NID Board of Directors Accepts Water Planning Projections – Looks to Future Planning Efforts to Continue Dialogue

November 18, 2020

The Nevada Irrigation Board of Directors received a presentation from staff and its consultant, HDR, regarding how the Water Planning Projections were developed. The focus of the presentation was on how the model made predictions about NID’s water supply and future demand and what assumptions were used in the development of the Technical Memoranda.

Having received a number of comments from the public on the Water Planning Projections, the staff stressed that the model, used to produce the Technical Memorandum, is a dynamic tool with assumptions that can be changed or updated when new planning efforts are undertaken. It is expected that the next planning effort will be the Urban and Agricultural Water Management Plans required by the State to be submitted next year.

The District’s mission is to provide a dependable, quality water supply; continue to be good stewards of the watersheds, while conserving the available resources in our care.

In keeping with its mission, NID is committed to using best practices and good stewardship as it seeks to understand future water supply conditions and customer demand. Projecting future conditions is a dynamic process and the models used will be updated on a regular basis to reflect trends, constraints, and needs as it relates to the District’s service area, infrastructure, and policies.



NID Postpones October 28 Water Planning Projections Board Workshop

October 21, 2020

 (Grass Valley, CA October 21, 2020) – The Nevada Irrigation District (NID) today announced that it has postponed the October 28 Board Workshop on its Water Planning Projections to a future Board Meeting. The public comment period, originally scheduled to end on October 9, 2020, was twice extended to accommodate stakeholder requests and ended on October 19, 2020.

The Board agenda item has been postponed to give the District adequate time to review the large volume of comments received and prepare for a future Board meeting.

The recently released 2020 Water Planning Projections will be used by the District in part to prepare a number of reports such as the Urban Water Management Plan and the Agricultural Management Plan, both required by the State of California to be submitted every five years and are due in 2021.

Water Planning Projections – Responses to All Questions Provided by the Public with Answers

October 6, 2020

Q1. Why is it that none of the upper division dams, conveyances and reservoirs are mentioned in the Water Demand Model? What about environmental demand in the upper division?

A1. The upper division facilities are supply facilities and don’t have customers that consume water. As a result, these facilities are not included in the Demand TM. You will find them in the Supply TM. The environmental demand is included in the Demand TM and is summarized in that document on page 25.

Q2. According to the Dept. of Finance Regional Census Data, (cited in the report), Nevada County had a loss of 650 people during the last decade.  Since 80% of the District is within Nevada County, (4 of the 5 Divisions), that had a net loss of population over the last decade, why does the model project raw water demand increases of 44% over 40 years for the Deer Creek System and 36% increase for the Bear River System?  The factors leading to these outcomes and the weight given to each factor need to be specifically listed and clearly explained.

A2. Population projections are just one of the components of the demand factor. NID agrees that general population projections for the Nevada County portion of the District are relatively flat. However, NID’s demand factors also look at new hook ups from existing parcels, which are growing, for example between 2000-2020 NID has added 3,329 new connections. Capital improvements on “moratorium” canals also add additional capacity and customer use.  In addition, the model takes into account the potential for feasible future service areas (soft service areas).

Q3. How do you justify the validity of using soft service areas, canal capacity, parcel data, and arable land base to determine future need when we live in such unpredictable times with pandemic caused economic recession, catastrophic wildfires, rolling blackouts, and public safety power shut offs?  We cannot count on business as usual for total “potential demand” How does NID account for these significant and unpredictable future events?  What weight do you give this complicated and increasingly baseless estimate?

A3.  The Nevada Irrigation District views the Water Planning Projections as a long term planning tool built to look at long term trends. It is not intended to address short term impacts such as those mentioned above.

It is important to note however, the model is a living document and is adjustable.  If NID finds a new trend that becomes important for long term planning, the model can be adjusted to consider new assumptions.

Q4. The minimum environmental flows below Rollins Dam are captured by Combie Reservoir. Why are these flows considered lost to the system?

A4. The flows below Rollins are captured by Combie and reused by NID so they are not considered lost to system. The flows below Combie are lost to District and included in the environmental flow calculation.

Q5. Where is the data demonstrating how much, where, and why the environmental flows are lost to the system?

A5. NID tabulates the amount of the environmental flow requirement that is unrecoverable. Locations include Middle Yuba below Milton diversion, Wilson Creek below Wilson Creek diversion, Canyon Creek below the Bowman Spaulding diversion, Texas Creek below the diversion, Clear Creek below the diversion, Fall Creek below diversion, Trap Creek below diversion, Rucker Creek below diversion, Bear River below Lake Combie, and Deer Creek below Scotts Flat.

