A new approach to determining environmental flow requirements: Sustaining the natural values of...

A new approach to determining environmental flowrequirements: Sustaining the natural values offloodplains of the southern Murray-Darling BasinBy Paul Peake, James Fitzsimons, Doug Frood, Mel Mitchell, Naomi Withers, Matt White andRick Webster

Paul Peake is Remnant Vegetation Investigation

Team Leader at the Victorian Environmental Assess-

ment Council (VEAC) (8 Nicholson Street, East Mel-

bourne VIC 3002, Australia; Tel: +61 3-9637-9896;

Email: [email protected]). James Fitzsi-mons was a Senior Project Officer at VEAC and is

currently with The Nature Conservancy (Suite 3-04,

60 Leicester Street, Carlton VIC 3053, Australia) and

the School of Life and Environmental Sciences, Dea-

kin University (221 Burwood Highway, Burwood

VIC 3125, Australia; Email: james.fitzsimons@

deakin.edu.au). Doug Frood is a botanist with

Pathways Bushland and Environment (PO Box 360,

Greensborough VIC 3088, Australia; Email:

[email protected]). Mel Mitchell is a Senior

Project Officer at VEAC (8 Nicholson Street, East Mel-

bourne VIC 3002, Australia; Email: mel.mitchell@

dse.vic.gov.au). Naomi Withers was Senior GIS

Project Officer with VEAC and is now with the

Department of Sustainability and Environment (8

Nicholson Street, East Melbourne VIC 3002, Australia;

Email: [email protected]). Matt White is

an ecologist with the Arthur Rylah Institute for Envi-

ronmental Research, Department of Sustainability

and Environment (123 Brown Street, Heidelberg VIC

3084, Australia; Email: [email protected]).

Rick Webster is a Director ⁄ Ecologist at Ecosurveys

Pty Ltd (PO Box 13, Deniliquin NSW 2710, Australia;

Email: [email protected]). This paper is a

result of work commissioned by the Victorian Envi-

ronmental Assessment Council to better identify the

environmental watering needs of flood-dependent

species and ecosystems in the southern Murray-

Darling Basin.

Summary Large overbank flood events play an important role in maintaining large-scale ecological processes and connectivity along and across the floodplains and betweenthe rivers and their floodplains in the southern Murray-Darling Basin. However, the regulationof rivers means that extensive overbank flooding can only occur in the rare circumstance ofextreme flood events. Recent environmental water allocations have focussed on the largestfloodplain blocks (‘icon’ sites) and a small set of specific values (e.g. colonial nesting water-birds), as well as on trialling fine-scale manipulation of infrastructure (e.g. pumping) to waterrelatively small areas. There has been no comprehensive systematic assessment of the entirefloodplain and its wider set of flood-dependent natural assets (such as ecosystems and spe-cies; herein referred to as ‘natural values’) to maximise the effectiveness of environmentalwater use and to catalogue values likely to be lost. This paper describes an assessment ofsome 220 000 ha found to support flood-dependent natural values in Victoria. We mappedthe geographic distribution and estimated components of the flooding requirements (naturalflooding frequency, and maximum period without flooding and minimum duration of eachflooding event before significant deterioration) for each natural value. Using an example ofone stretch of the River Murray, we show how the resultant spatial data can be used withfloodplain inundation modelling to compare the outcomes of real or planned environmentalwatering events; potentially providing tools for management agencies to conserve a widerrange of floodplain values than is currently the case. That is, water managers and the publiccan see what ecosystems and threatened species are intended to be maintained by environ-mental watering and what values are intended to be abandoned across the whole floodplain,rather than just seeing the small subset of values and ‘icon’ sites that are intended to bemaintained. Examples are provided to illustrate how information about the location, waterrequirements and extent covered by potential floods for specific values can be used to buildadaptive watering strategies for areas as large as the whole floodplain.

Key words: critical flood intervals, environmental flows, flood requirements, floodplains, threa-tened species.

Introduction

The deteriorating state of the Murray-

Darling Basin has been a cause of con-

siderable concern amongst ecologists, land

managers, politicians and the communities

living in and relying on the basin. The

guide to the Murray-Darling Basin Plan

(e.g. MDBA 2010) and two significant

investigations into future land and water

management in Victoria and New South

Wales (VEAC 2008a; NRC 2009) are recent

attempts to redress this deterioration.

Pulsed flooding is the major factor influ-

encing biota in river-floodplain systems

(Ballinger & Mac Nally 2006). The flood-

plains of northern Victoria support a

unique biota in an otherwise semi-arid

environment because of overbank riverine

flood events resulting from large rain

events in the somewhat distant Great

Dividing Range to the south and east.

These flood events also maintain ecological

connectivity along the length of the flood-

plains, across the floodplains and between

the major rivers and their floodplains,

thereby playing a crucial role in the land-

scape ecology of the region (Ballinger &

Mac Nally 2006). The floodplain forests

and woodlands not only provide important

habitat for a range of forest- and woodland-

adapted plants and animals, but also act as

a pathway extending the geographic range

M A N A G E M E N TR E P O R T

128 ECOLOGICAL MANAGEMENT & RESTORATION VOL 12 NO 2 AUGUST 2011 ª 2011 Ecological Society of Australia

doi: 10.1111/j.1442-8903.2011.00581.x

EcologicalSociety of Australia

of a number of species, particularly birds

(e.g. Tzaros 2001).

The rivers of northern Victoria, how-

ever, are now highly regulated, and much

of their flows are diverted for irrigated agri-

culture. They are currently managed so

that extensive overbank flooding occurs

only when water storages are full and spill-

ing at sufficient volumes for the rivers to

break their banks (VEAC 2006). As a result

of this management regime, the frequency

of small and moderate floods has declined

to around a third or less of the natural

frequency of flooding for most of the

floodplain (e.g. DSE 2008a). Consequently,

there are now many indications of wide-

spread substantial decline in the biodiver-

sity of the floodplains including an

increase in the number of dead and dying

River Red Gum (Eucalyptus camaldulen-

sis) and Black Box (E. largiflorens) trees

(MDBC 2003; Cunningham et al. 2007),

reduced River Red Gum growth rates

(VEAC 2008a), and the development of

acid sulfate soils (McCarthy et al. 2006).

