Resource Directed Measures for Protection of Water Resources: River Ecosystems

R22: PROCEDURE FOR SELECTING SITES IN INTERMEDIATE AND COMPREHENSIVE DETERMINATION OF THE ECOLOGICAL RESERVE (WATER QUANTITY COMPONENT)

Senior Editor:Delana Louw, IWR Environmental

Contributing Authors:Nigel Kemper, IWR Environmental

Andrew Birkhead, Streamflow Solutions

Editor:Heather MacKay, Department of Water Affairs and Forestry

Lizette Guest, Guest Environmental Management

Version:1.0

Date:24 September 1999

M:\f_rdm_october\rivers\version 1.0\riv_appR22_version1.0.doc

Appendix R22:

Procedure for Selecting Sites in Intermediate and Comprehensive Determination of the Ecological Reserve (Water Quantity Component)

The process for determining the Ecological Reserve (ER) (Quantity) differs according to the level of determination required such as Intermediate or Comprehensive. Related to this is the level of detail required within the site selection. Within this document, reference will be made to these two different levels where applicable.

NB. The flow component of the Ecological Reserve is referred to in this document as the Instream Flow Requirements (IFR)[1].

R22.1Role of IFR sites in quantification of the flow component of the ecological reserve.

The ER (Quantity) is determined during the a specialist meeting where descriptions of flow in parameters such as depth, velocity and water surface level linked to habitat requirements are stipulated. These parameters need to be converted to flows by means of a stage discharge curve for a specific cross-section (See Appendix R17) determined by a hydraulic modelling procedure. These descriptions of flow requirements take place at a specific cross-section/s in the river called an IFR site. To enable the IFRs to be calculated, these IFRs sites should answer to many criteria, the most important being that the sites should represent critical and varied habitats.

The selection of the IFR sites forms the basis of the preparatory work to be undertaken for the IFR specialist meeting.

The water quantity component of the Reserve is set for each of the IFR sites, and it is therefore vital that

  • the sites are selected to provide as much information as possible about the variety of conditions in a river reach
  • that the specialists that need to use these sites to set IFRs for their discipline can relate to the habitat the sites represent.
  • the persons involved in selecting the sites understand and are experienced with the use of sites in IFR studies. (Louw & Kemper 1997)

Therefore, In order to determine the ER of a river, the IFRs at a number of IFR sites need to be determined.

R22.2Minimum data sets

More than one IFR site is usually selected within the system for a number of reasons:

  • Tributaries entering the system may introduce different channel, bank and/or habitat conditions which may need to be considered separately.
  • The Ecological Management Class (EMC) of particular reach of the river may differ.
  • A river system displays biological diversity along its length, and consequently, a single IFR site is unlikely to adequately reflect this range of diversity.
  • Various hydrological stage points are required within the system to cater for the inflows of tributaries and losses down the length of the system.

The confidence of the quantification of the ER is related to various aspects, including the number of IFR sites representing a river reach, and the adequacy of the sites in setting flow. The number of IFR sites in the system influences the cost and time required for the study, especially when it comes to components such as hydrology and hydraulics. The length of the specialist meeting is also influenced by the number of the IFR sites.

The decision as to how many sites are selected is therefore

  • a function of the length and diversity of the river to be assessed;
  • a trade-off between the need to characterise the river adequately and the constraint of time and resources available.
  • a function of the method (Comprehensive or Intermediate) used to quantify the ER.

The limitations of setting flows at individual sites is offset by the general overview of the river provided by other studies forming part of the ER such as the habitat integrity assessment (See Appendices R4 & R5).

The number of IFR sites required for a CER depends on the size and complexity of the study area. However, the following general principles can be applied:

  • Four IFR sites are usually selected as the number that can be accommodated during a one group four day specialist meeting (CER).
  • Based on the experience of IFR specialists, four IFR sites, selected correctly, will normally cater for a river length of 100 - 200 km (CER).
  • A shorter stretch of river does not necessarily imply fewer IFR sites. The number of sites selected will depend on the variety of habitats and reaches in the stretch of river to be assessed.

The selection of four sites falls within the time constraints associated with the Comprehensive ER (CER) following the Building Block Methodology (i.e. 8 months) pending the season when the study is initiated. The sites must be selected during the low flow season and if a study is initiated during the high flow season, the site selection will be delayed until the low flow season.

