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A methodology for historical assessment of compliancewith environmental water allocations: lessons from theCrocodile (East) River, South AfricaEdward Riddella, Sharon Pollardb, Stephen Malloryc & Tendai Sawunyamac

a Centre for Water Resources Research, University of KwaZulu-Natal, Pietermaritzburg,South Africab Association for Water and Rural Development, Hoedspruit, South Africac IWR Water Resources, Nelspruit, South AfricaAccepted author version posted online: 15 Oct 2013.Published online: 25 Mar 2014.

To cite this article: Edward Riddell, Sharon Pollard, Stephen Mallory & Tendai Sawunyama (2014) A methodology forhistorical assessment of compliance with environmental water allocations: lessons from the Crocodile (East) River, SouthAfrica, Hydrological Sciences Journal, 59:3-4, 831-843, DOI: 10.1080/02626667.2013.853123

To link to this article: http://dx.doi.org/10.1080/02626667.2013.853123

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A methodology for historical assessment of compliance withenvironmental water allocations: lessons from the Crocodile (East)River, South Africa

Edward Riddell1, Sharon Pollard2, Stephen Mallory3 and Tendai Sawunyama3

1Centre for Water Resources Research, University of KwaZulu-Natal, Pietermaritzburg, South Africaedriddell@gmail.com2Association for Water and Rural Development, Hoedspruit, South Africa3IWR Water Resources, Nelspruit, South Africa

Received 30 September 2012; accepted 23 July 2013; open for discussion until 1 October 2014

Editor Z.W. Kundzewicz; Guest editor M. Acreman

Citation Riddell, E., Pollard, S., Mallory, S., and Sawunyama, T., 2014. A methodology for historical assessment of compliance withenvironmental water allocations: lessons from the Crocodile (East) River, South Africa.Hydrological Sciences Journal, 59 (3–4), 831–843.

Abstract Environmental flow provisions are a legal obligation under South Africa’s National Water Act (1998)where they are known as the “ecological reserve”, which is now being realized in river operations. This articlepresents a semi-quantitative method, based on flow–duration curve (FDC) analysis, used to assess the complianceof the Crocodile (East) River with the reserve in an historical context. Using both monthly and daily average flowdata, we determine the extent and magnitude of non-compliant flows against environmental water requirements(EWRs) for three periods (1960–1983, 1983–2000, and 2000–2010). The results suggest a high degree of non-compliance, with the reserve increasing with each of these periods (14%, 35%, and 39% of the time),respectively, where effects were most pronounced in the low-flow season. The results also suggest that, whilstthe magnitudes of reserve infringements for the latter period are relatively high, there appears to have been someimprovement since the implementation of the river’s operating rules.

Key words environmental flows; compliance; flow–duration curve; South Africa

Méthodologie d’évaluation historique de la conformité aux allocations d’eau environnementale:les leçons de la rivière Crocodile (Est), Afrique du SudRésumé Les approvisionnements en débit environnemental sont une obligation légale en vertu de la Loi nationalesur l’eau de l’Afrique du Sud (1998), où ils sont connus comme la Réserve écologique qui est maintenant encours de réalisation dans la gestion des rivières. Cet article présente une méthode semi-quantitative, basée surl’analyse de la courbe des débits classés, utilisée pour évaluer dans un contexte historique la conformité des débitsde la rivière Crocodile (Est) avec la Réserve,. En utilisant les données de débits moyens mensuels et journaliers,nous avons déterminé l’étendue et l’ampleur des débits non conformes par rapport aux besoins en eau envir-onnementale pour trois périodes (1960–1983, 1983–2000 et 2000–2010). Les résultats montrent que la Réserven’a souvent pas été respectée, la situation s’aggravant au cours du temps (respectivement 14%, 35%, et 39% dutemps de débits inférieurs à la Réserve pour les trois périodes considérées), les effets les plus prononcés étantobservés au cours des étiages. Les résultats suggèrent également que, même si l’ampleur des atteintes à la Réservepour la dernière période sont relativement élevés, il semble y avoir eu une certaine amélioration depuis la mise enœuvre des règles d’exploitation de la rivière.

Mots clefs débit environmental ; conformité ; courbe des débits classés ; Afrique du Sud

1 INTRODUCTION

There is a large body of supporting evidence whichsuggests that modifications to streamflow regimesinduce ecological alterations in freshwater

ecosystems; thus, there is a need for environmentalflow management in flow-altered rivers (Poff 2009).In turn, there is a need to mimic the components of ariver’s natural flow variability, taking into

Hydrological Sciences Journal – Journal des Sciences Hydrologiques, 59 (3–4) 2014http://dx.doi.org/10.1080/02626667.2013.853123

Special issue: Hydrological Science for Environmental Flows

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consideration the magnitude, frequency, timing,duration, rate of change, and predictability of flowevents (Arthington et al. 2006). Quantifying thisenvironmental flow requirement (EWR), or “ecolo-gical reserve” as it is termed in South Africa, isabout determining the water quantity and qualityrequirements of rivers, estuaries, wetlands, andaquifers to ensure that they are sustained in a pre-determined condition (Hughes 2001). In order toachieve this, some basic approaches are used tomimic natural flow regimes, for instance, from“reference” streams in a region. The alternative isto model a river’s natural flow prior to the periodwhen land-use and management actions in thecatchment modified its flow. In both cases, theobjective is to then extract ecologically meaningfulflow variables from the resulting hydrograph thatcaptures the river’s natural flow variability.

