Water Availability Research

[glenncampagna]

• We will compile research related to existing water availability calculations in this issue which will be used to accomplish goals in #818

  Sources:

• JK: This paper defines water availability as the following: https://iopscience.iop.org/article/10.1088/1755-1315/106/1/012073/pdf
  • $WA = QNSF - ST - CU - IS$
    • Where, $WA$= the water available, $QNSF$= the 80-percent exceedance natural stream flow at a specified point on the stream, $ST$= Storage in or from the stream and its tributaries upstream from the specified point, $CU$= Consumptive uses from the stream and its tributaries upstream from the specified point, $IS$ = In-stream flow demands for a stream reach that includes the specified point.
  • "Water availability...is storage" - a sum of available surface water and groundwater
    • consumptive uses (CU), instream demands (IS), and existing storage (ST) are subtracted from the QNSF flow to calculate WA because "the outflow rate increases as the amount of storage increases" and " Water in the hydrologic cycle is always in motion and always in storage, and any hydrologic control volume represents storage."
• Determining Surface Water Availability in Oregon :
  • Identifies the same water availability equation w/ the same var definitions laid out in JK's source (page 1):
  • $WA = QNSF - ST - CU - IS$
  • This version of water availability is defined by Oregon as the difference between natural stream flow and the sum of in-stream water rights and out-of-stream consumptive uses (which doesn't explicitly mention storage). Meaning this definition of water availability, and that from the source w/ the same eqn above, only accounts for the total flow of water, and not aquatic life or waste assimilation
  • Uncertainty & error considerations are also mentioned on page 56
• Texas Water Availability Model (WAM)
  • More info and evaluation in an article/paper here
  • Related: water availability modeling with WRAP , which WAM consists of
• Georgia State Water Plan's definition
  • Defines availability as the water that can be used/withdrawn without substantially altering the desired hydrologic flow regime and the opportunities for use of water supported by that flow regime. This definition seems broader than only referring to the available volume of water, and might include ecosystem services and/or waste assimilation underneath "opportunities for use of water supported by that flow regime"
  • This is model-based, and inputs are: "the desired flow of the river system, expected return of treated wastewater to the system, the desired water supply, and the desired reliability of the water supply"

[megpritch]

Pennsylvania

• Susquehanna River Basin Commission (SRBC)
  • "WATER AVAILABILITY is defined as the hydrologic capacity of a water source or watershed to sustain additional water demands after considering current water uses and water conditions." - Global Environmental Management Initiative, 2012
  • WA = WC - CU , where water availability (WA) is the remaining water after subtracting consumptive use (CU) from the calculated water capacity (WC)
  • Calculated water capacity (WC) is the available capacity of a watershed, calculated using low flow margin method:
    • WC is equal to 50% of the 10-year baseflow, minus the September P75/P95 flow; where the September P75/P95 flow is decided to be the minimal quantity of streamflow needed to provide protection of the stream ecosystem during low flow conditions
      • WC = 1/2*[10-yr baseflow] - [min flow for ecosystem health]
    • Thus, $WA = 1/2[$ 10-yr baseflow $] - [$ min flow for ecosystem health* $] - CU$

New Jersey

• NJ Water Supply Plan 2017-2022
  • NJ doesn't categorize sources by surface water and groundwater when calculating water availability, instead:
    1. Surface-water reservoirs (with a defined safe yield)
       • water availability from this source type is in terms of "safe yield"
       • safe yield = "the volume of water the reservoir system can supply during a repeat of the driest conditions yet experienced" (pdf p.16; web view p.25)
       • safe yield is used as the limit for what can be permitted
       • safe yield is a function of a reservoir's inflows, the infrastructure available to store and transmit that water, and the operating rules which govern reservoir operation
    2. Stream and river surface intakes and unconfined aquifers (aka water-table systems)
       • groundwater aquifers interact with the surface waters above them
       • water availability is determined using low flow margin (LFM) approach (usually at the HUC11 level) to calculate amount of water that can be sustainably withdrawn without considerable damage to the ecosystem (pdf p.19; web p.28)
       • appears that the LFM method is virtually the same as the one referenced above from SRBC
    3. Confined aquifers
       • mostly coastal-- "separated from the surface by one or more geologic units that hinder the vertical movement of water"; important potable water source for the region, but can be affected by saltwater intrusion
       • says water availability here is a function of aquifer extent, groundwater divides, and critical area boundaries (footnote 4)
• NJ WSP Appendix A
  • Breakdown of source type characterization and water availability by water management area (WMA)

South Carolina

• Impact of Uncertainty in Pool Evaporation Estimates on Water-Availability Models
  • Compares the results of four different evaporation calculation methods across multiple reservoirs
  • "The observed uncertainty in water-availability predictions is a direct result of the uncertainty in evaporation estimates. Under normal flow conditions, the uncertainty is small due to an abundance of water. As a result, any one of the four evaporation methods used in this paper performs well in evaluating water availability. However, under drought conditions, the uncertainty in evaporation estimates caused significant uncertainty in the total available water. Increased water consumption from industry and population growth intensifies this effect. The uncertainty in water availability was estimated to increase substantially with future increases in water consumption."
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