Despite a recent flood event, climate

change predictions translate to further

reductions in overbank flood frequency

(DSE 2008a) – and hence loss of biodiver-

sity into the future – if current river man-

agement continues. Reduced precipitation

and increased evapo-transpiration resulting

in reduced runoff are likely to greatly

reduce frequency and extent of floodplain

inundation (e.g. DSE 2008a).

As a result, artificially generated and

manipulated environmental watering has

been increasingly relied upon to sustain

floodplain forests and wetlands along the

Murray Valley in recent years. However,

this watering has been limited to specific

places and values, such as parts of large for-

est ⁄ woodland blocks (i.e. ‘icon’ sites) and

colonial nesting waterbirds (e.g. Cooling

et al. 2002; Leslie & Ward 2002; Stewart &

Harper 2002), and the basis for the selec-

tion of watered sites and specific values

ahead of others is often unclear. Environ-

mental watering requires strategic plan-

ning to ensure the most effective use of

water in sustaining biodiversity assets. A

prerequisite for such planning is a compre-

hensive, systematic, spatially explicit and

publicly transparent inventory of flood-

dependent natural values as a basis for

allocating scarce and expensive water and

for determining priorities for infrastructure

investment to natural assets. However,

consideration of the water requirements of

the full suite of floodplain ecosystems and

taxa has been limited (Ballinger & Mac

Nally 2005).

This situation is not unique to the Mur-

ray-Darling Basin or Australia. Internation-

ally, fish are typically used as an indicator

species for flood requirements (e.g. Richter

et al. 2006; Wang et al. 2009; Beilfuss &

Brown 2010) as they can be relatively

easily monitored. Indeed, Smakhtin (2008)

notes very few countries have set clear

procedures for environmental flow estima-

tion and allocation.

In this paper, we interpret for managers

an approach to environmental watering

that explicitly focuses on the flooding

requirements of species and ecosystems

across the landscape. This approach high-

lights, for the first time, those species and

ecosystems most in need of flooding and

the locations where they occur. The

approach is management focused and can

easily incorporate new ecological and bio-

physical data. The process aims to move

beyond the ‘icon sites’ approach to view

the River Murray floodplains as a dynamic

interconnected system. This is based on an

analysis undertaken as part of the Victorian

Environmental Assessment Council’s final

recommendations for the floodplain forests

and woodlands of northern Victoria (VEAC

2008a,b). During this analysis, we com-

piled data on and mapped the flood

requirements for all flood-dependent vege-

tation types, as a surrogate for ecosystems,

and most flood-dependent threatened spe-

cies along the River Murray and its major

tributaries in Victoria. (The full dataset is

published in a separate paper, Fitzsimons

et al. 2011.)

Using a case study in the Robinvale area

of the River Murray, this paper provides an

example of how the dataset can be used to

quantify the proportion of species habitats

receiving water under different flooding

regimes. The approach provides the basis

for a transparent, flexible and useable eco-

logical dataset to inform decision-making,

auditing and monitoring of environmental

management outcomes in the northern

Victorian floodplains, and beyond.

While vegetation types and threatened

species are typically the foremost natural

values targeted in analyses such as this, we

make a range of suggestions for future

work that would further improve the envi-

ronmental management of the floodplains,

including the incorporation of additional

natural values such as high species rich-

ness, key non-threatened species and eco-

logical connectivity.

How the Analysis of FloodingNeeds was Undertaken

Assessment area

The assessment covered the Victorian

floodplains of the Murray, Goulburn,

Ovens and King Rivers downstream of

Lake Hume, Goulburn Weir, Porepunkah

and Cheshunt respectively – an area of

approximately 507 000 ha, collectively

referred to here as the River Murray flood-

plain. The area is a subset of the Victorian

Environmental Assessment Council’s River

Red Gum Forests Investigation area (see

Fitzsimons 2006; VEAC 2006) (Fig. 1).

Determining the flooding

requirements of natural

values

Full details of how the flooding require-

ments for vegetation types and threatened

flora and fauna were derived are provided

in Fitzsimons et al. (2011, contact the

corresponding author for a copy) and are

summarised as follows.

Publicly accessible geospatial data main-

tained by the Victorian Department of

Sustainability and Environment (DSE) (i.e.

relating to vegetation types and threatened

fauna and flora) were used as the basis of

this analysis. Ecological vegetation classes

(EVCs) are the principal units for native

vegetation classification and mapping for

land-use planning and management in Vic-

toria (Parkes et al. 2003). These are units

in a vegetation classification system that

are differentiated through a combination of

floristic, life form and ecological character-

istics, and through an inferred fidelity to

particular environmental attributes.

The major determinant of vegetation

type in this region is riverine flooding; as

opposed to flooding or watering solely

M A N A G E M E N T R E P O R T

ª 2011 Ecological Society of Australia ECOLOGICAL MANAGEMENT & RESTORATION VOL 12 NO 2 AUGUST 2011 129

from local rainfall. Within flood-prone

areas, the major determinants of occur-

rence for most EVCs are variations in flood

regime, particularly flood frequency and

duration. In the assessment, we built on

this spatial dataset by identifying the flood-

ing requirements for each flood-dependent

EVC, based on the life-history traits, toler-

ances and competitive advantages of its

dominant and characteristic plant taxa.

This new information was appended to

existing EVC polygons. As few of the plant

species have been the subject of detailed

autecological studies, estimates of flooding

regime variables were based on a combina-

tion of searches of the available literature

supplemented by the expert opinion of DF

and MW who were closely involved in the

circumscription and mapping of EVCs in

2006.