Meanwhile, the evaluation of success is criticalwhen implementing environmental flows to ensuregiven flow conditions are adequate to conserve theriver ecosystem. As a result, the health of the rivermust be monitored (Acreman 2004). Two keyplayers in this monitoring are the decision-makers,who balance the needs of abstractors with those ofthe environment, and the scientists, who researchthe relationships between river flows and the healthof the aquatic ecosystems. Stakeholder participationin decision-making is also becoming morewidespread, and is also a legal requisite in SouthAfrica, where a range of interested parties, fromabstractors to conservationists and local communityrepresentatives, play a key role in influencing deci-sions (Acreman 2005). It is critical, therefore, thatthis shared decision-making is based on sound datarelating to the status of the water resource, throughwhich the environmental flow monitoring will thenform a key operational component of river manage-ment. To this end, trade-offs for various uses interms of river basin water allocation, includingenvironmental flow provision, have to be assessed.This process then allows a basin development levelto be agreed upon, which then becomes the desiredstate for the river condition. The subsequent flowregime, accounting for abstractions to meet the pre-scribed river basin development and water utiliza-tion scenario, then becomes the environmental flow.The implementation of the specified flow regime isthe critical next step. Should this fail, then all thescientific, legislative, and other developments toachieve the desired river state also fail (King andBrown 2006).

In South Africa, environmental flow monitoringand subsequent adaptive management of waterresources are in their early stages, but do serve twokey purposes: first, to ascertain that the agreed-uponflow is being delivered to selected control points alongthe river; second, to ensure that the chosen flow regimeis achieving the desired ecological state. Secondarypurposes include an assessment of whether scientificprediction of ecological state changes is accurate, aswell as providing metrics of sustainability to a catch-ment water manager. The incorporation of monitoringwithin an adaptivemanagement framework is importantfor making decisions in an uncertain knowledge envir-onment where there is a risk of continually making thesame poor management decisions (King and Brown2006).

In the past the environmental flow requirements ofSouth African rivers were determined according to theBuilding Block Method (BBM; King and Louw 1998).As South African natural flow regimes have long beenrecognized as being highly variable, the BBM processdefines a set of blocks that can be considered to applyduring “normal” years (referred to as the “maintenance”requirements), as well as a set that should be appliedduring drought years (“drought” requirements), Hughes(2001). These led to the adoption of the in-stream flowrequirements (IFRs), which represent monthly values ofdaily average flow requirements, or tables of monthly“building blocks”. However, Hughes (1999) empha-sized that these are not sufficient for incorporatinginto the type of water resource systems models thatare used in South Africa. The main drawback of theIFR is that, while the structure and definition of thebuilding blocks imply variations in required flows overtime, they do not provide temporally dynamic informa-tion on the frequency of occurrence, or assurance levels,of the different flows. Problems related to catchmentscale, and variations in the relative magnitudes of lowand high flows, even between closely adjacent catch-ments, are avoided by dealing with flow–durationcurves (FDCs) instead of actual flow values. A FDCis a very informative method for displaying the fullrange of river discharges from low flows to floodevents. It is a relationship between any given dischargevalue and the percentage of time that this discharge isequalled or exceeded (Smakhtin 2001).

This has led to the more recent adoption of EWRFDCs, which account for the ecological “buildingblocks” of flow by providing the variability and fre-quency information required for implementation inoperational river management in South Africa.Hughes and Hannart (2003) detail the Desktop

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Reserve Model, which provides a low-confidenceinitial determination of environmental flow require-ments. This uses regional parameters for SouthAfrican catchments utilizing components of the BBMinto continuous calendar month assurance rules, orfrequency curves. These rules account for, and distin-guish between, both high and low flows, as well asmaintenance and drought year flow requirements. Useof the Desktop Reserve Model is usually a key com-ponent of comprehensive reserve determinations com-bining site-specific ecological assessment with anexpected hydrological regime. Environmental flowsin South Africa are managed according to specifiedriver ecological classes, of which there are four (A–D):where “A” refers to a condition that is largely natural,while “D” assumes a largely modified condition wherethere is a large loss of natural habitat, biota, and basicecosystem functioning (Hughes 2001). The SouthAfrican Department of Water Affairs (DWA) is cur-rently gazetting Management Classes (MC), of whichthere are three, under its Water Resource ClassificationSystem (WRCS), where the environmental flows willbe set according to Resource Quality Objectives(RQOs) in all Water Management Areas (WMA). Atthe time of writing, these MCs had not been set for theInkomati WMA, where the presently prescribed envir-onmental flows are termed “preliminary reserves”,which are purely related to a specific ecological classof river. These preliminary reserves are used in theanalysis presented herein, as they have also been usedin the process to operationalize the reserve in thisWMA. The objectives of this study were two-fold:

(a) Develop a non-intensive desktop methodologyfor retrospective assessment of the performanceof a river in meeting a prescribed EWR, referredto hereafter simply as “compliance”.

