dictates that Stone Quarry will be used after the primary sources, Cane Creek Reservoir and University Lake. Greensboro has additional weights on certain arcs to control the flow of water from their reservoirs and from outside sources. The operations are set in OCL. 12 Section 8. Jordan Lake – Cape Fear River Basin The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D Jordan Lake 0470 200 200 5 -5 Other weights in the area include: Description Node/arc Number Weight Jordan Release 0470.0480 25 Jordan Flood Targets 0470.0480 10 Downstream Flood Targets (Lillington, Fayetteville) 0550.0555, 0740.0770 7, 7 Cary Apex water supply 0471 100 Chatham water supply 0473 100 RTP Demand 0474 100 Jordan Make Up Demand 0475 100 Morrisville demand 0477 100 Orange Co Demand Jordan 0921 100 Demand and minimum release weights on Jordan Lake are higher than the C- Zone storage weights. The weighting rationale is similar to Falls Lake, which also has water supply and water quality storage zones and associated minimum releases downstream. The complex operations for Jordan water supply and water quality accounting, downstream releases (including setting the Lillington target), and flood operations are modeled using OCL (see Appendix A). The flood control targets are weighted such that the Corps’ recommended flood control operations are followed. The goal is to store water in the lake to avoid causing flooding downstream; in Jordan Lake this is accomplished by increasing the release compared to the previous day by a maximum amount during a flood event. The downstream flood control targets are weighted lower, which means they have less priority than the elevation-based flood operating rules. However, the combined minimum release and Lillington minimum flow target weight is set high enough to ensure that those flows are always met. All of the storage weights are set to allow for releases to meet the demands and minimum flow targets downstream to Lillington, but not for releases for needs further downstream, reflecting how the Corps of Engineers operates Jordan Lake . 13 Section 9. Cape Fear River downstream of Jordan – Cape Fear River Basin The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D Harris Lake 0520 500 3 3 -5 Harris Aux. Res. 0528 275 0 0 0 Glenville Res 0760 500 5 2 -5 Other weights in the area include: Description Node/arc Number Weight CF Lillington target 0550.0650 25 Chatham_5% 0481 100 Allied Signal water Demand 0483 100 Progress Cape Fear water supply 0487 100 Sanford Water Supply 0491 100 Lee_38% 0511 100 Progress Harris Demand 0521 300 Wake_20% 0531 300 Wake_5% 0541 100 Harnett County water supply 0551 100 Holly Springs Demand 0923 100 Harnett_35% 0553 100 Dunn Demand 0663 2 Lee_55% 0671 2 Harnett_Other_50% 0681 2 Harnett_15% 0691 2 Carthage Demand 0701 2 Moore_35% 0713 2 Ft. Bragg Demand 0721 2 Fayetteville Demand 0733 4 Cumberland_45% 0741 2 Monsanto water supply 0771 2 Hoke_100% 0773 2 Cumberland_40% 0775 2 Dupont WS 0781 2 Cumberland_15% 0783 2 LCFWSA Bladen Bluff Demand 0785 2 Bladen_20% 0801 2 Bladen_60% 0811 2 Bladen_Other_20% 0821 2 Wilmington Demand 0823 2 Lower Cape Fear WSA Demand 0825 2 14 Note weighting on demands downstream of Lillington is less than weighting on reservoir storage upstream, namely Jordan Lake, meaning reservoir releases will not be made to meet these demands. Weighting of Harris Lake is set up to allow for a power plant withdrawal, but not to release water downstream for Lillington 15 Section 10. Deep River – Cape Fear River Basin The reservoir storage weights in this area are: Storage Zone Weights Reservoir Node Number A B C D High Pt 0220 1500 400 250 -20 Randleman 0270 1000 350 250 -20 Ramseur 0300 1000 350 250 -20 Siler City Upper Res. 0324 1000 240 240 -20 Siler City Lower Res. 0325 900 250 230 -20 Other weights in the area include: Description Node/arc Number Weight High Pt min release 0220.0230 425 Randleman min release 0270.0280 375 Siler City Release 0325.0328 325 Forsyth_Other_50% 0211 550 High Point Service Area Demand 0223 300 Guildford_12% 0231 100 City of Randleman Demand 0261 100 Randolph_Other_36% 0263 100 Randolph_28% 0281 100 Ramseur Demand 0301 300 Siler City demand 0327 300 Randolph_36% 0581 100 Robbins Demand 0591 100 Montgomery_100% 0593 100 Moore_25% 0595 100 Pilgrims Pride WTP 0601 100 Moore_40% 0603 100 Goldston Gulf water supply 0605 100 Chatham_45% 0621 100 Lee_7% 0623 100 Jamestown Demand 0903 300 Archdale Demand 0904 300 Randolph Co Demand 0906 300 Weighting of Siler City’s reservoirs is set up to simulate their operating policy of using the upper reservoir to keep the lower reservoir one foot below full until the upper reservoir is empty, and to allow for a minimum release from the lower reservoir. See Appendix A for the detailed OCL that dictates operations.