To identify flood requirements for EVCs

in the region, we first identified flood-

dependent EVCs, i.e. those that were

(a) likely to significantly decline in condi-

tion across the region in the absence of

overbank flows from adjoining rivers or

(b) depended on geomorphological pro-

cesses such as the deposition of silts, and

the regulation of ground water depth and

chemistry. In the absence of long-term

historical information for the EVCs, the nat-

ural flood frequency for each flood-depen-

dent EVC was estimated based on what is

known or surmised by our expert assessors

of the flooding requirements and toler-

ances of characteristic species and the

physical (including hydrological) condi-

tions at sites of occurrence, particularly in

comparison with these parameters for

adjoining or similar EVCs. The critical inter-

val (the estimated maximum period that an

EVC can persist without flooding and

remain capable of returning to its refer-

ence or benchmark condition) was esti-

mated on the basis of familiarity of the

assessors with field indications of decline,

combined with a knowledge of past flood

intervals. We did not use hydrological mod-

elling to determine a volume for this pro-

cess as there was no hydrological model

for the entire floodplain at the time and

providing a volume was not the intent of

the approach. However, in this paper, we

do provide an example of how hydrologic

modelling could be used based on pre-

existing CSIRO models (see below).

Finally, the minimum flood duration

required to maintain each EVC in a

condition comparable to its reference state

(DSE 2008b) was estimated based on the

requirements of characteristic species and

physical conditions at sites of occurrence.

For flora, point records for listed threa-

tened or rare species that occurred in the

study area were extracted from the DSE’s

Flora Information System (FIS) (as at May

2007). Each taxon on this list was then

classed as flood-dependent or not by apply-

ing the same definition of ‘flood-depen-

dent’ that was used for the identification of

flood-dependent EVCs to what was known

of the taxon’s ecology and occurrence,

including a review of relevant literature

and FIS data. As little specific information

on the flood requirements exists for most

species, the flood requirements of the prin-

cipal EVCs in which these species

occurred was adopted as the flooding

requirements for that taxon. The distribu-

tion of each species was then mapped as

the spatial extent of the coincident EVCs.

Records for threatened fauna (birds,

mammals, reptiles and amphibians) were

extracted from DSE’s Victorian Fauna Data-

base and Birds Australia’s Atlas data (in

May 2008), and flooding requirements

were determined through discussions with

experts (see ‘Acknowledgements’ below),

and through reviewing relevant literature

(see Fitzsimons et al. 2011 for a list of pub-

lished sources used). The habitats of most

fauna taxa were specified as one or more

EVCs, which were then mapped as the

sites for each taxon within its known local

geographic distribution. The natural flood

frequency, critical interval and minimum

flood duration estimates for the EVC(s)

were then assigned to the sites. However,

for some taxa, notably colonially nesting

waterbirds, more specific information

derived from site visits was available and

used to map site locations and specify

watering requirements.

Geospatial data processing

A single digital geospatial layer was created

incorporating all flood-dependent EVC

polygons from the DSE’s Corporate Geo-

spatial Data Library. For threatened flora

and fauna, a separate digital geospatial

layer was created for each taxon using

new polygons where necessary but mostly

using pre-existing polygons – usually EVC

0 40km

Present study area

VEAC (2006) investigation area boundary

Area shown in Figures 2, 3

N

New south wales

Melbourne

River Murray

VictoriaSouth

Australia KiewaRiver

GoulburnRiver King

River

OvensRiver

16080

Figure 1. Location of VEAC River Red Gum Forests Investigation area and floodplain values

mapped in this analysis.



polygons but sometimes others according

to details specific to particular taxa or sites

as described above. New polygons were

digitised from hand-drawn polygons on

topographic maps or aerial photos. Natural

flood frequency, critical interval and mini-

mum duration estimates were assigned to

all polygons within a geographic informa-

tion system (ArcGIS).

Identifying flood-dependent

values

A major aim of the analysis was to identify

a broad range of natural values – such as

vegetation units, threatened flora and

fauna – that managers could take into

account when identifying conservation

management goals. To provide a visual rep-

resentation of the relative number of differ-

ent flood-dependent values at any one site,

geospatial layers for EVCs and for each of

the threatened species were overlayed, a

composite layer generated and a new field

for the number of distinct features

attached to each resultant polygon. Over-

laying the composite natural values layers

with the CSIRO River Murray Floodplain

Inundation Model (RiM-FIM) (Overton

2005) was undertaken in the Robinvale

area of northwestern Victoria to show

which values would or would not receive

water under differing flooding scenarios.

Outputs Relevant toManagers

Data for EVCs and

threatened taxa

Some 224 247 ha of extant vegetation on

the River Murray floodplains in Victoria

were determined to be at least partially

flood-dependent including 162 266 ha on

public land. This vegetation comprised

110 EVCs, confirming that a large area of

significant ecological diversity is at risk

from inadequate flooding (see Fitzsimons

et al. 2011 for the full description of the

primary findings).

Examples of natural flood frequency,

critical interval, minimum duration and

location information collected for a subset

of the flood-dependent EVCs are provided

in Table 1a. Natural flooding frequencies

ranged from as many as 3–4 flood events

every 4 years for Aquatic Herbland and a

further 20 EVCs, through to one flood

event in 20–40 years for Riverine Cheno-

pod Woodland. Critical intervals to main-

tain healthy ecosystems ranged from one

flood event every 2 years for around 30

EVCs to one flood every 30–50 years for

some EVCs dominated by Black Box. A

visual representation of the critical inter-

vals for EVCs is presented in Map D of

VEAC (2008a). Minimum durations of

inundation ranged from <1 month to

6–36 months (Table 1).

In terms of threatened species, 124 rare

or threatened plant taxa were classified as

at least partly flood-dependent of which 68

were sufficiently well known for their dis-

tributions to be mapped reliably (see Fitzsi-

mons et al. 2011 for the full list and

Table 1b as an example). Of the 62 threa-

tened vertebrate fauna taxa (excluding

fish) found to be flood-dependent, 51 were

sufficiently well known for their distribu-

tions to be mapped reliably (see Table 1c

as an example). A visual representation of

the critical intervals for threatened species

is presented in Map E of VEAC (2008a).