(b) Use the approach to explore catchment manage-ment factors, in the broadest possible sense, thathave fostered the extent (% time in a period),magnitude (volumetric infringements), and con-tiguity of “non-compliant” flows.

Whilst the EWRs in South Africa are set for the fullrange from low (baseflow) to high (flood peak) flows,the scope of this article assesses the low-flow compo-nent only. This is because the rivers in northern SouthAfrica are strongly seasonal, where the constraints onmeeting the reserve are suspected to be greatest in thelow-flow/dry winter months (May–September) whendemand on the water resource may be proportionallygreater than in wet summer months. The study usesthe Crocodile (East) River, in northeastern South

Africa as a test case, since this particular system is atthe forefront of implementing Integrated WaterResource Management (IWRM) principles in thecountry. It is anticipated that this analysis may providea valuable IWRM context for management of the riverwhen moving into advanced stages to operationalizeIWRM practices in the system.

2 CASE STUDY AREA

2.1 The Crocodile (East) River

The Crocodile (East) River is the largest primarytributary of the transboundary Incomati River basin,shared between the Republic of Mozambique, theRepublic of South Africa, and the Kingdom ofSwaziland (Fig. 1), and falls within the SouthAfrican Inkomati Water Management Area (DWAF2009). The main stem of the Crocodile (East) Riverruns approximately 320 km, draining an areaapprox. 10 400 km2 before it has confluence withthe Komati River. The Crocodile River lies within asummer rainfall region (October–March) and istopographically diverse, typically divided intothree areas: the western upper plateau (highveld)with moderate rainfall (~730 mm year-1); middlemountainous/escarpment regions (middleveld) withhigh rainfall (~1600 mm year-1); and the easternsub-tropical region (lowveld) with lower rainfall(550–850 mm year-1).

Dominant land use in the catchment is drylandcrops (maize) and grazing in the highveld region,exotic plantation (pine, eucalyptus) in the centralescarpment region, and irrigated agriculture (sugar-cane, vegetables, and citrus) in the lowveld region.By far the largest water use occurs in the lowveld(DWAF 2009). The Kruger National Park (KNP)conservation area also forms part of the easternCrocodile catchment. The water resource infrastruc-ture is considered to be extensively developed dueto large urban centres such as Nelspruit, as well assemi-urban former “homelands” (or Bantustans, thename given to ethnically separate enclaves withinthe borders of the Republic of South Africa, intowhich the majority of the African population wasmoved under the apartheid regime between 1948and 1990).

The large existing demands and further antici-pated expansion in use, via municipal supply andemerging previously disadvantaged farmers, meanthat the catchment is already highly stressed andrunning into deficit (Pollard et al. 2011).

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Furthermore, this increasing pressure to allocatescarce resources is a cause for concern in meetingthe EWRs of the river (McLoughlin et al. 2011).Importantly, this concern is confounded by therecently recalculated natural hydrology for theCrocodile River, which suggests that mean annualrunoff is between 7% and 14% lower than previousestimates (DWAF 2009). Hence, the yield from thecatchment available to emerging uses is likely to runinto deficit much earlier than expected.

2.2 Catchment management historical context

Carmo Vaz and van der Zaag (2003) and Pollard anddu Toit (2011) have provided overviews of the his-tory of water resources management for the Incomatibasin as a whole. In the context of the CrocodileRiver sub-catchment, we suggest three distinct geo-political and socio-economic periods that are used asthe basis for the analysis presented here:

(a) 1960–1983: Represents a period of increasingwater resources development throughout thecatchment both for agriculture and municipalsupply (this is also the era of homelandcreation).

(b) 1983–2000: The construction of Kwena Dam in1980, leading to the reversal of flow seasonalityand fostering an increase in irrigated agriculture,with further municipal expansion.

(c) 2000–2010: Water resource management beginsin earnest with promulgation of the SouthAfrican National Water Act (NWA 1998) andthe signing of international treaties for theshared resources of the Incomati basin (1999Piggs Peak Agreement; 2002 Interim Inco-Maputo Agreement, IIMA).

Catchment management is facilitated by river systemoperations via the Inkomati Catchment ManagementAgency (ICMA), who are mandated to manage theriver according to IWRM principles enshrined in theNWA (1998). The Kwena Dam in the upper catch-ment is the only large dam on this system, but iscrucial for assuring supply to downstream farmers(45% of demand, ICMA 2010) and provision ofenvironmental flow and basic human needs require-ments (23% of demand, ICMA 2010). The Crocodile(East) River is also managed to ensure provision of45% cross-border flows into Mozambique (55% ismet by the Komati River through dual operation ofDriekoppies and Maguga dams by the Komati Basin

Fig. 1 The Incomati Transboundary River Basin (the Crocodile sub-basin is outlined; X2H010, X2H012, X2H014,X2H015, X2H022 are the reference gauges used in this study).

