A Framework for Assessing the Environmental Water Requirements of Groundwater Dependent Ecosystems

Transcription

1 A Framework for Assessing the Environmental Water Requirements of Groundwater Dependent Ecosystems

2 Introduction National framework for assessing GDE EWRs 1. Important terminology 2. Objectives of Project 3. Existing frameworks 4. LWA framework (final draft) 5. Toolbox 6. Case study

3 Terminology National framework for assessing GDE EWRs Groundwater dependent ecosystem; An ecosystem that relies either wholly or partially on groundwater to sustain its environmental function. Environmental water requirement; The water regime that is necessary to sustain an ecosystem s key ecological values. Environmental water provisions; That water provided to the environment to sustain at least the basic function of ecosystems, whilst making allowance for economic and social interests. An EWP will either be the same as, or less than, an EWR. Ecosystem function; Fundamental characteristic of ecosystems related to conditions and processes necessary for maintaining ecosystem integrity, and will include provision of such services as decomposition, nutrient cycling and production. Maintenance of biodiversity is integral to ecosystem function.

4 Objectives National framework for assessing GDE EWRs 1. establish a uniform and consistent approach to the assessment of EWRs; 2. enable repeatable and defensible decisions on the determination of EWRs that incorporate the capacity for adaptive management; 3. identify and document remaining management gaps; and 4. raise the profile of EWRs amongst water resource managers.

5 Objectives National framework for assessing GDE EWRs Types of GDEs to be addressed: Terrestrial GDEs. Wetlands. Stream baseflow systems.

6 Existing frameworks National framework for assessing GDE EWRs Clifton & Evans (2001) Identify potential GDEs Dependency analysis -Groundwater dependent elements of ecosystems - groundwater dependent elements of ecosystem - key groundwater attributes --Form form of of dependence -Key groundwater attributes Water regime within which GDEs occur -Dependent processes - dependent processes - patterns of groundwater use - water sources -Patterns of groundwater use -Water sources Assess response to altered groundwater regime Establish EWR

7 Existing frameworks National framework for assessing GDE EWRs Eamus et al (2006) Identify groundwater dependent populations or species within an ecosystem Identify degree of groundwater dependency Identify groundwater dependent processes Identify patterns of groundwater dependency Identify key groundwater attributes constraining dependency Identify changes to water regime that are "safe" Determine EWRs Identify GDE response function to altered water regime

8 Existing frameworks National framework for assessing GDE EWRs Pioneer Valley, Qld (2006) Identify study area Identify biophysical setting Identify possible GDEs Identify GDE affecting activities Establish relationship between GDEs & groundwater Assess impact of GDE affecting activities Derive EWRs for GDEs Assess impact of changed groundwater regime on GDEs Derive EWPs for GDEs

9 NATIONAL FRAMEWORK National framework for assessing GDE EWRs Two step process: 1. Setting the context. 2. Identifying processes.

10 NATIONAL FRAMEWORK National framework for assessing GDE EWRs

11 NATIONAL FRAMEWORK National framework for assessing GDE EWRs

12 NATIONAL FRAMEWORK National framework for assessing GDE EWRs Two step process: 1. Setting the context. 2. Identifying processes. Now.. You can determine EWPs.

13 Toolbox National framework for assessing GDE EWRs

14 C a s e S t u d y - Pioneer Valley, Qld National framework for assessing GDE EWRs

15 Assessing the Environmental Water Requirements of Pioneer Valley Groundwater Dependent Ecosystems

16 Introduction Pioneer Valley GDE Ecosystem Water Requirements 1. Objectives of Project 2. Types of GDEs 3. Conceptual biophysical model of Pioneer GDEs 4. EWR determination

17 Study Objectives Pioneer Valley GDE Ecosystem Water Requirements 1. Phase 1; Identify ecosystems that rely on groundwater 2. Phase 2; Develop an assessment framework for assessing GDE water requirements 3. Phase 3; Assess implications of future groundwater management strategies for GDE function

18 GDE Types Pioneer Valley GDE Ecosystem Water Requirements 1. Terrestrial & Riparian GDEs (remnant vegetation) Key groundwater attribute - LEVEL Studies; - stable isotopes - leaf water potentials & soil water potentials - sap flow - mapping Strong dependence: Corymbia clarksoniana, C. tessalaris, Melaleuca leucadendra, Macaranga tanarius Limited dependence; E. platyphylla, Lophostomen suaveolens

19 GDE Types Pioneer Valley GDE Ecosystem Water Requirements 2. Baseflow GDEs (instream) Key groundwater attribute - FLUX Studies; - major ions Rn - stable isotopes - baseflow separation - (groundwater) Rainfall hydraulic gradients Baseflow Index - mapping Water Elevation (m AHD) Rainfall (mm/month) Gauge Board Bore Water Elevation (m AHD) Gauge Board 0.67 Bore Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec Month 4 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb Baseflow Index