The CER will be applied for large and/or important rivers. The Intermediate Ecological Reserve Methodolgy (Quantity) (IERM (Quantity)) will probably be applied more often for smaller rivers and smaller developments. The IERM (Quantity) is essentially a scaled down version of the BBM. The same principles for site selection as for the BBM are followed, however the process linked to the IERM will be scaled down. The impacts on flow of smaller developments (for which an IERM would most likely be applied) would be apparent for a shorter stretch of river than where large developments are being planned (as for a CER). It is therefore assumed that two IFR sites will be selected during an IER for a river reach of between 70 and 100 km in length. This decision will be based on the results of step 1, 2 and 4 of the ER process and is therefore an ad hoc decision that will depend on the specific impact of the development amongst others.

R22.3The selection of IFR sites

The IFR site selection is usually managed by the IFR co-ordinator, although a specialist who is familiar with the process could manage the site selection process. For the purpose of this chapter it is assumed that the IFR co-ordinator undertakes the process.

To manage the IFR site selection, the IFR co-ordinator must

  • have previous experience of the use of the IFR sites in an IFR workshop;
  • have a basic understanding of all the disciplines involved with IFR sites and the specific requirements and expectations of the specialists for IFR sites.
  • be able to weigh up the advantages and disadvantages of the different sites and all relevant factors and make an informed decision on which sites to select during the IFR site visit.

The site selection process during the CER (Quantity) is undertaken by a site selection team consisting of the following specialists:

  • Co-ordinator
  • Fish
  • Aquatic invertebrates
  • Riparian vegetation
  • Fluvial geomorphology
  • Hydraulics

The above representation is required to ensure that sufficient clues for each component are present at the IFR sites to enable quantification of the requirements. This leads to the site requiring ecologically diverse and sensitive habitats. However, the hydraulic accuracy of the site is the most important factor, and hydraulic accuracy is usually linked to simple canal-like structures. The process of selecting sites is therefore a negotiated process whereby ecological variability and confidence has to be measured against hydraulic accuracy. If, a good ecological site is selected but with resulting low confidence hydraulics, the specialists can be very accurate and confident about their requirements, but with inaccurate hydraulics, the resulting recommended flows could be meaningless.

For the purpose of the IERM (Quantity), it is recommended that the BBM site selection principles are utilised wherever possible when selecting the IFR sites, but it is acknowledged that a video is unlikely to be available in most cases, and sites will be selected based mostly on the accessibility of sites, within the time constraints. Due to the lack of time available prior to the specialist meeting only one hydraulic calibration (compared to 3 or more within the CER process), over and above the observations made during the site selection visit, will be possible. However, the value of the second calibration will depend on how different the two calibrations are as within a period of two months (the time scale for determining the IER), very similar flows could be experienced. The site therefore has to be as hydraulically simple as possible to facilitate modelling of the hydraulic relationships from possibly a single site observation, but should still provide as many ecological clues as possible, i.e. provide a variety of habitats at different flows. IERM sites will therefore be less complex (hydraulically and ecologically) than sites that can be selected during the CER process (Louw & Birkhead, 1998).

As the IERM (Quantity) is a 'scaleddown' version of the BBM, the same effort cannot be applied when selecting sites. The site selection team will therefore be undertaken by two specialists only:

  • Hydraulician
  • An aquatic scientist (preferably the specialist that forms the coordinating task in the CER) with a basic understanding of the habitat requirements of the various biotic components and of the river's functioning. This person will require experience of BBM site selection and specialist meetings to understand the criteria most often used in selecting sites by the fish, aquatic invertebrate, riparian vegetation and fluvial geomorphological specialists. It would be an advantage if this person were one of the specialists. However, it must be noted that only specialists that have been exposed often to IFR site selection understand how the other specialistsevaluate sites. Fish and invertebrate habitat might be seen as the more vital habitat as these habitats are mostly used to set the base flows. All previous IFR results have indicated that the base flow component forms the largest part of the total IFR flow volume, and higher flows/floods the smaller component (in perennial rivers); it is therefore more important to have the base flows as accurate as possible.

The selection of IFR sites is guided by a number of considerations, including (Louw & Kemper 1998). (The criteria in boldface are the most important and therefore the overriding criteria):

  • The locality of gauging weirs with good quality hydrological data.
  • The locality of the proposed and existing developments.
  • The locality and characteristics of tributaries.
  • The habitat integrity or Present Ecological State (PES) of the different river reaches.
  • The boundaries of Level II ecotypes within the study area
  • The reaches where social communities depend on a healthy river ecosystem.
  • The suitability of the sites for follow-up monitoring.
  • The habitat diversity for aquatic organisms, marginal and riparian vegetation.
  • The suitability of the sites for accurate hydraulic modelling throughout the range of possible flows, especially low flows.
  • Accessibility of the sites.
  • An area or site that could be critical for ecosystem functioning. These are often represented by riffle units, where low flow conditions or the cessation of flow constitutes a break in the functioning of the river, and consequently, the biota dependant on this habitat and/or perennial flow are adversely affected. Pools are not considered critical habitats in perennial system since they are still able to function or at least maintain life during periods of no flow (Louw & Birkhead, 1998).
  • The locality of geomorphologically representative sites.