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Water Authority, KOBWA), according to the total2.6 m3 s-1 required to meet the minimum agreedflows at Ressano Garcia that enter Mozambiquefrom South Africa, as stipulated in the IIMA (TPTC2010).

3 METHODS

3.1 Assessment of non-compliance using the EWR

The assessment of compliance/non-compliance withthe ecological reserve in the Crocodile (East) Riverrequired the identification of a driver site for analysis.In this case the most downstream EWR (or ecologicalreserve) site is EWR6 at Nkongoma (25°23′25.8″ S;31°58′28.0″ E), as shown in Fig. 1. This site isadjacent to the KNP and is the last EWR site onthis river before its confluence with the KomatiRiver, within a few kilometres of the border withMozambique. The nearest gauged flows for thisEWR site is the South African DWA gaugeX2H016 at Tenbosch (25°21′50″ S, 31°57′20″ E),the approximate distance along the river coursebetween these two sites is 6.7 km. Gauge X2H016is also an important gauge for monitoring theCrocodile (East) rivers contribution to cross-borderflows of the Incomati River as part of the IIMA.

Care was taken to ensure that the most up-to-dateEWRFDCs for theCrocodile (East) Riverwere selectedfor use in the analysis, for a “C” recommended ecolo-gical class (REC). This was the recommended class atthe time of analysis, since the final class had yet to be set(ICMA 2010). Thus the preliminary C class FDC ruletable used for this analysis is displayed in Table 1 andemanates from a comprehensive reserve determinationstudy (DWAF 2010). The daily and monthly data forthis gauge were accessed via the DWA hydrology pageat http://www.dwa.gov.za/hydrology/. In terms of themonthly data, the DWA gauge data was then “cleaned”to remove poor or inconsistent data as specifiedby DWA.

Since most EWR rule tables are in units ofaverage daily flows in m3 s-1, the daily flow datarequired no conversion. However, total monthly flowdata are given in values of million m3 (hm3) permonth. These were therefore converted to an equiva-lent average daily flow in m3 s-1.

In order to express data graphically along an FDCthese data were then compiled into values for eachmonth, i.e. “all October flows” and “all Novemberflows”, and so on. We present data according to thehydrological year where month number 1 relates to

October and 12 to September, the convention used forthe eastern seaboard of South Africa. These monthly/daily data were then separated into periods of interestfor this study: 1960–1983, 1983–2000, and 2000–2010, before being transformed to the same formatas the EWR rule tables, in the form of FDCs usingthe method of Vogel and Fennessey (1994).

The historical daily flow data were also sub-jected to double-mass analysis for qualitative uncer-tainty analysis using the method of Slarcy andHardison (1966). Since the Crocodile River is ahighly modified catchment, the reference flow pat-tern was determined from five gauges along itstributaries (X2H010, X2H012, X2H014, X2H015,and X2H022), which are shown in Fig. 1.

3.2 Determination of the extent of reservenon-compliance

The resultant FDCs were then incorporated into anXY scatter plot along with the EWR curve for thatmonth, as in Fig. 2. The point at which the averagedaily flow falls below the EWR curve was taken asthe point where flows at this section of river weredeemed non-compliant with the reserve. Thus thispoint is read-off from the x-axis and subtractedfrom 100% to yield the percentage of time withingiven months that the ecological reserve was not met.A similar methodology, for example, has beenapplied in scenario analysis for assessing multi-sec-torial streamflow allocation planning, accounting forreserve requirements in small to medium sized catch-ments in South Africa by Hughes (2006).

The tallied results allow one to assess the extent ofnon-compliance with the ecological reserve in terms of:

– percentage of time this occurred during any givenmonths;

– total number of months non-compliance occurredover a period of interest; and

– seasonality, i.e. did non-compliance occur duringwet months (November–March), or dry months(May–October).

3.3 Magnitudes of non-compliance

To take the study a stage further, in order to under-stand the nuances of non-compliance, additional ana-lysis was required to determine the magnitudes bywhich the ecological reserve was not met. This neces-sitated conversion of both the non-compliant flow andits corresponding reserve value into volumetric

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Tab

le1Site-specificassurancerulesformeetin

gtheecological

reserveClass

Cat

Crocodile

River

EWR6.

Top:

totalreserve(low

andhigh

flow

s);Middle:

low-flow

reserve;

Bottom:naturalflow

s.Dataaregivenin

m3s-1meanmonthly

flow

.

Desktop

Version

2,Printed

on10

Aug

ust20

09Sum

maryof

IFRrule

curves

for:CE6Natural

Flows

Determinationbasedon

definedBBM

Table

with

site-specificassurancerules.

