Preliminary Analysis of Projected Water Demands

R. W. Buddemeier and B. B. Wilson


Rate of Demand Increase, PWS Groups
Year of Projected Shortfall, PWS Groups
Volume of Projected Shortfall, PWS Groups
Composite Risk Index (Rate, Year, Volume), PWS Groups
Composite Risk Index (Rate, Year, Group), Aggregated at County Level
SW Kansas: A Special Circumstance
Primary and Secondary Suppliers
Risks associated with inadequate water supplies and unmet demands include:

1.  Increased costs, limits on economic development
2.  Local and regional competition for limited supplies
3.  Dependence on marginal supplies decreases reliability, increases vulnerability
4.  Diminished quality of life
Among the contractual objectives of the High Plains Aquifer Evaluation Project is technical support to KWO in meeting the Legislature's mandate to the KWA to provide recommendations "...related to the potential for competing water needs for at least the next 20 years and the means of addressing the competition."

As a result of discussions with legislators and agency heads, this mandate has been formulated in terms of evaluating the means by which projected public water supply demands for additional water by the year 2020 might be met. As this activity has not previously been undertaken, methods have had to be developed. Since the topic is a complex one and the time and resources available do not permit a detailed, across-the-board analysis of all public water suppliers (close to 1,000 in the state), the strategy adopted has been one of 'triage' -- a term originally used to describe prioritization of care for casualties in warfare or disaster situations, but more generally applied to dealing with a wide range of problems with limited resources (see appendix for further discussion of this approach).

Because of the emphasis on competition, the project has focused on identifying the locations most likely to experience difficulty in meeting future demands as a result of mismatch between demand and available resources. KWO public water supply demand projections were used as the basis for the assessment. The initial assessment is designed in three hierarchical stages:

1. Rank the absolute amounts and relative rates of demand change in various geographic areas, and select criteria by which to make a first identification of potential problem areas.

2. Review the classifications and refine with additional criteria as appropriate -- water quality is an example of a consideration in obtaining an adequate usable supply of water in some areas.

3. Assess the water potentially available in the identified areas from:

a. Lakes, impoundments, and reservoirs (KWO)

b. Streamflow and alluvial aquifers (KGS, KWO)

c. Groundwater (KGS).

Once complete, this initial assessment will have identified the areas most likely to experience difficulty in obtaining adequate water in the future, and will also provide an inventory of the candidate sources -- and the competitors for their use -- in the same area. At this point, a more detailed analysis can be undertaken to address possible resolution of the anticipated problems.


The KWO projections tabulate demand for the years 2000, 2010, 2020, 2030, and 2040 by each public water supply, broken down by county. Because the defined boundaries are subject to change (e.g., by annexation, merger, formation of new districts, etc.), and because there are extensive transfers of water between suppliers, it is doubtful whether present-day maps of the service regions and projected demands of the individual suppliers and a 20-year analysis based on present distribution of supply would provide a reliable planning basis. For these and other reasons, the initial assessments are made primarily at the level of district 'groups' that are known to be linked by contracts or transfer agreements. Additional analyses were carried out at the county level as well as by individual district,

Analysis at a scale above that of the individual supply district has a number of advantages and justifications:

The 2000, 2010, 2020, 2030, and 2040 projections for each supplier in a group were summed to give a total, in thousands of gallons per year. The net changes and percentage changes in demand were calculated for each group, and the results tabulated and mapped in ArcView. Individual suppliers were classified as primary (possessors of surface or groundwater rights or long-term reservoir contracts) secondary (with no water rights, obtaining water through primary suppliers). The supply and demand projections for the groups were also apportioned at the county level.

Preliminary criteria were developed to conduct the triage. Three primary factors and a secondary factor were considered. First, projected shortfalls in supply (present supply minus projected demand) were analyzed, and ranked by year. Because of the time required for both legal and engineering solutions to problems to be implemented, near-term problems have a high level of urgency. Second, it was judged that there was some absolute level of increase that was sufficiently small to be unlikely to result in serious problems unless the supply were already extremely marginal. An initial threshold was established and the amount of demand shortfall was classified above in steps above this level. The values selected can be easily changed if review suggests better values. The third factor considered was the percentage change. It is common experience that relatively straightforward conservation measures can result in savings of 10% or more unless the community in question has already been under heavy restrictions, and a 20 year time frame is ample to allow for the institution of education, regulation, and pricing programs to increase use efficiency. Increases of less than 10%, regardless of absolute size, were not considered likely to be highly problematic. Increases of 10-25% and >25% were ranked as increasingly serious.