Q6. When talking about the agreed upon environmental flows, it says “These minimum flows are not recovered and, therefore, factored into demand estimations.” The Water Supply Memo Table 3-1 notes the environmental flow requirement again. Is this subtracted again to determine the shortage?

A6. Yes, it is.  In the table you reference, the environmental flows have been backed out of the demand, so there is no double counting

Q7. Looking at P7 – 3rd paragraph under Section 4.2 Why didn’t we compare the last 10 years of actual data to the projected to confirm if the trend supports the correlation of these two single data points from 13 and 18 years ago?

A7. Looking at the Demand TM section 4.2 – this section summarizes the model used in 2011 update. The current update also includes the last ten years with the several dry years that occurred.  NID also looks at growth projections and the land use trends and how they affect the overall trends. Because NID works with assumptions in the model, the number would not necessarily correlate. This is why a high and low bracket is developed, so we can capture those scenarios.

Q8. Looking at Demand TM, Page 11 – 1st paragraph, how much water is associated with the PG&E and CDFW contracts?

A8. The PGE contract is a supply contract and the amount of water available in the agreement is variable, and based on current year hydrology. The maximum amount of water available from PG&E is 54,000 acre-feet however, a full allotment of water is rarely available. The California Department of Fish & Wildlife (CDFW) agreement stems from the acquisition of water rights for the development of the 1963 Hydroelectric Division, and include instream flow requirements. The environmental flows lost to the District include a minimum of 7,700 acre feet.

Q9.  Demand TM, page 25 (4th paragraph) –Clarify if average flow or peak flow values are included in the Total Demand value.

A9.  Both are calculated. Peak flows are used in future planning for infrastructure, such as conveyance systems, to size for future demand. The average flow is used to derive the total system demand and evaluate the adequacy of our existing supply. Average is used in the total demand value.

Q10. In the water demand projection model figure 3-3 shows dramatic population increases for Placer County. Did this analysis separate out the NID District boundaries from the County?

A10. The data was not broken out that way, rather we looked at zoning within the District by parcel not at county population growth in the Placer portion of NID.

Q11. What is the population growth in the NID portion of the County?

A11. The data was not broken out that way, rather we looked at zoning within the District by parcel not at county population growth in the Placer portion of NID.

Q12. What is the raw water projected demand in the NID portion of Placer County?

A12. The data was not broken out that way, rather we looked at zoning within the District by parcel not at county population growth in the Placer portion of NID.

Q13. Does the TM assume any expansion of NID service area in Placer County between2020-2060?

A13. It does assume some growth in the “soft service areas,” parcels within the District that may request water service from NID in the future, but it does not consider any changes to NID’s District boundary.

Q14. In the water demand projection model update table 6-3 shows a 10% increase in annual demand for every decade. According to NID records the actual demand from 2008 to 2017 decreased by 15%. Why and how do you arrive at a 10% per decade increase over the next 40 years?

A14. Looking at the Demand TM, Table 6-3 does show a ten percent increase. There is not a historical decrease in total demand. There is a decrease in potable water demand which is small component of the overall demand. Historically, there has been an overall increase in total demand driven by existing residents adding connections and greater use of raw water for irrigation purposes.  Nearly 85% of NID’s deliveries are raw water, for irrigation use, so the demand numbers are not driven simply by population changes.

Q15. Why are there inconsistencies regarding the number of years projected in the various tables?  Many projections are to the year 2060 and others are to the year 2070. There should be consistency.

A15. The NID numbers are consistent with census figures and the Dept. of Finance projections which go out to 2060.  The NID Board has asked to see projections out 50 years, to 2070.

Q16. Referring to the “objective” stated in the Demand TM, at the top of page 8, “consistency with previous water planning assumptions, but incorporating new regulations and climate change impacts,” please describe whether this means that the present TM uses the same assumptions regarding the rate of demand increase that NID’s consultants used in previous demand analyses in 2005 and 2011, except for new regulations and climate change impacts. If there are other differences in the methodology of the 2020 demand projections and those in the previous analyses, please describe them.

A16. There was no change to the methodology. The model has merely been updated with ten years of actual usage, the new Dept. of Finance growth projections, and the County land-use projections. NID has also incorporated the new environmental flow requirements from the FERC permitting process. These inputs will change the trends but not methodology.

Q17.  In the Water Supply TM, Please describe which of the figures in Table 3-1 are modeled and which of them are calculated; if calculated, please describe the data sources and process of developing the calculations.

A17. In table 3-1 is the summary of 2070 five year drought water supply. It begins by summing up incremental supply sources. Then it sums up demand (the environmental flow and customer demand). Based on mass balance, it calculates both the updated carry over storage and shortages that result from the difference between supply and demand.