RegionalTy

pe:E.EscarpERC

=C

Mon

th10

%20

%30

%40

%50

%60

%70

%80

%90

%99

%

%Points

Oct

2.66

2.65

2.64

2.63

2.59

2.52

2.41

2.24

2.04

1.88

Nov

10.06

10.03

9.94

9.76

9.41

8.78

7.75

6.26

4.50

3.18

Dec

11.54

11.50

11.40

11.19

10.79

10.08

8.93

7.29

5.35

3.90

Jan

17.71

16.42

15.29

14.26

13.20

11.44

10.21

8.47

6.46

4.97

Feb

34.62

31.66

29.10

26.81

24.56

20.77

18.35

14.87

10.78

7.74

Mar

21.20

19.92

18.78

17.72

16.60

14.69

13.18

10.99

8.40

6.46

Apr

10.19

10.17

10.11

9.99

9.76

9.32

8.60

7.52

6.23

5.26

May

7.82

7.81

7.77

7.69

7.53

7.22

6.70

5.91

4.94

4.20

Jun

6.14

6.14

6.11

6.06

5.94

5.72

5.35

4.77

4.06

3.52

Jul

4.47

4.47

4.45

4.42

4.35

4.21

3.96

3.58

3.10

2.73

Aug

3.07

3.07

3.06

3.04

3.00

2.92

2.78

2.58

2.32

2.12

Sep

2.52

2.51

2.51

2.49

2.46

2.40

2.30

2.15

1.96

1.82

Reserve

with

outhigh

flows

Oct

2.66

2.65

2.64

2.63

2.59

2.52

2.41

2.24

2.04

1.88

Nov

4.05

4.04

4.02

3.98

3.91

3.77

3.54

3.21

2.83

2.54

Dec

5.72

5.71

5.68

5.61

5.48

5.26

4.89

4.36

3.74

3.28

Jan

8.24

8.21

8.15

8.03

7.82

7.45

6.87

6.04

5.08

4.37

Feb

12.56

12.53

12.44

12.27

11.95

11.37

10.44

9.10

7.53

6.35

Mar

11.72

11.69

11.62

11.46

11.17

10.63

9.76

8.49

6.99

5.87

Apr

10.19

10.17

10.11

9.99

9.76

9.32

8.60

7.52

6.23

5.26

May

7.82

7.81

7.77

7.69

7.53

7.22

6.70

5.91

4.94

4.20

Jun

6.14

6.14

6.11

6.06

5.94

5.72

5.35

4.77

4.06

3.52

Jul

4.47

4.47

4.45

4.42

4.35

4.21

3.96

3.58

3.10

2.73

Aug

3.07

3.07

3.06

3.04

3.00

2.92

2.78

2.58

2.32

2.12

Sep

2.52

2.51

2.51

2.49

2.46

2.40

2.30

2.15

1.96

1.82

Natural

DurationCurves

Oct

22.05

17.99

14.15

13.07

11.67

9.95

9.51

8.62

7.79

6.71

Nov

41.60

35.80

29.40

25.20

21.51

18.65

17.37

15.98

12.07

10.26

Dec

83.32

56.72

43.53

38.94

31.11

28.73

25.65

22.45

17.35

12.06

Jan

131.41

78.09

60.04

53.08

44.01

37.32

31.37

27.72

25.24

16.53

Feb

174.12

124.92

77.01

54.74

46.63

41.80

35.62

31.11

26.07

22.26

Mar

135.19

68.68

60.67

51.93

41.14

34.16

30.05

26.49

22.13

17.75

Apr

60.04

46.48

40.39

33.96

30.26

27.43

24.44

23.38

18.00

14.02

May

30.91

26.20

23.17

21.98

20.53

18.99

17.67

16.54

13.37

10.28

Jun

22.99

19.80

17.52

16.99

16.00

15.09

14.01

12.81

10.74

9.49

Jul

19.19

15.80

14.28

13.29

12.91

12.19

11.27

10.41

9.19

7.87

Aug

15.85

13.50

11.63

10.96

10.65

10.28

9.52

8.99

7.88

6.94

Sep

15.12

12.20

11.27

10.02

9.53

9.16

8.58

8.05

7.01

6.22

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equivalents for the month in equation (1). An exampleis shown in Fig. 3, where a flow is observed to bebelow the reserve requirement between the 80th and90th percentiles. In this hypothetical example, a dailyaverage flow value of 1 m3 s-1 was recorded during acertain May month in the period of interest, and it wasdistributed on the 89th percentile. Since the actualflow value is known, but the reserve requirement isnot known for the 89th percentile, this value is inter-polated in a spreadsheet function based on knownreserve requirements at the 80th and 90th percentiles,which is calculated as 1.56 m3 s-1. Thus the reservewas not met in this particular case by 0.56 m3 s-1.

The total monthly equivalent volume for boththe ecological reserve and the non-compliant floware then determined as follows:

Qm ¼ QðTdÞ=106 (1)

where Q is average daily discharge, Td is the totaltime in days for a given month, and Qm is totalmonthly volume (accumulated discharge). Thus, inthe example described in Fig. 3, the total monthlyvolumetric reserve requirement was 4.18 hm3, theaverage monthly flow was 2.68 hm3, and so thereserve was not met by some 1.5 hm3.

3.4 Contiguity of non-compliance

In order to assess whether the river was non-compli-ant with meeting the environmental flow require-ment, a distinction is made between one-off andcontinuous occurrences of non-compliant flows. Forinstance, several successive months of non-compliantflows would be deemed to be a severe infringementon the sustainability of the river.