When selecting IFR sites, the following sequence of events is followed.

  • Define the significant resource (previously described as the IFR study area, now covered by step 1 of the ER procedures.
  • Select river stretches in which IFR sites should be situated.
  • Preliminary selection of possible IFR sites by means of a video (CER) or maps and local knowledge (IERM), i.e. desk-top only.
  • Ground-truthing of possible sites leading to the final selection.
  • Determine cross-sections at the IFR sites.
  • Document the reasoning behind the selection process.
  • Undertake a cross-sectional survey.

Each of the above events will be discussed separately.

R22.4Sequence of events for the selection of IFR sites

R22.4.1Define the significant resource

This step is covered as part of the ER process and described in the Integrated Manual. The study area should be illustrated on a basic map which is used throughout the ER determination and should depict the following:

  • 5 km habitat integrity sectors if relevant
  • Level II ecoregion breaks
  • Locality of existing and proposed developments
  • Gauging weirs
  • Biomonitoring sites if relevant
  • Locality of IFR sites
  • Virgin vs Present Mean Annual Runoff (MAR) at various points in the system.

R22.4.2Selecting a length of river (IFR stretch) in which an IFR site should be situated

Appendix R2 describes the terminology for different parts of rivers on the basis of geomorphology (zone, segment, reach etc). IFR stretches[2] are parts of rivers which may or may not correspond to the geomorphological breakdown of the river, and will be chosen according to specific criteria. An IFR site will be selected in each IFR stretch.

The selection of river stretches is guided by similar considerations as those that influence the site selection.

The IFR stretches are identified by the IFR co-ordinator on a map with input from the hydrologist, geomorphologist and river ecologists with knowledge of the study area. These stretches will be presented to the IFR planning meeting and motivated by the IFR co-ordinator during the CER process. During the IER, local knowledge will be used only as this information is required upfront, prior to any other information becoming available. During the CER, the IFR stretches need to be selected prior to the habitat integrity helicopter flight, the IFR planning meeting and the site selection.

An example of how the IFR stretches were described for the CER determination for the Mvoti River is as follows:

Stretch 1 : Downstream of Mvotipoort Dam and upstream of the Sikoto Tributary.

Stretch 2 : Downstream of the Sikoto Tributary and upstream of the Situndu Dam site.

Stretch 3 : Downstream of the Hlimbitwa Tributary and upstream of the Welverdiend Dam site.

Stretch 4 : Downstream of the Welverdiend Dam site and upstream of the estuary.

R22.4.3Preliminary selection of IFR sites

Determining where possible sites are located in rugged and undisturbed surroundings can be a difficult, frustrating and time consuming process. Most of the small access roads in rural areas are not marked on maps, and driving to all possible access routes on both sides of the river, could double the site selection costs, or the sites selected might not necessarily be the best available. It is seldom possible to get a comprehensive overview of a river from a ground survey.

The process of selecting IFR sites can therefore be aided by means of a helicopter flight which is usually undertaken for the Habitat Integrity analysis during the CER process (Appendix R5) and capturing the river on video. During this flight, the locations of potential IFR sites are recorded using a GPS (Global Positioning System). Somebody in the helicopter should identify and mark possible access routes with possible sites near the access routes. It is advisable for the navigator to do this function since he/she will be situated in the helicopter to have a good view of the river and immediate catchment.

This helicopter flight should take place before the IFR planning meeting and site selection, approximately within the first one and a half months of the study. Most important however is that the flight is undertaken during LOW FLOWS. During high flows, possible sites are inundated and therefore not visible.

From the helicopter survey, a video is available and a GPS database of latitude and longitudes for every 4 seconds of the flight. Any area identified when watching the video can be accurately pinpointed on a map.

The video is viewed by the IFR site selection team to scrutinise the IFR stretches and sites identified during the flight. The objective of this is to eliminate possible IFR sites and to streamline the next step in the process, i.e. the identification of the sites on the ground.

This preliminary IFR site selection is usually undertaken the day before the site selection visit, sometime within the first month and a half of the study period. For cost-effective reasons, the IFR planning meeting (which requires more persons to attend than the site selection team, but includes the site selection team) is held in the morning, followed by the preliminary site selection by means of the video and followed the next day by the site selection visit.

During the IER process, the availability of a video is unlikely. However, due to the value of such a video, all possible effort must be made to obtain this. If however a video is not available, the access routes on 1:50 000 maps, local knowledge and time constraints will guide the process.