Hydrologic Analysis - Technical Memorandum, Final Report, November 12, 2020  

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.

Water Supply - Technical Memorandum, Final Report, November 12, 2020

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

Water Demand Model - Technical Memorandum, Final Report, November 12, 202o

About the Water Demand Projection

The Water Demand Projection looks at future water demands on NID’s water storage and delivery system. 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 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 economic and demographic assumptions, regulatory and legal impacts, operational assumptions, and others that effectively assume a state of the NID community in 50 years.

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

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