The only modeled number is the available carryover storage in the averaged year which is the starting condition in year one. Based on the reservoir operations model with the 2070 median hydrology, the updated 2060 demands, and the projected FERC environmental flows, we ran that for years 2006-2011. The carryover storage is what remained on 10 /15 for each year of model, the values were averaged together getting to the 7,500 number, the initial starting carryover storage for analysis.

Essentially in each year, the total supply is calculated and then based on the drought management plan, the demand is reduced according to the Drought Management Plan, action stages.  The demand is reduced (except the environmental flows because they are fixed). Mass balance is then calculated in each year and updates the resulting carrying over storage based on previous years’ supply and demand.

Q18. Please explain the meaning of the phrase “per NID water rights” in footnote 1 to Table 3-1. Does this mean that the table shows only the Watershed Runoff minus the amount to which PG&E has water rights or first call? Does it assume that PG&E water rights for power generation have priority over NID rights for water supply? If other, please explain.

A18. It is referencing that most of NID’s water rights have a time period when NID can divert or store water. The average historical run off calculation took those collection periods into account to ensure NID is not taking water that was not collectable per our water rights. This watershed information is described in the Water Supply TM, 2.1

Q19. Please explain the rule curves used in the modeling that govern carryover storage for each of the NID storage reservoirs.

A19. For the reservoir operations model in Res-sim, conservation curves were used in each of the reservoirs developed for FERC relicensing, and those have not changed. For Table 3-1, the conservation curves don’t apply to the analysis. It was strictly a mass balance analysis to determine the difference between supply and demand to update the carryover storage from year one to year two and so on….

Q20. On page 11, the required flows are listed as 27,900 and 58,800 cfs. I think they should be 27,900 and 58,800 acre-feet per year.

A20. Yes, it should be acre-feet per year.  This has been corrected in the document.

Q21. Demand TM, on page 22, the text mentions six NID treatment plants, and Figure 5-9 shows 7 NID treatment plants. How many water treatment plants are there?

A21. During the time period of data referenced in the TM’s, NID had 7 water treatment plants. In 2016, NID consolidated Cascade Shores into the Elizabeth George water treatment plant. We now have six water treatment plants.  When eight treatment plants are mentioned in the document, it is referencing the Grass Valley and Nevada City treatment plants which are supplied raw water by the District.

Q22. What was NIDs rationale for planning for drought by picking the five worst years on record, and putting them in sequence for calculating water supply projections? In other words, why did NID pick this methodology?

A22.  This work began shortly after the drought (2018) and, at the time, then Governor Brown signed an executive order requiring water suppliers to perform an analysis using five driest water years on record for the projections. The State is in the process of changing the Urban Water Management Plan and recently issued draft guidelines to require the five driest consecutive years. This is a living document and we can adjust to the new requirement.

NID has run, as requested, 2 additional Five Year Drought Alternative Analysis

Q23. In the Water Supply Memo Table 3-1, are the drought years values presented here based on using the operations modeling and with historic time series for initial conditions, or an average carryover storage going into the drought years?

A23. The only modeled value in the table is the initial condition of carryover storage based on model run of 2070, with projected demands including the new FERC requirements.

Q24. How old are the inputs? Are they still relevant to use? Figures 5-4, 5-5, 5-7, 5-8, and 5-9 in the Water Demand Technical Memorandum (Demand TM) imply that data collection and use ended in 2017.

A24. Actual use data goes through 2018 and, yes, they are current and relevant. The land-use growth is from the most recent census and Dept. of Finance projections with any recent general plan data. This is the most recent data available. The documents were developed beginning in 2018 so that is why the data stops at 2018.

Q25. Are Mutual Water Company customers and NID urban water customers being held to the same standard of conservation and drought response?

A25. Yes, NID follows the Drought Contingency Plan during times of drought and mandatory conservation. Mutual Water Companies are held to the same standard as all other raw water users. However, an exception might be if the State issues mandatory conservation measures that differ from our drought contingency plan, then the District abides by the State requirements.

Q26. How are you defining/using the term “environmental flows?”

A26. Environmental flows are regulatory required in-stream flows that can’t be recovered by the District and minimum dead pool requirements for the District reservoirs. Information is in the Demand TM, page 25.

Q27. Why is there no mention of the higher probability and frequency of flooding in the Hydrology TM, and how could this important issue be addressed in these TMs?

A27. The District is not a flood agency.  We operate our reservoirs for water supply not flood control. The TM’s are focused on demand and supply and not focused on flooding conditions. However, by modeling the carryover storage with the Res-sim model, we somewhat capture the change of reservoirs conditions as a result of climate change.  It shows run-off with more spikes and those spikes occurring earlier in the year. That does have an impact in carryover storage.

Q28.  How do the various consumption factors interact: Is it applied water based on crop type and irrigated acreage v. canal flow data v. consumption values obtained from customer billings.