Mapped outputs – and an

example of how they can be

applied in management

planning

Figure 2 and Table 2 provide examples of

how the digital mapping generated in this

project can be used to compare the extent

to which different modelled inundation

events assist or fail to assist in sustaining

floodplain natural values for a particular

area. Figure 2 shows the predicted extent

of flooding for three different-sized floods

along a sample reach of the River Murray

floodplain east of Robinvale, resulting from

three different flow rates along the river

channel: 20, 81 and 159 GL per day, which

correspond to very small, moderate and

large overbank floods, respectively. To give

some context, prior to 1981 for example,

sustained flows (more than five consecu-

tive days) of 20 GL per day occurred on

average in 8 of every 10 years. Sustained

flows of 81 and 159 GL per day occurred

twice and once (respectively) in every 10

years, on average. In the decade to the end

of 2009, however, there were only 5 years

in which sustained flows of 20 GL per day

occurred and none in which sustained

flows of 81 or 159 GL per day occurred

(MDBA, unpublished data, 2011). While

Figure 2 is a composite of all flood-depen-

dent EVCs and threatened species, maps

can be readily produced for individual

EVCs, species or combinations thereof.

The area of each flood-dependent EVC,

threatened species habitat and the percent-

age of these areas inundated by the three

different flood levels are outlined in

Table 2. For example, <5% of almost all val-

ues are inundated by a very small flood

whereas over three-quarters of Floodplain

Grassy Wetland EVC, half the Regent Par-

rot (Polytelis anthopeplus monarchoides)

breeding habitat and 100% of Silver Salt-

bush (Atriplex rhagodioides) habitat is

inundated in a large flood.

Identifying deficiencies in

current management

The large multifactorial dataset generated

by our original study and analysis can be

readily used to provide insight into many

interesting questions. Perhaps the most

compelling of these would address the

comprehensiveness of the current ‘icon

sites’ approach as illustrated by the follow-

ing simple example.

The eastern subspecies of the Regent

Parrot occurs in the Murray Mallee of New

South Wales, Victoria and South Australia

and is listed as threatened nationally and in

each of these states. It feeds in mallee vege-

tation but breeds in hollows in old flood-

plain eucalypts – typically in loose colonies

in copses of tall, straight, leafy trees. In the

absence of adequate flooding, these trees

would deteriorate in condition, die or not

be recruited in the long term, all of which

would adversely affect the Regent Parrot

population. Because there have been sys-

tematic searches for breeding sites, it is

one of the few species for which specific

sites – the location of all known breeding

sites in the study area – could be mapped,

as opposed to using EVC maps to generate

habitat maps as documented above (Web-

ster 2004).

This process resulted in 26 breeding

sites being mapped, with an estimated

minimum flood frequency of every 5–

7 years. Significantly, ten of these sites are

outside of The Living Murray’s ‘icon’ sites,



Table 1. Examples of natural flood frequency, critical interval, minimum duration and location information collected for some (a) flood-dependent

Ecological Vegetation Classes, (b) significant plant species and (c) significant fauna species (For full details of all mapped natural values, see Fitzsimons

et al. 2011)

(a)

Ecological vegetation class Natural flood frequency (years) Critical interval (years) Minimum duration (months)

Alluvial Plains Semi-arid Grassland 1 in 2–15 25 1.5–6Aquatic Herbland 3–4 in 4 2 6–12Billabong Wetland Aggregate Variable 2 (variable) >6Floodplain Riparian Woodland 3–5 in 10 7 <1Grassy Riverine Forest 2–4 in 4 4 1–4Red Gum Swamp 2–3 in 3 3 4–9Riverine Chenopod Woodland 1 in 10–25 (1 in 20–40 Atriplex community) 30–50 <1–3

(b)

Name and conservationstatus of plant species*

Wetland ⁄floodplain

dependent†

Importanceof study areapopulation

Relevantflood-dependent EVCs

Mapped Additional information

Native Scurf-pea Cullenaustralasicum (e, L)

Y High Lake Bed Herbland ·

Hoary Scurf-pea Cullencinereum (e, L)

Y High Lake Bed Herbland 4 Drying phase of shallow lakes

Small Scurf-pea Cullenparvum (e, L)

Y(in north)

High Sedgy Riverine Forest (upper edge),Riverine Swampy Woodland

4

·Upper edge of flooded zone,flood-dispersed seed pods

Annual Flat-sedge Cyperusnervulosus (e, L)

Y High Drainage-line Aggregate, RiverineSwamp Forest, Riparian

Slender Love-grass Eragrostisexigua (e)

Y High Drainage-line Aggregate 4

Jerry-jerry Ammanniamultiflora (v)

Y High Drainage-line Aggregate, LignumShrubland, Lake Bed Herbland,Alluvial Plains Semi-arid Grassland

4 Annual of creeklines,lacustrine – followingrecession

(c)

Name andconservation statusof animal species

Location and flooding requirements

Little Egret Egrettagarzetta (endangered)

Sites mapped: Breeding sites: All DSE wetland polygons and other points with breeding records and a surrounding2 km buffer (for both)Non-breeding sites:1. Lakes Ranfurley and Hawthorn: all areas of Lake Bed Herbland2. Lakes Hattah, Little Hattah, Lockie, Yerang, Mournpall, Bulla and Arawak: all areas of Lake Bed Herbland3. Ovens River c. 1.5 km E of Hume Highway (Wangaratta Bypass): all areas of Floodplain Riparian Woodland andFloodplain Wetland Aggregate within 1 km of record site4. Ovens River c. 4 km E of Hume Highway (Wangaratta Bypass): all areas of Floodplain Riparian Woodland, FloodplainWetland Aggregate and Water Body – natural or manmade within 1 km of record site5. Ovens River SE of Whorouly: all areas of Swampy Woodland, Drainage-Line Aggregate, Floodplain WetlandAggregate and Water Body – natural or manmade within 1 km of record siteMinimum flood frequency: Breeding sites: 1 in 5 years; Non-breeding sites: as per EVCs; 1 in 2 years for WaterBodyFlood duration: Breeding sites: 5 months; Non-breeding sites: as per EVCs, 6–12 months for Water BodyHabitat ⁄ Location: All post-1960 breeding records in VFD and literature selected and mapped. Non-breedingrecords are sites with two or more post-1970 recordsRelative importance of study area: High – the study area nesting sites are the largest in Victoria (there are fewin Victoria outside the study area) albeit not recent (2010 breeding in Barmah forest is not included in this analysis)and the species is endangered

De Vis’ Banded SnakeDenisonia devisi(vulnerable)

