title: Stream sediment sources: A comparison between a native forest catchment and a mixed-use pine and pasture catchment in the Waikato Region of New Zealand

authors: Huirama, Manawa Kokiri

subjects: sediment

abstract: Sediment entering streams and rivers is a global concern for water quality. Suspended sediment can reduce visual clarity, light penetration, and amenity values of water. Transported sediment can also smother benthic fauna and flora and increase the infilling of receiving environments such as lakes and estuaries. In New Zealand catchments, there are three primary sources of erosion i) hillslopes through sheetwash and rill erosion ii) stream bank erosion and iii) mass wasting of hillslopes. There has been little research conducted on the relative contribution of sediment sources to fine sediment within New Zealand. However, some limited research in New Zealand, and research from other countries has identified stream bank erosion as a major source of fine sediment.  

The aim of this thesis was to identify the contribution of various erosion sources to sediment in streams. This study tested the hypothesis that stream bank erosion would be dominant in a pasture catchment, and hillslope erosion would be dominant in a native catchment. This study used paired, adjacent headwater catchments with similar sizes, slopes, soils, and underlying geology but contrasting land uses. The Mangaotama catchment was predominantly pastoral land use, with some areas of pine plantation, while the Whakakai catchment had regenerated and pristine indigenous forest. 

Qualitative field surveys were conducted in the Mangaotama catchment (total length 1.3 km with 0.9 km under pastoral land use and 0.4 km under pine plantation) and Whakakai catchment (0.9 km) to assess stream and riparian conditions including stream bank erosion. Stream banks in the Mangaotama catchment were primarily stable (pasture section (left: 64%, right: 65%); pine section (left: 91%, right: 85%)) and the Whakakai catchment was generally stable (left: 84%, right: 86%). Stock damage dominated stream bank erosion in the pastoral section of the Mangaotama catchment (left: 23%, right: 19%), while stream bank undercutting dominated the pine section of the Mangaotama (left: 9%, right: 13%) and the Whakakai catchment (left: 15% and right: 13%). 

Sediment fingerprinting used radionuclides (¹³⁷Cs, ²¹⁰Pbₑₓ, ²²⁶Ra and ²²⁸Ra), to determine the relative contribution of stream bank erosion and hillslope erosion in suspended sediment samples collected during high flow events. The concentrations of all radionuclides were higher in the hillslopes (P <0.001) ((mean ¹³⁷Cs: 5.8 Bq kg⁻¹, std: 2.4 Bq kg⁻¹); (mean ²¹⁰Pbex: 32.5 Bq kg⁻¹, std: 16.0 Bq kg⁻¹); (mean ²²⁶Ra: 24.9 Bq kg⁻¹, std: 2.1 Bq kg⁻¹); (mean ²²⁸Ra: 35.3 Bq kg⁻¹, std: 4.0 Bq kg⁻¹)) of both the Mangaotama and Whakakai catchments than in the streambanks ((mean ¹³⁷Cs: 0.9 Bq kg⁻¹, std: 0.3 Bq kg⁻¹); (mean ²¹⁰Pbex: 8.4 Bq kg-1, std: 4.6 Bq kg⁻¹); (mean ²²⁶Ra: 28.8 Bq kg⁻¹, std: 1.7 Bq kg⁻¹); (mean ²²⁸Ra: 47.2 Bq kg⁻¹, std: 2.2 Bq kg⁻¹)), clearly distinguishing the sources of sediment. A numerical mixing model determined that stream bank erosion was the dominant source of sediment (90%) within both catchments, with the remaining 10% originating from hillslope erosion. 

Simultaneously recorded continuous turbidity and discharge (Q) data were analysed for the previous year (2017). Six flood events were analysed in the Mangaotama and Whakakai catchments (three large events Q > 1,000 l s⁻¹ and three smaller events (Mangaotama: Q between 127 l s⁻¹ to 606 l s⁻¹, Whakakai: Q between 219 l s⁻¹ and 1398 l s⁻¹). Turbidity was greater in the Mangaotama catchment for four events (ranging from 237 NTU to 3,402 NTU) and greater in the Whakakai catchment for two events (1,293 NTU and 1,435 NTU). Strong clockwise hysteresis dominated (5 out of 6) of the flood events in the Mangaotama catchment, suggesting that stream bank erosion was the dominant source of sediment. Weak anti-clockwise hysteresis dominated the Whakakai catchment (5 out of 6) flood events, indicating sources further away from the sample point. Anti-clockwise hysteresis is primarily associated with hillslope erosion, however, in this study, it was most likely attributed to stream bank erosion sources in the upper reaches of the Whakakai catchment. 

Terrestrial photogrammetry was tested, as it is potentially an effective, simple and cost-effective tool to monitor stream bank erosion over time. Further, a baseline was established which could be re-surveyed though it is recommended that further baseline sites be established to provide improved rigour.

Stream bank erosion was the greatest contributor (90%) to stream sediment loads in both the Mangaotama and Whakakai catchments, with the remaining 10% the stream sediment in both catchments being derived from hillslope erosion. Thus, the hypothesis for this study was rejected. This study demonstrates that stream bank erosion is a natural process and can dominate the supply of sediment to river systems even in relatively unimpacted catchments. Catchment managers need to take this into account when considering catchment rehabilitation projects aimed at reducing the delivery of sediment to streams.

text: Stream sediment sources: A comparison between a native forest catchment and a mixed-use pine and pasture catchment in the Waikato Region of New Zealand Sediment entering streams and rivers is a global concern for water quality. Suspended sediment can reduce visual clarity, light penetration, and amenity values of water. Transported sediment can also smother benthic fauna and flora and increase the infilling of receiving environments such as lakes and estuaries. In New Zealand catchments, there are three primary sources of erosion i) hillslopes through sheetwash and rill erosion ii) stream bank erosion and iii) mass wasting of hillslopes. There has been little research conducted on the relative contribution of sediment sources to fine sediment within New Zealand. However, some limited research in New Zealand, and research from other countries has identified stream bank erosion as a major source of fine sediment.  