A28. Yes, NID looks at all of these demand factors and breaks them into raw water demand based on evaluation on canal gages, crop survey report, losses, total acreage, current land uses, and future demand. The other big category is treated water. This is pulled from actual customer billing plus Mutual Water Companies, treatment plants, loses, and per customer demand. In the model each is kept separate so high and low scenarios can be observed. NID can see how sensitive the changes are. Changes may interact on timing so we pull out winter usage from summer usage.

Q29. How do you validate the model projecting out to 2060 based on 2018 baseline? You should go back to 2007 data and apply your model, see how looks.

A29. The model does not begin with a baseline of 2018. It looks at all of the data from the last two updates and added 2007-2018. When all the data is incorporated there is a trend line. Long term projections are more likely to be a straight line vs. peaks and valleys. The model contemplates highs and lows to get a range in order to project the future conditions. 

The model is a long-term trend projection tool and is not meant to predict discrete outcomes under multi-variable temporal inputs.  It is similar to climate change modeling that is used to project long-term trends, but not used do predict tomorrow’s weather.  Peaks and valleys are visible over short periods of time but hard to predict into the future. Over the long term, peaks and valleys flatten and one would expect to see a straight line.

Q30. Unsatisfied with demand of 1% per year. How did you get to 1% when Nevada County population is flat?

A30. The overall demand shows an increasing trend. Customer growth is not directly proportional to population growth.  NID annual customer account growth has increased an average of 0.2% (raw water customers) and 0.8% (treated water customers) over the last 20 years.  Customer growth can occur when existing homes/residents connect to the system for a variety of reasons.  Unit water demands are applied to each customer connection to calculate projected demands. Reduction in unit water demands can be the result of conservation programs the District may select as part of a suite of alternatives identified in the Plan for Water process.

Q31. How are you using General Plan data on Deer Creek watershed? Are Deer Creek flows below Scotts Flat lost?

A31. The model incorporated projected land-use data and overlaid GIS data base for demand types within that area.  Flows in Deer Creek below Scotts Flat are imported by the District for re-diversion to the Newtown, Tunnel, and Keystone Canals. Flows beyond Lake Wildwood reservoir are lost to the District.

Q32. Demand question number 10 re: growth. Census, Dept. of Finance, General plan data, and last urban water management plan. When you used 2015 UWMP assumptions, how were they used?

A32. The original individual growth parameters from the 2011 Raw Water Master Plan were used as a starting point for each of the service areas within the NID system.  The County General Plans were reviewed to determine if it was appropriate to adjust based on land use, and various sources of population and growth projections were reviewed to determine if the growth projections should be adjusted.  The review of censes, Dept. of Finance, General Plan, and UWMP data was subjective. 

Q33. NID ran scenarios that did not consider conservation alternatives that could be done in Ag sector, some that have been showed in other districts and countries that could realize significant savings.

A33. Conservation, demand management, and other demand reducing policies are a water resources planning alternative strategy to be evaluated and compared to other alternatives in the future Plan for Water process. The supply projection did take into account reductions of 40 to 50% during drought and is a form of conservation.

Q34. Why are the PGE storage lakes a loss to the District? 

A34. Bowman/Spaulding canal is an NID conveyance so minimum flows are NID’s responsibility.

Q35. Where do I find minimum inflow streams?

A35. Some of NID’s instream flows are part of the 1963 Hydroelectric water rights and are attached to those filings. Future instream flows are a result of FERC relicensing negotiations, and can be found in those documents.  Deer Creek instream flows are part of an ongoing water rights process and have not been finalized, however preliminary targets have been included in the model.

Q36. Will NID utilize the Water Budget model put out by State DWR?

A36. District will adhere to the Water Budget as it is required for the UWMP. During the UWMP update, NID and consultants will be incorporating data from the model to complete the update.

NID’s existing planning processes, and specifically the hydrology, supply, and demand analysis already include many of the approaches and methodologies listed in the Draft DWR Handbook for Water Budget Development.  As identified in the Handbook, the extent of the analysis is a local decision based on the district’s needs, capacity, and available resources. 

Q37. On page 19, figures 5-6, and 5-7, raw water sales are only shown for 5 years and increased 2.5% while demand per customer decreased 40%.  What is the long term conservation target for raw water use?

A37. This is a policy related question and should be addressed as a Board-directed target through the Plan for Water and associated policies.  As mentioned before, the model is intended for dynamic use and expected to be updated annually as conditions, policy, and technology changes.

Conservation, demand management, and other demand reducing policies are a water resources planning alternative strategy to be evaluated and compared to other alternatives in the future Plan for Water process. 

Q38. According to figure 5-7, page 21, potable water use dropped by 26% even though the number of customers increased by 7%.  What is the long term conservation target for treated water?

