Headroom is the term used to refer to the margin between supply
and demand. Target headroom is defined as the minimum buffer that a
prudent water utility should introduce into the annual
supply-demand balance to ensure that the utility's chosen level of
service can be achieved. Available headroom is the actual
difference between water available for use and demand at any given
point in time. Where available headroom falls below target headroom
the water resource zone is considered to be in supply demand
balance deficit as it does not meet the water company’s level of
service for water resources.
Headroom uncertainty is made up of supply side and demand side
components. Supply side issues include vulnerable licences, time
limited licences, data accuracy, gradual pollution, the impact of
climate change on source yields and the uncertainty of output of
new resource developments. Demand side issues include data
accuracy, demand forecast uncertainty, the impact of climate change
on demand and the uncertain outcome from demand management
measures.
Mott MacDonald has extensive recent experience of headroom
uncertainty modelling and has developed headroom uncertainty models
using both @Risk and Crystal Ball software for a number of major UK
water companies. In particular, Mott MacDonald was responsible for
the preparation of the 2003 UKWIR headroom methodology, which is
now being used by most UK water companies and water utilities.
Recent risk based headroom analysis projects include the
following:
- UKWIR: Preparation of Headroom Uncertainty Methodology Using
Risk-based “Monte Carlo” Modelling (2003).
- United Utilities: Headroom Uncertainty Modelling for all Water
Resource Zones (2004).
- Severn Trent: Headroom Uncertainty Modelling for all Water
Resource Zones (2004).
- Thames Water: Headroom Uncertainty Modelling for all Water
Resource Zones (2004).
- Thames Water, Three Valleys Water, South East Water, Essex
& Suffolk, Sutton & East Surrey: Balance of Supply Models
Incorporating Headroom Uncertainty for Whole Thames Catchment
(2005).
- Yorkshire Water: Development of Headroom Assessment Methodology
for Smaller Resource Zones, Particularly the Dales Zone
(2006).
- Scottish Water: Headroom Assessment and Development of Headroom
Strategy for Water Resource Plan (2006).
We also have wide recent experience of modelling headroom
uncertainty as part of overall water resource zone balance of
supply models. We have used this approach for major UK water
companies including the following:
- Severn Trent: Balance of Supply Modelling for all Water
Resource Zones (2004).
- Thames Water, Three Valleys, South East Water, Essex and
Suffolk, Sutton and East Surrey: Balance of Supply Model for Whole
Thames Catchment and Outline Water Resource Strategy (2005).
- Scottish Water: Balance of Supply Modelling for the Four Firths
Area Water Strategy (2005).
- Yorkshire Water: Balance of Supply Modelling for the Dales
Water Resource Zone (2006).
- Severn Trent Water: Balance of Supply Modelling for all
Birmingham and Severn Water Resource Zones (2006).