4 RESULTS AND DISCUSSION

4.1 Flow regime analysis

Figure 4 reveals contextual information on theCrocodile River flow regime overall between 1960and 2010: one can observe a slightly greater averageflow in the first period (1960–1983) than the subse-quent two periods. This is verified with the double-mass plot, where three distinct periods are observed,with slopes of 0.61, 0.17, and 0.14 for 1960–1983,1984–2000, and 2000–2010, respectively. One-wayanalysis of variance revealed that the average dailyflows for these three periods are significantlydifferent (P = 0.00, F = 67.35).

4.2 Extent of non-compliance

The results of the FDC analysis for the three periodsof interest, 1960–1983, 1983–2000, and 2000–2010,

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Fig. 2 FDC for daily average flows at Crocodile (East)River gauge X2H016 for the months of May between2000 and 2010 and the ecological reserve FDC forCrocodile (East) EWR6. Distance c represents compliantflows; nc represents non-compliant flows; and %nc repre-sents the % time that there were non-compliant flowsduring all Mays during the period (in this case ~56%).

NovOct 3.84

4.926.43

1213.8

356.184.87

3.874.38 4.37

4.855.3727.812.77.245.293.773.69 3.62 3.69

3.644.185.315.845.685.244.69

4.23.723.563.54

3.543.534.155.14

5.65.415.044.514.043.56

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4.065.075.085.224.683.843.553.36

3.13.2

2.812.873.554.434.834.844.123.322.922.792.442.77

2.142.342.552.983.354.072.552.342.031.731.992.33

1.181.421.442.012.283.021.791.471.371.221.071.18

0.50.530.740.711.341.330.820.650.59

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Fig. 3 Example determination of the difference between an observed non-compliant flow and an interpolated reserverequirement, for hypothetical May months.

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Fig. 4 (a) Historical hydrograph and annual FDC derived from monthly average flow data for X2H016 between 1960 and1983, 1983 and 2000, and 2000 and 2010. (b) Double-mass plot of average daily flow for X2H016 against reference gauges(see Fig. 1).

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Fig. 5 Performance of the Crocodile River to meet Class C environmental water allocations at gauge X2H016 between1960 and 1983, 1983 and 2000, and 2000 and 2010. (Note that the y-axis scales are different.)

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which in this section we term periods 1, 2, and 3,respectively, are shown in Fig. 5. Here, the black linerepresents the modelled natural flow (from WR2005),the light grey line the C class EWR, and the darkgrey (blue) line the observed flows for that month inthe historical period.

There is a clear change in the natural flowregime with increasing flows from October toFebruary during the summer rainfall months; there-after, discharge decreases from late summer into thedry winter period up to September. Furthermore,annually the EWR ranges between 6.2% (January)and 40.8% (May) of natural flow. Key trends in theflow regime emerge on a month-by-month basisfrom Fig. 5:

(a) Between periods 1 and 2, October shows similarflow regimes; however, greater discharges areabsent in period 2. Meanwhile, period 3 showsa significant reduction in discharge overall to aregime close to that required by the EWR. SinceOctober is typically a low-flow month at the endof dry season, the data suggest that abstractionshave increasingly impacted on the yield of thecatchment by period 3. The extension of largeirrigated agriculture and increases in water use atthe lower end of the Crocodile River is thus aplausible explanation for this trend.

(b) November and December generally show a con-tinual decline in discharge from period 1 to 3.

(c) January shows a decline from period 1 to 2,with similarity in flow regime between periods2 and 3.

(d) February, typically the wettest month in thiscatchment, shows no significant change betweenperiods 1 and 2, but a lowering of the flowregime to period 3.

(e) March shows a similar trend to February, with anot-so-significant decline in flow in period 3.

(f) April and May show very similar changes, witha lowering of discharge from period 1 to 2,similar discharge volumes remain at the higherpercentiles of the flow regime in period 3,whilst lower percentiles show higher flowsthan the previous two periods. Possible reasonsfor this include higher baseflows as a result of aclimatic wet-cycle in the latter part of the2000–2010 decade. Alternatively, this mayalso be due to an improvement in river manage-ment resulting from operational releases fromKwena Dam. Further analysis against natura-lized flows would reveal whether the latter

possibility has resulted in reversed seasonalityof flows which have occurred in other parts ofthe Incomati basin.

(g) June, July, August, and September, the winterlow-flow months, all show a significant drop inthe flow regime from period 1 to 2; importantly,there also appears to be an absence of largerdischarges at the lower percentiles of the flowregime in period 2, with further loss of largerdischarges at the lower percentiles in period 3.This suggests that recent management of the riverin the past three decades may have resulted in thepartial homogenization of the flow regime, mostlikely as a result of capturing the flood peaks byKwena Dam. Also significant in these low-flowmonths is the shift left of the inflection pointbetween the observed flow and EWR curves.