A38. This is a policy related question and should be addressed as a Board-directed target through the Plan for Water and associated policies.  As mentioned before, the model is intended for dynamic use and expected to be updated annually as conditions, policy, and technology changes.

Conservation, demand management, and other demand reducing policies are a water resources planning alternative strategy to be evaluated and compared to other alternatives in the future Plan for Water process.  Additionally, the District will incorporate future conservation mandates developed by the state and incorporate them into the model.

Q39. Why is there only 5 years of raw water data shown while there is 10 years of potable water data shown?  How then can these be compared?

A39. Canal/gage data entry is a time consuming and costly exercise (thousands of data points).  After it was decided that the 2011 model would be used, the direction was to focus on the 2012 to 2018 raw water data since that captured recent dry years.  The dry year comparison (2012 to 2018) is still valid.

I don’t know, but it would be helpful to show 20-30 years of #customers and AFY demand for raw, treated, and wholesale/mutual customers.

Q40. Where is an environmental water management plan and why has the environmental demand been limited to 2 paragraphs in this update when environmental water demand is the majority of the natural flow? 

A40. The District does not have an “environmental water management plan”.  Environmental Flows are established by regulation are their own “management plan”. They include the volume of water based upon the water year type, and the timing of flows. The District is required to follow this plan.

Q41. Why doesn’t NID use the Handbook for Water Budget Development format for the Raw Water Master Plan when both the upcoming Ag Water Management Plan and Urban Water Management Plans will require this format? 

A41. The District is currently in the process of updating the UWMP and the AWMP and will follow the state’s guidelines and format as appropriate.  When the District begins engaging in updating the Plan for Water, it will assess the appropriate format to use.  Recall, the RWMP is a District-developed plan, and not required by state guidelines or format however it may decide to utilize the states Handbook for Water Budget Development format if it is appropriate. 

NID’s existing planning processes, and specifically the hydrology, supply, and demand analysis already include many of the approaches and methodologies listed in the Draft DWR Handbook for Water Budget Development.  As identified in the Handbook, the extent of the analysis is a local decision based on the district’s needs, capacity, and available resources. 

Q42. Where is the groundwater demand addressed given the majority of residents in the District depend on wells and groundwater?

A42. NID’s water rights and the entire NID system is based on surface water, not groundwater.  Determining the adequacy and sustainability of private groundwater wells on properties within District boundaries is not part of this analysis. 

Q43. Given that water is a finite resource, how does NID plan to curb demand?

A43. This is a policy related question and should be addressed as a Board-directed target.  As mentioned before, the model is intended for dynamic use and expected to be updated annually as conditions, policy, and technology changes.  However the model does contemplate the District drought management plan in the analysis.

Conservation, demand management, and other demand reducing policies are a water resources planning alternative strategy to be evaluated and compared to other alternatives in the future Plan for Water process. 

Q44.In the water supply analysis TM: Table 3-1 shows a total demand of 255,136 acre feet for an average year in 2070. The highest demand in table 6-3 of the “Demand” document is 208,936 AF for 2060. What is the relationship between these 2 documents? Why is there a 22% increase in demand in the “Supply” document? The demand estimates in the “Demand” document include environmental flows. The “Supply” document adds these flows again. Is there double counting of environmental flows?

A44.  There is no double counting of the environmental flows.  The supply analysis TM table 3-1 shows an average year total demand of 255,136, which is the sum of the annual system demand of 208,936 ac-ft (as identified in the demand TM table 6-3) and average year environmental flow demand of 46,200 ac-ft.

Q45. Please describe why NID did not elect to re-evaluate the rate of demand increase, other than for new regulations and climate change, with an updated methodology.

A45. The rate of demand increase was re-evaluated between the 2011 study and the 2020 study. The basic methodology remained the same, but new data was evaluated and the rate of demand increase changed between the 2011 and 2020 studies.

Conservation, demand management, and other demand reducing policies are a water resources planning alternative strategy to be evaluated and compared to other alternatives in the future Plan for Water process. 

The demand projections are considered a baseline value, using historical customer data.  In addition to alternative strategies to reduce unit water demands, it is possible future regulations will also mandate maximum allowable usage, and NID will incorporate any future restrictions as it updates its projections over time.

Q46. Please describe how the TM considers cost of water in water supply demand projections.

A46.  Cost of water is not considered in the projections.

Q47. Please discuss how the 5-year drought values was developed and used in the water demand projections.   The water supply memo says that: To simulate watershed runoff conditions for a five-year drought the five driest water years were placed back to back and ordered from wettest to driest, based on their annual runoff volume: 1994, 1987, 1988, 1976 and 1977. Can you talk about how and if this back-to-back modeling was included in the operations modeling?