The secondary factor considered is actually more appropriate to the supply issues discussed elsewhere in this report, but was included here to highlight a separate class of problems. This assessment implicitly assumes that present supply is adequate and stable. This is not always the case; in particular, substantial areas of the High Plains aquifer have projected depletion times of less than 50 years, and the public supplies relying on those resources have few alternatives to turn to. The problem is even more serious for communities with growing demands in those areas where the aquifer is administratively closed to further appropriations. Southwest Kansas was used as a case study of these problems, and also serves to illustrate the display issues involved in comparing districts, groups, and counties of disparate size and demand density (see below).


Rate of Demand Increase: Assessed for all groups of water suppliers, whether or not they have water rights or contracts adequate to meet projected demands. The Year 2020 is used as a standard base for comparison.
Figure 1:  Percent Increase in Demand, 2000 - 2020
20 year growth (all documented suppliers) Risk Factors: Rate of Demand Growth
  < 0 %
1.  Rapid or extended growth may overtax infrastructure 

2.  Supply reliability may be lower at higher delivery rates or volumes
3.  Regional clusters of growth set the stage for competition when some districts exceed their supply
4. Reduction of common reserves increases large-scale vulnerability  
  0 - 10 %
  10 - 25 %
  > 25 %

Year of projected shortfall: Assessed for those districts whose demand will exceed present firm supply by or before 2040.
Figure 2:  Projected Time of Supply Shortfall
shortfall year  Risk Factors: Time of shortfall
  > 2040 Rapid onset of problems:
1.  Limits options for response
2.  Promotes high-cost, short-term, 'band-aid' solutions
3.  Puts a premium on effective planning and preparation

Volume of projected shortfall for those groups with shortfalls in the year 2020. Use of 2040 shortfalls would show more areas and larger numbers.
Figure 3:  Projected Shortfall Volume, 2020
shortfall volume, 2020 (kgal/year) Risk Factors: Shortfall volume
  < 0 (0) The following increase with increasing volume of projected shortfall:
1.  Resources at risk  -- people, dollars.
2.  Time required for correction
2.  Cost of correction
3.  Sensitivity to errors in estimates
  0 - 25,000 (3)
  25-50,000 (2)
  > 50,000 (1)

Composite Risk Score: Sum of rankings in the year, rate and volume classes. For this application the rate and volume classes were calculated on the year of shortfall, not a standard time.
Figure 4a:  Composite Risk Score (shortfall groups) -- Time, Volume, Rate

score (sum of volume, percent and year) Risk Factors: 
   no shortfall through 2040 Risks and costs of correction or mitigation are related to the magnitude of the problem, the time available to deal with it, and the rates of change and uncertainties involved.  The simple sum of component scores is one example of a combined approach.

Composite Risk reallocated at the county level -- calculations and scoring are similar to the Group analysis, but class values were adjusted for the scale difference.
Figure 4b:  Composite Risk Score (shortfall groups by county) -- Time, Volume, Rate

score (sum of volume, percent and year) Note: 
   no shortfall through 2040 In order to provide comparable displays at the different scale of the counties, scoring criteria were adjusted as follows:
Percent Growth by 2040: same as PWS districts
Shortfall year: 2020 = 1, 2030 = 2, 2040 = 3
Shortfall volume: >200,000 kgal/yr = 1, 100,000 - 200,000 = 2; 0 - 100,000 = 3

SW Kansas Municipalities -- a special case study in isolation and resource access. Color coding by year of shortfall.
Figure 5a:  A Special Case -- SW Kansas Suppliers' Demand Projections

shortfall year  Special Risk Factors
  > 2040 Identified districts:
1.  Are mostly in areas closed to appropriation;
2.  Are isolated;
3.  Depend on a resource that is depleting;
4.  In many cases, are on the margin of the aquifer;
5.  Lack supply alternatives.

Figure 5b:  A Special Case -- SW Kansas Groundwater Supplies

Primary water right holders -- the Group supply does not reflect that of all its members.
Figure 6:  Primary and Secondary Water Suppliers
Primary water right holders Risk Factors: Secondary suppliers
  Possess some groundwater or surface water rights or long-term reservoir contracts 1. Planning and development is effectively under the control of the primary supplier(s).
2. Competition and shortfalls may develop within supply groups that have adequate total resources on paper.
  No rights or independent contracts; depend on purchase from primary suppliers


Funded (in part) by the Kansas Water Plan Fund