Sites mapped: Lake Bed Herbland, Floodway Pond Herbland, Shallow Freshwater Marsh, Intermittent SwampyWoodland at site recordsMinimum flood frequency: as per EVCs. Flood duration: as per EVCsHabitat ⁄ Location: Site records from DSE (see also Clemann et al. 2007) and advice on EVCs from expert opinion.Watercourse ⁄ wetland-reliant as frogs are the main dietRelative importance of study area: Recently discovered in Victoria and entire known range in Victoria is in studyarea – so important. Nearest known site locality is some 500 km away at Broken Hill in NSW. Vulnerable on the DSE2007 Advisory List and range restricted

*Conservation status: e (endangered), v (vulnerable), L (listed under the Flora and Fauna Guarantee Act 1988). †Y – Taxa apparently requiring ⁄responding to inundation. EVC: Ecological vegetation classes.



for which regular environmental watering

is planned. Other Regent Parrot breeding

areas interstate and along the Wimmera

River in Victoria are at least as unlikely to

receive adequate flooding as those covered

in our analysis. Further analysis of our

mapped dataset is likely to reveal similar

deficiencies for many other taxa and eco-

systems.

Discussion

The primary purpose of this analysis is to

facilitate the development of floodplain

watering strategies that maximise the effec-

tiveness of whatever watering is under-

taken in sustaining natural values. This is

enabled by providing digital mapping that

can be used to transparently predict the

extent to which any given inundation

event assists in sustaining the natural val-

ues of the floodplain. By compiling the

results of these analyses for many such

events, it is possible to develop floodplain

watering strategies covering the entire

River Murray floodplain for periods compa-

rable to the largest estimated flood fre-

quencies (i.e. 20–40 years). The predicted

outcomes of the different strategies for

floodplain natural values could then be

compared and the most favourable practi-

cable strategy adopted for implementation.

The essence of this comprehensive

mapping approach enables the develop-

ment of adaptive watering strategies that

are readily communicated to the general

public and facilitate transparent modifica-

tion in response to new information or

changes to key factors such as water avail-

ability. Importantly, it furthers the debate

about how much water should be allo-

cated to the environment by documenting

the ‘winners’ and ‘losers’ (of species and

ecosystems) in any watering event or ser-

ies of watering events.

Such strategies would be developed by

bringing together the most effective water

regimes for each of the natural values tar-

geted for protection along the entire length

of the floodplain. Many of these regimes

would be developed through their own

adaptive process. For example, if a manage-

ment agency was interested in maintaining

River Red Gums in the Robinvale area

(Fig. 2), they might interrogate our data set

for Grassy Riverine Forest – the predomi-

nant EVC supporting this species. This EVC

requires watering every 4 years to maintain

condition (its critical interval – Table 1)

and is predicted to be barely inundated in a

20 GL ⁄ day flood (2% of extent), 27 and

35% inundated in 81 and 159 GL ⁄ day

floods, respectively (Table 2). Based on this

information, the manager, with consider-

ation of other factors such as the approxi-

mate amount of environmental water

available, might judge that flows of at least

81 GL ⁄ day be generated once every 4 years

unless such flows occur naturally. This

Very small flood(20 gigalitres per day)

Not flooded

Extent of flooding(with flows of 20, 81 or 159 GL/day)Frequency of

flooding required(years)

1 in 2–5

1 in 7

1 in 15–30

Lake Powell

Lake Carpul

Moderate flood (81 gigalitres per day)

Large flood(159 gigalitres per day)

0 2.5km

2015105

Flooded

Figure 2. Examples of coverage of flood-dependent natural values for various flood scenarios in

the Robinvale area. Note: The flooding extents shown in red are based on outputs from the CSIRO

River Murray Floodplain Inundation Model (RiM-FIM) which is derived from satellite imagery of

actual floods. This figure provides an example of how the digital natural values mapping generated

in the present study can be applied. It is not intended that this figure represent actual outcomes of

applying these amounts of environmental water. The maps apply to the Victorian side of the River

Murray only.



Table 2. Area and percentage of natural values in the Robinvale region inundated by the three flood extents shown in Figure 2

Area of EVCor habitat (ha)

Percent of mapped EVC or habitatcovered by various flood extents

Very small Moderate Large

Ecological Vegetation ClassFloodplain Grassy Wetland 63 3 71 77Floodway Pond Herbland 370 1 37 47Grassy Riverine Forest 678 2 27 35Grassy Riverine Forest ⁄ Floodway Pond Herbland Complex 567 2 22 28Intermittent Swampy Woodland 1433 1 27 38Lake Bed Herbland 130 0 0 0Lignum Shrubland 3550 0 5 12Lignum Swamp 562 0 2 7Lignum Swampy Woodland 5488 0 5 11Riverine Chenopod Woodland 5035 0 5 8Riverine Grassy Woodland 980 0 4 9Shallow Freshwater Marsh 394 0 42 51Shrubby Riverine Woodland 1972 1 24 37Spike-sedge Wetland 17 0 62 71Sub-saline Depression Shrubland 82 0 0 0Tall Marsh 42 0 9 21

Threatened FaunaApostlebird Struthidea cinerea 6746 0 3 7Blue-billed Duck Oxyura australis 434 0 0 0Brown Quail Coturnix ypsilophora 35 0 0 0Inland Carpet Python Morelia spilota metcalfei 16 452 0 12 19Diamond Dove Geopelia cuneata 168 0 0 0Diamond Firetail Stagonopleura guttata 121 0 2 6Freckled Duck Stictonetta naevosa 2700 0 2 3Grey-crowned Babbler Pomatostomus temporalis 215 0 0 0Hardhead Aythya australis 592 0 0 0Musk Duck Biziura lobata 592 0 0 0Nankeen Night-Heron Nycticorax caledonicus 1690 0 4 6White-bellied Sea-Eagle Haliaeetus leucogaster 550 0 0 0Regent Parrot Polytelis anthopeplus monarchoides 321 1 29 49