4.3 Overall incidence of non-compliance (EWR)

Figure 6(a) shows summary statistics for these threeperiods as percentage of time the rivers flow regimewas non-compliant with the EWR. These resultssuggest that there is a pattern of increasing non-

(a)

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Fig. 6 Summary performance of the Crocodile River tomeet Class C environmental water allocations at gaugeX2H016 for hydrological years between 1960 and 1983,1983 and 2000, and 2000 and 2010; comparison with: (a)using daily average and monthly average flows for thelatter period; and (b) using the total (low and high flowreserve).

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compliance over the three periods since 1960. Theaverage incidence of failure across all months is 14%,35%, and 39% for each period, respectively. Severalaspects to note from this figure are: the stark contrastin non-compliant flows within period 1, as comparedto periods 2 and 3, where there was at least a dou-bling in per cent time non-compliance throughout theyear in the latter two periods. Meanwhile, summerrainfall months (November–March) had very low/orcomplete absence of non-compliance in the first per-iod, whilst the latter two periods had non-compliantflows ~20% of the time. In all three periods non-compliant flows increased in the dry winter months(May–September), but, whilst this occurred 20% ofthe time in period 1, it was typically 40–70% inperiods 2 and 3. The worst cases of failure are evi-dent for the latest period starting in 2001 betweenJune and September (dry season), where there is non-compliance for at least half the time. Non-compliantflows were generally equal, if not greater, in period 3than period 2 throughout the months.

Figure 6(a) also provides a more detailed analy-sis based on daily flow between 2000 and 2010(since the signing of Piggs Peak Agreement and theIIMA, as well as more concerted IWRM practices).During this period, increased or complete compliancewith the ecological reserve would be expected toappear as a result of IWRM implementation.Despite this, the third period indicates a high degreeof non-compliance. Daily average flow data suggestgreater frequency of non-compliant flows in summermonths by between 10% and 30%, and approxi-mately equal agreement during winter months, ascompared to the monthly data. This would beexpected since the monthly data would average outthe wet season rainfall–runoff variability. Themonthly data would also average out the demandvariability in water abstractions during dry spellswithin the wet season. Overall, the percentage timeof failure varied between 30% and 82%, most nota-bly in the dry season, but surprisingly in the wetseason as well. Failures were recorded in all monthswhen daily data were examined.

For additional context, Fig. 6(b) displays the sameperiods, but against compliance with meeting the totalreserve (both low flows and high/flood flows) ratherthan the low flows in isolation. It is noted that, in thiscase, the average incidence of failure across all monthsis 14%, 42%, and 46% for each period, respectively.Dry winter months show similar levels of non-compli-ance with the low flow and total reserves, and this is tobe expected given the strong seasonality in this river

system. Therefore, the increase in non-compliancearises in the wet summer months, as observed in Fig.6(b). Reasons for this are speculative and warrantfurther investigation, but may be due to two principalfactors: first, total reserve non-compliance remains thesame for period 1, which is prior to the construction ofKwena Dam and other smaller dams on the CrocodileRiver’s tributaries; and second, the greatest increase innon-compliance for the total reserve is observed inNovember at the start of the wet season, when typicallydams are at their lowest levels. Both factors suggest asignificant effect of the dams capturing the flood flowsin the river system.

4.4 Magnitude and contiguousness of non-compliance

Figure 7 reveals the magnitude of infringements bywhich the EWR was not met, in order to give contextto the aforementioned results. In order to interpretthis data set it is important to be cognizant of thefollowing:

– the EWR Required Volume (EWRRV) is the flowvolume that is expected to be met at the relevantpercentile for the actual observed flow at thatgauge in a given month; and

– the Observed Flow Shortfall (OFS) is the volumeby which the EWRRV was not met.

Thus, if there is a big gap between the EWRRV andthe OFS, then the magnitude of not meeting thespecified reserve flow is small (i.e. a minor infringe-ment of compliance); however, if the EWRRV andthe OFS are similar, the magnitude of not meeting thespecified reserve flow is large (i.e. a major infringe-ment of compliance); and if the EWRRVand OFS areequal, then the river has effectively ceased flowingand the magnitude of non-compliance wouldbe 100%.

Rainfall data provide additional context to the dataset andwere derived from theWater Resources of SouthAfrica database, the WR2005 (Middleton and Bailey2009), to create an average for the entire catchment.However, since the WR2005 data set had data onlyuntil December 2004, the remaining period (2005–2009) was supplemented with rainfall data from theAgricultural Research Council of South Africa rain-gauge at Nelspruit, in the centre of the catchment.

In Fig. 7, we see that during the 1960s and1970s non-compliance with the EWR rarelyoccurred, given the large continuous periods wherethe river flows were compliant (e.g. 1971–1978).

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Where the river flows were non-compliant, the mag-nitude of the infringement was relatively small, i.e.the volume shortfall was comparatively small; see,for instance, the large gap in EWRRV and OFS dur-ing the non-compliant flows in 1965–1966. However,towards the late 1970s and early 1980s, when agri-cultural developments began to increase in intensity,the frequency of non-compliance increased substan-tially and was largely contiguous in nature, i.e. therewere successive months of non-compliant flows,such as 1979, 1982, and 1983. In this period, themagnitude of non-compliance was large, in that theEWRRV and OFS were similar, if not equal.However, this period coincided with very low rainfalland would be considered a drought period.