A47. DWR recently released its Urban Water Management Plan draft guidebook for public review. The guidebook recommends urban water suppliers to include a water service reliability assessment for a normal year, a single dry year and a five-consecutive-year drought.  While it directs the water supplier to use the driest five-year sequence within the historical period of record, DWR will allow suppliers to characterize the five-year drought differently.  NID asked HDR to modify the 5-year drought recently developed for the Water Supply Analysis Technical Memorandum (TM), presented as Table 3-1, to use the 5-consecutive driest years in the 1976-2011 2070 Median climate change hydrologic period of record.  HDR subsequently created two alternative analysis, one using the 5-year running average watershed runoff and one using the 5-year actual watershed runoff. 

The back-to-back five year drought was not simulated in the operations model.  The calculations in Table 3-1 were developed in a spreadsheet.  The one value in Table 3-1 that is model derived is the average annual carryover storage, which was used as the initial carryover storage value going into year 1 of the five year drought.  This value is based on modeled long-term average carryover storage for water years 1976 through 2011 under projected 2070 conditions.

Q48. During relicensing.  NID and PG&E provided copies to the relicensing participants of a post-processing water delivery assessment tool called the “red blue model” (YB and DS Water Allocation Module.xlsx) which used operations model data output to help summarize water deliveries to each of NID and PCWA’s demand locations.  Is this updated tool available for this current set of scenarios?

A48. The red blue model was not used for any of the analyses included in the TMs, therefore, it is not available for the current set of scenarios.

Q49. The Hydrologic Analysis Technical Memorandum (Hydrology TM) Summary states,“[t]he optimistic WMW scenario indicates up to 148 percent of historical runoff volume in lower watersheds and the pessimistic DEW scenario reduces runoff volumes to approximately 90 percent of historical and indicates the potential for drier dry years. The median scenario indicates a slight increase over historical runoff volumes, with wetter wet years.” After taking into account all of the contributors to annual water supplies minus the average demand amounts from the Hydrology and Water Supply Analysis Technical Memorandum (Supply TM) reports, plus the Total System Demand in the Demand TM projected to 2060, the reports’ data show significant surpluses in both projected Wet and Dry years.  Is that a correct interpretation, why or why not?

A49. Watershed runoff in high elevation watershed under current conditions is predominantly snowmelt driven.  In the future under climate change, watershed runoff will be more precipitation driven, resulting in flashier runoff events resulting in more spill from reservoirs.  In addition, late spring water deliveries from high elevation reservoirs under climate change will be drawn from reservoir storage rather than snowmelt runoff.  Both of these factors contribute to reductions in reservoir carryover storage.  Projected carryover storage is expected to decrease by approximately 20,000 ac-ft, relative to historical average annual carryover storage (Table 5-16, 2012 Raw Water Master Plan).  Carryover storage is the second largest source of NID water supply (2012 Raw Water Master Plan).

One other notable difference between the Supply TM and the 2012 Raw Water Master Plan in the quantification watershed runoff.  Watershed runoff in the Supply TM includes runoff in the Bear River, and other small tributaries where NID has direct diversion rights during the irrigation season.  Previously, runoff from these watersheds were not included resulting in an underestimate of watershed runoff.  As a result, the two values of watershed runoff are not comparable.

Q50. What are the specific, numerical or other assumptions that you are putting into the models used for the Water Demand TM?

A50.  Assumptions in the water demand TM including the following; future land use (general plans), future saturation of service areas (currently cannot exceed 80% for most service areas), population growth by sub-area (department of finance, 2015 RWMP), and canal losses (~15%). These assumptions can be adjusted in the model tool.  

Q51. The water demand projection as shown in the Water Supply TM Table 6-3 shows a 10% increase in annual demand for every decade. According to NID records, the actual demand from 2008 to 2017 decreased by 15 percent. Why and how do you arrive at a 10 percent per decade increase over the next 40 years?

A51. From 2020 to 2030, the demand growth rate (without environmental flows) shown is 1.1% per year, 2030 to 2040 is 0.9% per year, 2040 to 2050 is 0.7% per year, and 2050 to 2060 is 0.7% per year as shown in Table 6-3 – less than is indicated in the question.

It is unclear which data the question is pointing to for a 15% decrease between 2008 and 2017. Potable demand has decreased under a similar time frame by about 2.3% per year as shown in Table 5-4. However, total raw water demand between 2012 and 2017 has increased about 0.8% per year (see Figure 5-4). Raw water makes up about 80% of the entire NID system. It should also be noted that there were economic factors as well as drought that impacted water demands during the 2008 to 2017 time period.