Rare or Threatened FloraAnnual Spinach Tetragonia moorei 89 0 2 3Bluish Raspwort Haloragis glauca f. glauca 249 0 13 20Common Joyweed Alternanthera nodiflora 259 0 0 0Cotton Sneezeweed Centipeda cunninghamii 88 0 42 65Desert Lantern Abutilon otocarpum 84 0 0 3Desert Spinach Tetragonia eremaea s.s. 43 0 4 11Dwarf Bitter-cress Rorippa eustylis 77 0 0 0Goat Head Malacocera tricornis 559 0 2 4Hoary Scurf-pea Cullen cinereum 81 0 10 15Mealy Saltbush Atriplex pseudocampanulata 42 0 0 0Native Couch Cynodon dactylon var. pulchellus 729 1 22 35Native Peppercress Lepidium pseudohyssopifolium 518 1 9 13Pale Plover-daisy Leiocarpa leptolepis 41 2 5 7Pale Spike-sedge Eleocharis pallens 26 0 0 0Purple Love-grass Eragrostis lacunaria 182 0 0 0Reader’s Daisy Brachysome readeri 380 0 2 7Riverina Bitter-cress Cardamine moirensis 132 1 25 39Riverine Flax-lily Dianella porracea 69 0 0 0Silver Saltbush Atriplex rhagodioides 23 8 79 100Smooth Minuria Minuria integerrima 38 0 0 0Spear-fruit Copperburr Sclerolaena patenticuspis 432 0 6 13Spiny Lignum Muehlenbeckia horrida horrida 71 0 0 0Spotted Emu-bush Eremophila maculata var. maculata 236 0 2 3Spreading Emu-bush Eremophila divaricata divaricata 776 2 14 18Squat Picris Picris squarrosa 509 2 33 55Summer Fringe-sedge Fimbristylis squarrosa 381 0 1 5Sweet Fenugreek Trigonella suavissima 86 0 0 0



regime would then be integrated with

numerous regimes for other values to come

up with an overall strategy, which could

then be implemented and refined through

analysis of actual flooding extents and

refinement of critical intervals for particular

values.

In some cases, the local regimes may

end up being separate from any broader

regime. For example, Lakes Powell and

Carpul near Robinvale in northwest

Victoria have high concentrations of natu-

ral values (Fig. 3) with critical intervals of

2–5 years, but are not predicted to be

inundated even in large floods (Fig. 2).

That is, assuming this predicted lack of

flooding in these areas was confirmed by

site-specific investigation (such as actual

flooding extent in past and future

overbank flows of various sizes), these

areas would be prime candidates for works

such as levees, regulators or pumping to

meet their flooding requirements – particu-

larly given that they are terminal lakes that

would not require large volumes of water

flowing down the river channel in order to

meet flooding duration requirements. The

natural values of these lakes would then be

sustained through a small local pumping

regime specific to the lakes and not as part

of broader regimes targeting many values

in this part of the floodplain.

The allocation of water resources in the

Murray-Darling Basin to the environment on

the one hand, and consumptive uses on the

other is one of Australia’s most important

environmental challenges. If significant

social and regional economic costs are a

potential result of sufficient water being

made available for the environment, then it

is important that the case for such use clearly

articulates its environmental benefits.

Our results greatly substantiate the case

for securing and using of water for the

environment, and in particular for flood-

plain watering, by showing that:

1 There are substantial numbers of eco-

systems and threatened species that are

dependent on environmental watering.

2 It is possible to compile, map and quan-

tify flooding requirements for a sub-

stantial proportion of flood-dependent

species and ecosystems.

3 It is possible (as a result of this map-

ping) to investigate the benefits of and

optimality of environmental watering,

to values at risk as a result of insuffi-

cient watering.

By way of example, the data presented

from a part of the study area near Robin-

vale Victoria demonstrate the application

of our results. In combination with even

relatively cursory information about flood-

plain watering and key values, it is possible

to identify values likely to be at greatest

risk. For the nationally vulnerable eastern

subspecies of the Regent Parrot, for exam-

ple, a large majority of breeding sites are

along the River Murray and highly depen-

dent on riverine flooding. Relatively few of

these sites are within The Living Murray

icon sites that are currently considered the

highest priority areas for environmental

watering. In the context of river regula-

tion, these breeding sites are unlikely to be

flooded regularly without intervention –

our results suggest only 49% of sites would

be inundated by a large flood, which is

Legend

EVCs and threatened speciesNumber of values present

17 – 24

9 – 10

13 – 1415 – 16

11 – 12

1

2

7

8

5 – 6

3 – 4

Lake Powell

Lake Carpul

0 2.5km

2015105

Figure 3. Compilation of flood-dependent natural values on the Victorian side of the River Mur-

ray in the Robinvale area.

Table 2. (Continued)

Area of EVCor habitat (ha)

Percent of mapped EVC or habitat covered byvarious flood extents

Very small Moderate Large

Tangled Copperburr Sclerolaena divaricata 127 0 5 14Twinleaf Bedstraw Asperula gemella 1376 1 5 9Warty Peppercress Lepidium papillosum 150 0 6 9Yakka Grass Sporobolus caroli 189 0 1 4Yarran Acacia melvillei 367 1 5 7

Flood extents based on the CSIRO River Murray Floodplain Inundation Model (RiM-FIM) for the following daily flow volumes: Very small (20 GL ⁄ day),Moderate (81 GL ⁄ day), Large (159 GL ⁄ day). EVC: Ecological vegetation classes.



predicted to occur once every several dec-

ades (DSE 2008a). These results clearly flag

the need for further investigation of the

watering of Regent Parrot breeding sites.

There are many other such floodplain val-

ues that our results identify that would

otherwise likely go undetected.

Availabil ity of the database

The geospatial dataset has been transferred

by the Victorian Environmental Assess-

ment Council to the Victorian Department

of Sustainability and Environment follow-

ing the Victorian Environmental Assess-

ment Council’s final recommendations for

the River Red Gum Forests Investigation in

2008. As a result, it is now freely accessible

to land, water and threatened species man-

agers. In addition, the methodology and

conceptual framework used in our analysis

could be easily applied to other jurisdic-

tions with different vegetation mapping

units and different species and in many

cases, different flood requirements.

