Civil Engineering Reference
In-Depth Information
rainfall gauges, and groundwater level monitoring bores. The required
frequency of measurement to support modelling and assessment is usually
continuous or daily for surface water. River flow measurement usually
requires the establishment of a relationship between water level and river
flow at a point (a flow rating curve). As river beds are often unstable
this relationship can be unstable also, requiring an ongoing program
of field flow measurement to check and recalibrate the rating curve. It
can be worthwhile to invest in a structure to stabilise and improve the
sensitivity of the rating curve at low flows, as shown in Figure 9.1 (see
colour plates).
Groundwater is commonly monitored on a monthly or quarterly basis,
but may need higher frequencies in some cases. Monitoring of water
extraction can be via meters on pumps, bores or channels, or where this
is not feasible through various estimation techniques such as those using
areas of crops irrigated, pump hours, etc. This information underpins
understanding how the water resource behaves, climatic analysis, water user
demand analysis, and the development of models that are able to support
decision-making.
Performance indicators for objectives often include such things as economic
outputs and ecosystem condition, with associated monitoring programmes
drawing on the broad state of the environment, economy and society
information that is published and referred to by governments for multiple
purposes. This is cost-effective, but as shown in the discussion above, their
value for evaluating water resource plans can be limited because of the diffi-
culty in separating out the effect of externalities from the effects of water
management.
For example, economic outputs from irrigated agriculture are often
greatly impacted by commodity markets, pests and diseases and farming
practices. For water resource planning there needs to be a means to
separate the effects of water resource management from other factors in
analysing fluctuations in economic output levels. One approach to doing
this is to use models that are developed to simulate water availability
and production over a period of time. Such models are used in assessing
possible management options using forecast future climate scenarios
(see Chapter 8). They can also be used with current and historic climate
data to estimate the effect of the implemented management actions
as compared to what would have occurred without them. As with all
models, the weakness is the extent that the models are able to accurately
simulate complex relationships, which varies substantially for different
circumstances.
There are a great many different schemes for the monitoring of the condition
of river and wetland ecosystems. A well-known example in Australia is the
annual monitoring of the ecosystem health of Southeast Queensland catch-
ments, undertaken by the not-for-profit Healthy Waterways organisation, as
shown in Box 9.1.