Q52. How do you justify projecting an increase in water demand from agricultural production in this region given the projected impacts from climate change? See Informational Presentation to Nevada County Planning Commission by University of California Cooperative Farm Advisors Cindy Fake and Dan Macon regarding the state of agriculture in the County, December 2019.

A52. Projections are based on existing General Plan land uses and historic water usage.  Future scenarios could increase or decrease the unit water demands of a respective land use.  Planning assumptions will be updated once changes and/or legal actions have been made to change land use, restrict water use, or further define allowable uses.

Q53. Why is there no mention of wildfire or forest management in the Hydrology TM? Shouldn’t reduced evapotranspiration from wildfire and forest management be incorporated into future run-off and supply estimates?

A53.  While studies have shown reduced evapotranspiration after biomass removal and fuels reduction following wildfire or forest management, these events and/or management practices are discrete events that are not included in the modeling due to the uncertainty of actual location and impacts.  These types of events are potential water management strategies that could be investigated in the Plan for Water process.    Hydrologic projections for 2070 unimpaired flows were derived using simulated historical and projected 2070 surface runoff and base flow from the Variable Infiltration Capacity (VIC) model (Liang et al. 1994).  The VIC model is a gridded hydrologic model that simulates land-surface-atmosphere exchanges of moisture and energy at each model grid cell.  Projected changes in evapotranspiration resulting from climate change are included.

Q54. Water Supply TM, Table 3-1, looking at environmental flow in acre feet source 1984 -1988. Don’t line up with 2-1 in same TM? Where do numbers 31,000 in environmental flows in 1991?

A54. Environmental flow requirements in Table 3-1 are based on historical Smartsville index based water year types.  Water year types were updated in February, March, April, May and June, corresponding to monthly DWR Bulletin 120 forecasts of watershed runoff. As the water year type is updated from month to month, environmental flow requirements are adjusted accordingly. Table 2.1 values are for a single water year type. Table 3-1 is representative of what the environmental flow requirements would have been if the five years occurred back to back.  The table does not capture releases above environmental flows (i.e. spills).

Q55. Table 3-1 season of diversion but talks about PGE rights to first 350??? cfs into Rollins.  Does projection back out water for PGE?

A55. Yes, it does for each of the water years.

Q56. Acre feet projection, NID demand up to 2060 is a 43% increase in acre feet? Were those numbers used here?

A56. During FERC process, the projected demand scenario was to 2062. At the time, NID RWMP was projected to 2032. So we took the 2032 data and extrapolated out to 2062.

Q57. How will the new look at groundwater change your methodology? Water lost to the system is not really lost.

A57. District is a surface water only agency. Our water rights allow for the capture and diversion of surface water only. NID water that percolates into the ground water table is no longer accessible by NID. Additionally, a majority of the Districts boundary does not fall within a recognized ground water basin. When we say lost to the system, it means the District’s supply system can’t collect and deliver that water to its customers or its other obligations.

Q58: Although three different water scenarios based upon climate change are modeled in the Hydrologic Analysis and used in the Water Supply Analysis TM, no alternative demand scenarios are modeled in the Demand Analysis. Question: Can HDR explain why there are no alternative demand scenarios in the Demand Analysis.

A58. Two demand scenarios were provided based on a range of environmental flow requirements.  Growth, loss, and saturation. Values can be adjusted to develop additional demand scenarios.





NID Hosts Water Planning Projections – Technical Clarification Public Meeting September 24 at 10:00 a.m. via Zoom

September 18, 2020

The Nevada Irrigation District (NID) today announced that it has added a Technical Clarification Public Meeting to its outreach associated with the Water Planning Projections released in August.

NID has arranged to have HDR, NID’s consultant that prepared the Hydrologic Analysis, the Water Supply Analysis, and the Demand Projection, available to answer technical clarifying questions about how the projections were developed, assumptions made and the modeling used. Questions provided in advance will be answered first and, time permitting, HDR will take additional questions from the participants during the meeting. Questions to be considered at the meeting should be submitted to: by Wednesday, September 23 at noon.

The recently released 2020 Water Planning Projections will be used by the District to prepare a number of reports such as the Urban Water Management Plan and the Agricultural Management Plan, both required by the State of California to be updated and submitted every five years. The information will also be used to prepare the District’s Plan for Water, and is considered when making decisions about capital improvements to its water delivery system.

General questions and comments on the Water Planning Projections not covered by the scope of this meeting will also be welcomed by NID and should be submitted to the District by October 12, 2020 to or by mail to: NID – Attention Water Planning Projections. 51036 W. Main Street in Grass Valley, CA. 95945

Responses to issues raised through public comment will be delivered at a Board of Directors Workshop on October 28, 2020.