20 GDE Types Pioneer Valley GDE Ecosystem Water Requirements 3. Wetland GDEs Key groundwater attribute FLUX & LEVEL Mapping (limited) Remnants typically riparian

21 Conceptual biophysical model Pioneer Valley GDE Ecosystem Water Requirements

22 EWR Determination Terrestrial / Riparian GDEs Pioneer Valley GDE Ecosystem Water Requirements WBRisk model Soil water availability (PAWC); - initial water source for GDEs - water balance approach (compare dry season transpiration requirement against soil reservoir) Modeling incidence of dry season water shortage (WBRisk); - utilised rainfall record and transpiration data - depending on depth of vadose zone access to groundwater important toward end of dry season, or following a number of below av. rainfall seasons - compare remnant vegetation with depth to water table to assess where groundwater dependence likely to be critical

23 EWR Determination Terrestrial GDEs (cont.) Pioneer Valley GDE Ecosystem Water Requirements VeGAR model (terrestrial GDEs cont.) Vegetation Groundwater Availability Response (VeGAR) model; - vegetation response (transpiration) to changes in groundwater availability (water table decline) - calibrated using field measurements VeGAR simulates ; - hydraulic lift required (root tip to leaf) - xylem water potential and soil matric potential - conductance of the pathway between soil & leaf - rooting depth - root distribution

24 EWR Determination Terrestrial GDEs (cont.) Pioneer Valley GDE Ecosystem Water Requirements 1. Shallow water tables equate to greater proportional dependence of GDEs on groundwater 2. Soil water reservoir will often be an important water source for vegetation, in addition to groundwater 3. Risk should be a consideration in calculating GDE EWRs 4. In terms of describing EWRs for terrestrial and riparian GDEs, there appear to be three stages of GDE response

25 EWR Determination Terrestrial GDEs (cont.) Pioneer Valley GDE Ecosystem Water Requirements Stage 1; - water tables <4 m deep - high probability of dry season water shortage Stage 2; - water tables 4 to 10 m deep - moderate to medium risk of dry season water shortage Stage 3; - water tables >10 m deep - low risk of dry season water shortage Rooting Depth (m) Risk (per year) 1 KEY: Water table depth range 0 to 4 m Water table depth range 4 to 7 m Water table depth range 7 to 10 m Water table depth range >10 m Stage 1 response Stage 2 response Stage 3 response

26 EWR Determination Baseflow GDEs Pioneer Valley GDE Ecosystem Water Requirements Rainfall 360 Baseflow is of major importance 1.00 for ecosystems in Baseflow Index unregulated / unsupplemented streams (eg. Sandy Creek & perhaps Alligator Creek) Rainfall (mm/month) 240 Phase 1 work identified baseflow contribution to Sandy Creek flow from the North & South branches to Palm Creek confluence 0 Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec BI of 0.5 or greater typically occurs over 6 months of Month each year Groundwater Pumping (ML/month) Baseflow Index Groundw ater Abstractions Baseflow Index Baseflow Index 0 Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec Month 0.00

27 EWR Determination Baseflow GDEs (cont.) Pioneer Valley GDE Ecosystem Water Requirements EWR corresponds low flow risk level %age of pre-development mean annual flow WRP mean annual flow = 63 ML/day environmental flow = ~50 ML/day low flow = >1 ML/day Phase 1 flows below 90 ML/day almost entirely derived from baseflow

28 EWR Determination Baseflow GDEs (cont.) Pioneer Valley GDE Ecosystem Water Requirements Baseflow (ML/day) Critically important flow band 0.10 Probability of Exceedance environmental flow exceeded around 20% of time low flow exceeded around 80% of time 1.00

29 EWR Determination Baseflow GDEs (cont.) Pioneer Valley GDE Ecosystem Water Requirements Baseflow (ML/day) [2] Nature of Probability of Dependence Less than 1 High (high) flow band for maintenance 0.01 of KEY: Baseflow Exceedance (ML/day) [3] 1 to 50 Proportional 0.20 to 0.80 (moderate to high) More than 50 Proportional 0.20 (moderate) EWR Stage 1 Response: C onsidered critically im portant hyporheic and in-stream GDEs. Not to be reduced as a result of groundwater development. Stage 2 Response: C onsidered critically im portant flow band for maintenance of hyporheic and in-stream GDEs. May be reduced for short 0.10 intraannual periods only Water quality not considered to be an at-risk attribute. The attribute of level is inherent Baseflow in below achieving 1 ML/day the desired attribute Stage of flux 1 response / flow. 3. Probability that baseflow will exceed nominated flow band (rounded to nearest Baseflow range 1 to 50 ML/day Stage 2 response 0.05) Baseflow greater than 50 ML/day Stage 3 response Probability of Exceedance Stage 3 Response: Possibly not critically im portant for GDEs, but m ay be important for aquatic ecosystems. Notes: 1. In relation to stream gauging data at Station A126001A (near Homebush).

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