HomeMy WebLinkAbout6 - Boulder Creek Water Rights Computer Model
Understanding Boulder's Raw
Water Model
Capabilities and uses for water
planning and policy
Water Resources Advisory Board
May 17, 2009
Goals of this effort
• Provide WRAB with a better understanding of
what the Raw Water Planning Model does and
how it works.
• Establish a set of summary outputs from the
model for use as evaluation tools
• Explore the information provided by the model
over the longest period of time available
• Show some results in a way that provides
WRAB with a better understanding of the City's
Raw Water System
Central Resource Allocation Model
(CRAM)
• Network model originally developed for transportation
systems
• Consists of a series of links, each of which has a
capacity and a cost.
• Uses an algorithm to solve highly complex systems in a
way that minimizes the cost (or in our case maximizes
the water flowing through the most senior rights).
• It will always seek to satisfy demands, no matter what
the cost, as long as there is capacity to do so.
• Or, if there is a shortage is is because there is a physical
inability to satisfy the demand (primarily due to a lack of
capacity).
The model we were provided
• At request of WRAB, city water resources
consultant ran the raw water model under the
following conditions:
- Annual raw water demand set to 28599 of/year
- Expanded historical hydrology from tree ring studies
covering 285 years (1703-1987) NOTE: THIS RUN
DOES NOT INCLUDE 2002
- Uses current inventory of Boulder's water rights.
- Tracks deliveries and shortages on a 48 time step per
year interval.
What we asked to see...
• Use of the 450 year record to do the analysis.
• Verification of how water losses are account for in the demands.
• Capability to allow demands to vary with weather.
• Max and min yearly storage contents in each major reservoir group
(Barker, Silver Lake, Boulder Reservoir)
• Annual yields of direct flow rights by group (Barker, Silver Lake, CBT
Exchange, CBT Direct, Farmers)
• Water supplied from storage group (Barker, Silver Lake, Boulder
Reservoir)
• Annual deliveries, shortages, storage index (calculated from SWMP)
• Disaggregated data on Windy Gap use
• Operations at 3 demand levels (low, current build out, high enough
to get maximum yields of all rights.)
• Analysis of frequency of droughts at each level.
Requested output
Drought Stage Low Raw Water Current best estimate High Raw Water
(and target probability) Demand of buildout raw Demand
(-20 kaf at buildout) Water demand (-50 kaf)
(-30 kaf = 26 kaf +
loss allowance)
1 yr 2 yr 5 yr 1 yr 2 yr 5 yr 1 yr 2 yr 5 yr
1(1-20)
II (1:50
111 (1-100)
IV (1:1000)
O rvdel I Flows
14.0% 120%
12.0%
100%
10.0%
~n4ra
Estimated Probabilities;
8.0/4 1:1000 = < 15,000 of
4) 1:100 = 23,000 of T
U- 1:50 = - 26,000 of0°ta E
ac 6.0% 1:20 = 31,000 of
1:2 = 55,000 of
40°/a
4.0%
0%
2.0% -
Q,0% 0%
0 a 0 0 0 0 0 a a 0 a 0 0 0 0 0 a a 0 a 0 0 0 0 0 a a 0 0 0
_ _ = o = 0 = = o = a = = 0 = = o c (M = o = = c = a o = o =
0 0 0 o v 0 a 0 o v 0 R v o v o a v o o o R o 0 0 0 o a v
u i 4ri 4 W) 0 6n Ca Sa i 0 4n io u i c un 0 %0 0 0 Q ari U Idn k n
O £7
r r C4 C4 4e7 M Ln 47 W M r~ Iti CO CO 65 M = O T T iV MI h? M u7
T T T T T T T T T T T
Annual Flow (AF)
I•Rel Freq +CumFreq
Model Output of Interest
• Yield from Direct Flow Rights
-Silver Lake DF Rights
-Barker Reservoir DF Rights
- CBT Used Direct Flow
-CBT Used by Exchange (directly into WTP)
- Farmers Ditch Shares
Model Output
• Water withdrawn from Storage
-Silver Lake Watershed
- Barker Reservoir
-Boulder Reservoir
Max Storage contents at end of June
• Boulder's share of CBT system storage
Classification of Years (for this example)
• Average
- Average of 285 year study period
• Dry
-Year with a storage index of 0.8 (Stage 1)
- E.g. 1892
• Drier Year
- Storage index= 0.6
- E.g. 1891
• Very Dry Year
- Storage Index 0.44 (driest in study period)
- E.g. 1888
- Note that the two most severe drought years came in years 4
and 5 of a nine year drought.
Boulder Creek Watershed treamflows
160,000
140,000
120,000
100,000
li 80,000
60,000
40,000
20,040
0
Average Max Min
00rodell 57,006 137,337 18,617
■ fiver Lake Inflow 20,318 43,224 8,397
o Barker I of law 41,274 88,854 16,512
Direct Flow Yields
1 o.oao
9.000 Direct Flow Rights and
Farmers Ditch are
Relatively Senior -
7.000 - Little Reductan in
Yield in Stage 1 Dry
Year
6.000
5.000
4.000-
3.000
2.000
1.000 -
SL Bark EX Farm CBT
13Average Year 8,502 3.019 1,554 1.797 4.699
■ Dry Year 1891 8.666 3.051 580 1.948 1.006
OVery Dry Year 1888 7.460 977 360 859 1.041
Yields from Storage
8,000
7,000
6,000
5,000
4,000
3,000
2,000
I
1,000
SL Bark BldrF es
®Aver:age Year 723 2,343 5,998
■ Dry Year 1891 1,966 4,327 6,771
OVery Dry Year 18881 2,532 2,670 l 61,998
Results from Storage Index
(0.85 trigger)
Drought Index Summary
Total Years 285 Prob Interval
Drought Index Years 27 9% 11
Freq of Level 2 24 8% 12
Freq of Level 3 3 1% 95
Freq of Level 4 0 0%
Largest Shortage 5838 of
Longest Drought 9 yrs
Results from shortages
Shortage Summary
Total Years 2851Prob Interval
Shortage Years 14 5% 20
Freq of Level 2 7 2% 41
Freq of Level 3 3 1% 95
Freq of Level 4 0 0%
Largest Shortage 5838 of
Longest Drought 9 yrs
Observations and Conslusions
• Interruptible In-stream flow right on North Boulder Creek
is never recalled
• All Farmers Ditch water is used at BRWTF every year
• The worst shortages occurred in latter years of multi-
year droughts.
• CBT limit in dry year is ~ 1,000 of direct + 7,000 of from
storage.
• Storage Index triggers too many false alarms at stage 2;
consider returning stage 2 to 0.8 rather than 0.85
• Based on predicted shortages the system is at its
reliability limit at a demand of 28,599 of (as operated)
• Overall, the oracle is pretty good, but WRAB must ask
the right questions.
Additional Data/ Analysis for Consideration
• Include the 450 year record and climate change
scenarios as comparisons.
- Compare historical data including 2002 as a comparison to tree-
ring reconstructed and climate change flows
• Include capability to allow demands to vary with weather
conditions, e.g.; provide for greater demands during
some of the drier years.
• Provide disaggregated data on Windy Gap deliveries
and use
• Operations at 3 demand levels (low, current build out,
high enough to get maximum yields of all rights.)
• Include a hypothetical scenario allowing CBT carryover
per current policy
• Discuss impacts on yields if Carter Lake pipeline is
constructed and Boulder Reservoir no longer used for
delivery to BRWTF, but available only for CBT exchange
to ag users