Future work – development

of strategies

The future of water availability and alloca-

tion for the environment in the Murray-

Darling Basin is the subject of considerable

recent financial investment and major insti-

tutional change (e.g. Connell 2007). The

framework of our analysis and the data it

generated provide essential information to

commence the process of formulating,

selecting and refining floodplain watering

strategies. However, substantial and endur-

ing positive outcomes for biodiversity will

require further work in a number of areas,

outlined below. The highest priority is to

use the results of the analysis and inunda-

tion modelling to initiate the formulation,

comparison and implementation of flood-

plain watering strategies. Development of

such strategies could be undertaken by

environmental water planners and, in our

view, would be enhanced by incorporation

of the following:

1 Refining watering requirement esti-

mates and mapping. Given that the

expert estimates of flooding require-

ments in this paper would underpin

expensive watering programs critical to

the persistence of much of the region’s

biota, it is imperative to address the

uncertainties in these initial estimates.

Environmental water planners could do

this by testing our models against actual

flood events, and a short-term priority

could be given to sensitivity analysis and

the initiation of research and monitoring

to inform ongoing refinement of esti-

mates and strategies in the longer term.

2 Overbank flows and ecological connec-

tivity. The approach to floodplain water-

ing taken here focuses on mapping

discrete natural assets with a view to

meeting their watering requirements. To

also provide the environmental benefits

of extensive overbank floods and the

resultant ecological connectivity (e.g.

Jenkins & Boulton 2003; Ballinger & Mac

Nally 2005), further work would be nee-

ded to quantify and incorporate these

benefits into the formulation and evalua-

tion of floodplain watering – that is, a

quantification of the benefits of large-

scale inundation, additional to those from

themaintenanceof site-specific values.

3 Comparing different values and risks.

In a water-constrained future, further

work is needed to develop a conceptual

framework within which to compare

different sets of values and the risks to

them to optimise potential trade-offs

between values and to provide stake-

holders with transparency and there-

fore confidence in the decision-making

process. Such a framework would also

highlight key data gaps so that they can

be filled.

4 Additional flooding requirement vari-

ables. For at least some EVCs and taxa,

estimates of the following variables

additional to those in this paper are

likely to be important in the develop-

ment of floodplain watering strategies:

depth of inundation, season of inunda-

tion, minimum and maximum flood

frequencies, and duration of periods

without inundation. Minimum flood fre-

quency over a sustained period and

flood seasonality are likely to be a signif-

icant factors for many EVCs and taxa

(Robertson et al. 2001; Bren 2005).

5 Comprehensive taxonomic and eco-

logical coverage. Floodplain watering

strategies should be taxonomically com-

prehensive and, in addition to the taxa

presented in this paper and Fitzsimons

et al. (2011), include fish, invertebrates,

non-vascular plants and regionally sig-

nificant taxa. Similarly, the list of eco-

logical characteristics used to identify

natural values should be comprehensive

and include important characteristics

such as: sites that are likely to assist the

recovery of highly threatened taxa, sites

of high species richness, colony sites

for non-threatened colonial breeding

species, and corridors of habitat which

are important for the movement of

biota. This project and new information

on future flooding regimes (e.g. DSE

2008a) suggest that as insufficient

watering is a major threat to floodplain

biodiversity, a review of the conserva-

tion status of floodplain EVCs and taxa

in Victoria is required.

6 Ongoing incorporation of floodplain

inundation modelling, hydrology, sa-

linisation and local climate. Improve-

ments in inundation models and

information on the effects of groundwa-

ter, soil salinity and variations in local

climate (including those resulting from

climate change) have the potential to

impact significantly on the formulation

and selection of watering strategies and

should be pursued and incorporated

into those strategies as the improve-

ments and new information becomes

available.

Our analysis is the first to consider how

flooding requirements for a broad range of

natural values can be incorporated into

environmental watering strategies. As a

result of the paucity of existing empirical

data and relative urgency associated with

better informing environmental watering

policy and strategies, this analysis was pri-

marily based on expert opinion. However,

the framework readily allows for the incor-

poration of new data, particularly data

gained from empirical field experiments on

flooding requirements of vegetation types

and species. When provided to the agencies

responsible for environmental water alloca-

tion, such data would enable further

improvement in the effectiveness of ongo-

ing environmental watering. Thus, our



approach is both flexible and adaptable,

which is important given the uncertainties

for future flood events based on climate

change predictions (Aldous et al. 2011).

Conclusion

In conclusion, we contend that large areas

of the Victorian, New South Wales and

South Australian floodplain forests are

(despite a recent, rare flood event) highly

vulnerable to severe stress or mortality

owing to lack of sufficient flooding.

Despite significant investments in purchas-

ing water and the delivery of that water in

the Murray-Darling Basin, there is little

understanding of which natural values are

benefiting from this water and which are

not. Our preliminary work shows that an

efficient and effective watering regime to

sustain flood-dependent natural values is

achievable. Identifying all flood-dependent

natural values and estimating their water

requirements should be a high priority

across the entire Murray-Darling Basin. The

approach also has applicability for other

river basins which rely on floodplain inun-

dation to maintain natural values.

Acknowledgements

This project was overseen by Victorian

Environmental Assessment Council mem-

bers. Information and analysis on the fauna

of the study area was provided by Peter

Robertson, Martin O’Brien, Nick Clemann,

Peter Menkhorst, Chris Tzaros, Lindy Lums-

den, Mark Antos, Andrew Silcocks and Shar

Ramamurthy. Jane Roberts, Terry Hillman

and Keith Ward assisted with information

and analysis on the flora and EVCs. Don

Blackmore, Jane Doolan, Ray Evans, Gary

Jones and Julia Reed made valuable contri-

butions to the study more generally. The

CSIRO RiM-FIM data was provided by Shar

Ramamurthy (DSE). Jong Lee, Pradeep

Sharma and Tony McLeod at the Murray-

Darling Basin Authority provided informa-

tion on the frequency of daily river flows

near Robinvale. We thank Tein McDonald,

Barry Hart, Joan Phillips and two anony-

mous referees for helpful comments on

drafts of this paper.

References

Aldous A., Fitzsimons J., Richter B. and Bach L.(2011) Droughts, floods and freshwater eco-systems: evaluating climate change impactsand developing adaptation strategies. Marineand Freshwater Research 62, 223–231.