During the early and mid-1980s, infringementscontinued to occur and were contiguous but limitedto the dry-season months (May–September), whilst

the magnitudes were relatively minor, given the largegaps between EWRRV and OFS. However, the early1990s had a long period of contiguous and largemagnitude infringements, where the river cameclose to a cessation of flow, given the close relation-ship between the EWRRV and OFS. Whilst this con-tiguity of non-compliance occurred in almost everymonth in the hydrological year, the magnitudes weremore pronounced in the dry winter months. This alsocoincided with a significant and lengthy droughtperiod linked to El niño. A short dry period in 1998also resulted in large and contiguous infringements.

The latest period 2000–2010 showed severalyears of almost contiguous and large infringementswith meeting the reserve (note that in 2000–2001 thegauges on this river system were damaged due to theFebruary 2000 floods and this data on flow is missingfrom the analysis). These infringements coincide with

EWR Required Volume

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dry-season flows, which may be expected given thesignificant demands placed on the lower reaches ofthe Crocodile River by run-of-river irrigation abstrac-tions for perennial cultivation of sugarcane. However,in contrast to period 2 where the magnitudes of theinfringements were close to the total volumesrequired by the EWR, in the latter period theseinfringements were not so great; for instance, if onecompares 1991–1995 with 2002–2005. However, thelast three years of the analysis (2007–2010) show thatthe frequency of infringements has declined and thatthe magnitude of these infringements has alsodeclined. Coincidentally, this is the same period dur-ing which the Inkomati Catchment ManagementAgency became an operational institution. Importantto note is that, under the ICMA’s mandate, consen-sus-driven adaptive river system operations com-menced in earnest from 2009 onwards making useof real-time river information systems. The continuedanalysis of this sort into the future will demonstratewhether this shift from a passive river managementapproach to one that is both active and adaptive willimprove the sustainability of the river use, should oneobserve increasing compliance with the EWR.

4.5 Potential uncertainties in the analysis

Jain (2012) suggests that raising the awareness on theneed for environmental flows should be coupled withmechanisms to ensure compliance with environmen-tal flow releases and management. The outcomes ofthis study show that this can be achieved through arelatively straightforward desktop analysis, which itis hoped will form the basis for future methods oftesting a rivers sustainability performance should thebenchmark be an EWR or similar.

The obvious contention here may be that the ana-lysis used different lengths of record, i.e. for periods 1,2, and 3 the analysis compared 23, 17, and 10 years ofhydrological data, respectively. An increase in thelength of record will increase the number of hydrologi-cal records and, therefore, reduce the effect of hydro-metric errors in the period of interest (Smakhtin 2001).Therefore, there is a probability of a left and/or rightshift in the FDC curve, which could alter the intersec-tion point of the FDC with the EWR curve, giving theinterpretation an element of uncertainty.

Nevertheless, since the analysis here makes useof accurate river flow gauged data, the interpretationcan be said to be at least semi-quantitative giventhese uncertainty bounds. The double-mass analysisalso revealed three distinct hydrological periods in

this river, which tallied with our own suggested rivermanagement periods. This alleviates the uncertaintyin our assumptions on potential impacts on the sus-tainability of the Crocodile River. Furthermore, itprovides a basis upon which non-compliantflows can be interpreted for causality, as well asbeing a means to cross-check the validity of thefindings.

Importantly, it has recently been emphasizedthat there is a plethora of reserve determinationmethodologies available, and these are continuallyevolving, leading to inconsistent application acrossSouth Africa’s river systems, but also elsewhere(King and Pienaar 2011). The same document raisesthe point of formalizing compliance monitoring,since there is no programme as yet that can beused to effect reserve implementation, augmentadaptive management strategies, and to test theassumptions made on the relationships betweenaquatic biota and hydrological regimes. To this end,this relatively simple desktop methodology could beused as part of a formal compliance monitoringprogramme.

5 CONCLUSION

This analysis has revealed interesting changes to theCrocodile Rivers flow regime, between three distincthistorical periods, with an obvious deterioration inflow in these subsequent periods of catchmentdevelopment since the 1960s. This was noted inall aspects of the analysis: extent (% of time), mag-nitude (volumetric), and contiguity of non-compliantflows. Interestingly, the most recent figures sug-gested that, whilst there had been little change inthe contiguity of flows being non-compliant to theEWR, the magnitudes by which these flows werenot met were not as severe as in earlier periods.This suggests that some improvement in the man-agement of the river can be achieved. However, thisalso demonstrates the importance to continuallymonitor all aspects of being non-compliant withthe EWR. To our knowledge, an assessment of ariver’s performance in meeting its stipulated EWRhas not been conducted to date. It represents asound point of departure for future assessments ofsustainability in the context of IWRM implementa-tion and in developing more robust methods forassessing EWR compliance. This is particularlynecessary since EWRs are now often being inte-grated into river systems operations.

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Acknowledgements The authors gratefully acknowl-edge the contributions of two referees based on ear-lier versions of this article.Funding The research described here emanates fromfunding provided by the South African WaterResearch Commission (WRC).

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