September 24, 2020 – Water Planning Projections Technical Clarifications Meeting

September 16, 2020



Water Planning Projections 2020

August 26, 2020

View Water Planning Projections PowerPoint Presented at August 26 Board of Directors Meeting

Responses to All Questions Submitted by the Public with Answers

An Overview

The Nevada Irrigation District presented updated Water Planning Projections to its Board of Directors on Wednesday, August 26, 2020. Here you will find summary information as well as the Technical Memorandums (TMs) associated with each study.

The Water Planning Projections consist of three studies that analyze the hydrology, water supply and water demand that help NID determine if its water storage and delivery system will provide sufficient water to meet customer demands over time and under variable conditions.

The Water Planning Projections are used to prepare a number of planning reports such as the Urban Water Management Plan and the Agricultural Management Plan (see description below) required to be updated and submitted to the State of California every five years. The Water Planning Projections are also used to prepare the District’s Plan for Water, formerly called a Raw Water Master Plan (see descriptions below), and is considered when making decisions about capital improvements to its water storage and delivery systems.

The need to update NID’s Water Planning Projections is driven by a series of requirements and assumptions, including the new Yuba-Bear System Federal Energy Regulatory Commission (FERC) regulatory requirements, state-derived climate change data, and the state-mandated planning requirements. Together, these requirements and assumptions constitute significantly new planning assumptions and drive the need to update and revise NID’s Water Planning Projections when necessary.

To receive future communications related to Water Planning Projections, click here

About Water Planning Projections

Water Planning Projections is a term used to reference the combination of three studies that are used for District planning; a Hydrologic Analysis, Water Supply Analysis, and a Water Demand Projection (see descriptions below).

About the Hydrologic Analysis

The goal of the Hydrologic Analysis is to understand a range of outcomes based on various greenhouse gas emissions reduction scenarios and to determine the unimpaired flow, the amount of water available in the natural watershed without influence (i.e., regulation of stream flow by man-made structures such as dams or diversions). The State of California anticipates conditions under climate change to include warmer temperatures; rising sea levels; declining snowpack; more intense precipitation events; more droughts; and more area burned by wildfire. These factors, among others, will ultimately impact the amount of water available in a watershed in any given year.

The result of this analysis is the unimpaired runoff in NID’s watersheds under various climate change scenarios. This information is needed to compile the Water Supply Analysis (see below).

Additional Hydrologic Detail as Presented at August 26 Board of Directors Meeting

To read the Final Hydrologic Analysis Technical Memorandum click here.

To review the Hydrologic Analysis TM Appendices  click here

About the Water Supply Analysis

The Water Supply Analysis uses the unimpaired runoff results from the Hydrologic Analysis to determine available water supply to NID over time and under certain conditions. NID’s four main sources of water are: natural snowmelt and resulting runoff, reservoir storage carryover (unused from prior year), contract water purchases, and recycled water released by treatment plants and later diverted to NID irrigation canals.

The Water Supply Analysis has been updated to consider the impact of drought, climate change, contract purchases, and new FERC license conditions for environmental flows on its water supply system. An additional carryover storage model is also used to determine what NID reservoir storage carryover will be from year to year.

The result of this analysis is the amount of water available to NID during average and wet years, as well as during a 5-year drought scenario. It is the amount available to meet regulatory required environmental flows, customer demand for raw or irrigation water, customer demand for treated or drinking water, municipal purchases and to cover system losses.

Additional Supply Detail

Five Year Drought Alternative Analysis – as requested at Technical Clarification Meeting and for UWMP

To read the Final Water Supply Analysis Technical Memorandum click here.

About the Water Demand Projection

The Water Demand model used in this projection was adopted by the NID Board of Directors and has been consistently used to assess future water demands on NID’s water storage and delivery system. The assumptions have been updated to reflect current trends.  The five components of total water demand are: the demand for raw or irrigation water, the demand for treated or drinking water, required environmental flows, system losses, and municipal purchases. It is important to note that 85 percent of NID’s water deliveries are for raw water used for irrigation purposes.

Calculating demand is a very simple process of multiplying the projected water demand factor by the number of customers or parcel size. While the multiplication is easy, numerous assumptions are made including land-use, zoning, historical billings, treatment plant supply data, canal data – 168 gages, crop reports, and others that effectively assume a state of the NID community in 50 years. The average estimated flow for each NID system can be viewed by clicking here.

The result of this projection is a range of future customer demands for treated and raw water.

Additional Demand Factor Detail as Presented at August 26 Board of Directors Meeting

Updated Flows by Service Area Charts

To read the Final Water Demand Projection Technical Memorandum click here

Other Helpful Information

How NID Uses Water Planning Projections



Responses to questions provided for the Technical Clarification Meeting

Five Year Drought Alternative Analysis

VIDEO – September 24, 2020 – Water Planning Projections Technical Clarifications Meeting


Download Audio File