Ballinger A. and Mac Nally R. (2005) Floodingin Barmah-Millewa Forest: catastrophe oropportunity for non-aquatic fauna. Proceed-ings of the Royal Society of Victoria 117,111–115.

Ballinger A. and Mac Nally R. (2006) The land-scape context of flooding in the Murray-Dar-ling basin. Advances in Ecological Research39, 85–105.

Beilfuss R. and Brown C. (2010) Assessing theenvironmental flow requirements and trade-offs for the Lower Zambezi River and Delta,Mozambique. International Journal of RiverBasin Management 8, 127–138.

Bren L. J. (2005) The changing hydrology of theBarmah-Millewa Forests and its effects onvegetation. Proceedings of the Royal Societyof Victoria 117, 61–76.

Clemann N., Robertson P., Gibbons D. et al.(2007) An addition to the snake fauna of Vic-toria: De Vis’ Banded Snake Denisonia devisi(Serpentes: Elapidae) Waite and Longman.Victorian Naturalist 124, 33–38.

Connell D. (2007) Water Politics in the Murray-Darling Basin. Federation Press, Sydney.

Cooling M. P., Lloyd L. N., Rudd D. J. and HoganR. P. (2002) Environmental water require-ments and management options in GunbowerForest, Victoria. Australian Journal of WaterResources 5, 75–88.

Cunningham S. C., Mac Nally R., White M. et al.(2007) Mapping the current condition of riverred gum (Eucalyptus camaldulensis Dehnh.)stands along the Victorian Murray River flood-plain. A report to the Northern VictorianCatchment Management Authorities and theDepartment of Sustainability and Environ-ment.

DSE (2008a) Sustainable Water Strategy North-ern Region Discussion Paper, Department ofSustainability and Environment, Melbourne.

DSE (2008b) Ecological Vegetation Class (EVC)Benchmarks for Each Bioregion. Departmentof Sustainability and Environment, Melbourne.Available from: http://www.dse.vic.gov.au/dse/nrence.nsf/LinkView/43FE7DF24A1447D9CA256EE6007EA8788062D358172E420C4A256DEA0012F71C (accessed 5 September2008).

Fitzsimons J. A. (2006) Public land use planningusing bioregions and other attributes: deter-mining the study area of the VEAC RiverRed Gum Forests investigation. Proceedingsof the Royal Society of Victoria 118, 75–85.

Fitzsimons J. A., Peake P., Frood D. et al. (2011)Flooding requirements for biodiversity val-ues along the Victorian floodplain of theMurray Valley. Victorian Naturalist 128, 48–85.

Jenkins K. M. and Boulton A. J. (2003) Connectiv-ity in a dryland river: short-term aquaticmicroinvertebrate recruitment following flood-plain inundation. Ecology 84, 2708–2723.

Leslie D. and Ward K. A. (2002) Murray River envi-ronmental flows 2000–2001. Ecological Man-agement and Restoration 3, 221–223.

McCarthy B., Conallin A., D’Santos P. and BaldwinD. (2006) Acidification, salinization and fishkills at an inland wetland in south-eastern Aus-tralia following partial drying. Ecological Man-agement and Restoration 7, 221–223.

MDBA (2010) Guide to the Proposed Basin Plan,Murray-Darling Basin Authority, Canberra.

MDBC (2003) Preliminary Investigations IntoObserved River Red Gum Decline Along theRiver Murray Below Euston. Technical Report03 ⁄ 03. Murray-Darling Basin Commission,Canberra.

NRC (2009) Riverina Bioregion Regional ForestAssessment: River Red Gums and WoodlandForests Recommendations Report. NaturalResources Commission, Sydney.

Overton I. C. (2005) Modelling floodplain inunda-tion on a regulated river: integrating GIS,remote sensing and hydrological models. RiverResearch and Applications 21, 991–1001.

Parkes D., Newell G. and Cheal D. (2003) Assess-ing the quality of native vegetation: the‘habitat hectares’ approach. Ecological Man-agement and Restoration 4, S29–S38.

Richter B. D., Warner A. T., Meyer J. L. and LutzK. (2006) A collaborative and adaptive pro-cess for developing environmental flow recom-mendations. River Research and Applications22, 297–318.

Robertson A. I., Bacon P. and Heagney G. (2001)The responses of floodplain primary produc-tion to flood frequency and timing. Journal ofApplied Ecology 38, 126–136.

Smakhtin V. (2008) Basin closure and environmen-tal flow requirements. International Journal ofWater Resources Development 24, 227–233.

Stewart G. and Harper B. (2002) Barmah-Millewaforest environmental water allocation. WaterScience and Technology 45(11), 217–223.

Tzaros C. L. (2001) Importance of riparian vegeta-tion to terrestrial avifauna along the MurrayRiver, south-eastern Australia. MSc thesis,Deakin University, Melbourne.

VEAC (2006) River Red Gum Forests InvestigationDiscussion Paper. Victorian EnvironmentalAssessment Council, Melbourne.

VEAC (2008a) River Red Gum Forests Investiga-tion Final Report. Victorian EnvironmentalAssessment Council, Melbourne.

VEAC (2008b) Identifying flood-dependent naturalvalues on the Victorian floodplains of the RiverMurray and its tributaries. Version 1.0. Victo-rian Environmental Assessment Council, Mel-bourne. Available from: http://www.veac.vic.gov.au/reports/352-VEAC_Red_Gum_Flood-dependent_natural_values_Report_V1-0.pdf(accessed 13 September 2009).

Wang X., Zhang Y. and James C. (2009)Approaches to providing and managing envi-ronmental flows in China. International Journalof Water Resources Development 25, 283–300.

Webster R. (2004) Surveys of potential RegentParrot Polytelis anthopeplus monarchoidesnesting habitat in Victoria between PiambieState Forest and Lambert Island. Unpublishedreport to Mallee Catchment ManagementAuthority, Mildura.



A new approach to determining environmental flow requirements: Sustaining the natural values of...

Documents

Transcript of A new approach to determining environmental flow requirements: Sustaining the natural values of...