The aim of this thesis was to identify the contribution of various erosion sources to sediment in streams. This study tested the hypothesis that stream bank erosion would be dominant in a pasture catchment, and hillslope erosion would be dominant in a native catchment. This study used paired, adjacent headwater catchments with similar sizes, slopes, soils, and underlying geology but contrasting land uses. The Mangaotama catchment was predominantly pastoral land use, with some areas of pine plantation, while the Whakakai catchment had regenerated and pristine indigenous forest. 

Qualitative field surveys were conducted in the Mangaotama catchment (total length 1.3 km with 0.9 km under pastoral land use and 0.4 km under pine plantation) and Whakakai catchment (0.9 km) to assess stream and riparian conditions including stream bank erosion. Stream banks in the Mangaotama catchment were primarily stable (pasture section (left: 64%, right: 65%); pine section (left: 91%, right: 85%)) and the Whakakai catchment was generally stable (left: 84%, right: 86%). Stock damage dominated stream bank erosion in the pastoral section of the Mangaotama catchment (left: 23%, right: 19%), while stream bank undercutting dominated the pine section of the Mangaotama (left: 9%, right: 13%) and the Whakakai catchment (left: 15% and right: 13%). 

Sediment fingerprinting used radionuclides (¹³⁷Cs, ²¹⁰Pbₑₓ, ²²⁶Ra and ²²⁸Ra), to determine the relative contribution of stream bank erosion and hillslope erosion in suspended sediment samples collected during high flow events. The concentrations of all radionuclides were higher in the hillslopes (P <0.001) ((mean ¹³⁷Cs: 5.8 Bq kg⁻¹, std: 2.4 Bq kg⁻¹); (mean ²¹⁰Pbex: 32.5 Bq kg⁻¹, std: 16.0 Bq kg⁻¹); (mean ²²⁶Ra: 24.9 Bq kg⁻¹, std: 2.1 Bq kg⁻¹); (mean ²²⁸Ra: 35.3 Bq kg⁻¹, std: 4.0 Bq kg⁻¹)) of both the Mangaotama and Whakakai catchments than in the streambanks ((mean ¹³⁷Cs: 0.9 Bq kg⁻¹, std: 0.3 Bq kg⁻¹); (mean ²¹⁰Pbex: 8.4 Bq kg-1, std: 4.6 Bq kg⁻¹); (mean ²²⁶Ra: 28.8 Bq kg⁻¹, std: 1.7 Bq kg⁻¹); (mean ²²⁸Ra: 47.2 Bq kg⁻¹, std: 2.2 Bq kg⁻¹)), clearly distinguishing the sources of sediment. A numerical mixing model determined that stream bank erosion was the dominant source of sediment (90%) within both catchments, with the remaining 10% originating from hillslope erosion. 

Simultaneously recorded continuous turbidity and discharge (Q) data were analysed for the previous year (2017). Six flood events were analysed in the Mangaotama and Whakakai catchments (three large events Q > 1,000 l s⁻¹ and three smaller events (Mangaotama: Q between 127 l s⁻¹ to 606 l s⁻¹, Whakakai: Q between 219 l s⁻¹ and 1398 l s⁻¹). Turbidity was greater in the Mangaotama catchment for four events (ranging from 237 NTU to 3,402 NTU) and greater in the Whakakai catchment for two events (1,293 NTU and 1,435 NTU). Strong clockwise hysteresis dominated (5 out of 6) of the flood events in the Mangaotama catchment, suggesting that stream bank erosion was the dominant source of sediment. Weak anti-clockwise hysteresis dominated the Whakakai catchment (5 out of 6) flood events, indicating sources further away from the sample point. Anti-clockwise hysteresis is primarily associated with hillslope erosion, however, in this study, it was most likely attributed to stream bank erosion sources in the upper reaches of the Whakakai catchment. 

Terrestrial photogrammetry was tested, as it is potentially an effective, simple and cost-effective tool to monitor stream bank erosion over time. Further, a baseline was established which could be re-surveyed though it is recommended that further baseline sites be established to provide improved rigour.

Stream bank erosion was the greatest contributor (90%) to stream sediment loads in both the Mangaotama and Whakakai catchments, with the remaining 10% the stream sediment in both catchments being derived from hillslope erosion. Thus, the hypothesis for this study was rejected. This study demonstrates that stream bank erosion is a natural process and can dominate the supply of sediment to river systems even in relatively unimpacted catchments. Catchment managers need to take this into account when considering catchment rehabilitation projects aimed at reducing the delivery of sediment to streams.

year: 2019

title: Systems of service delivery: A resilience perspective

authors: Stanley, Peter

subjects: Cross-agency referrals

abstract: This article discusses the efficacy of different methods of referring children for educational psychological services from the perspective of resilience theorising and research. Four referral systems are considered, and they are intake, patch, screening, and cross-agency referrals. It is argued that the intake system, where referrals are received by a central agency from a number of sources, is problematic from a practice as well as a theoretical perspective. The patch approach is where an educational psychologist works in a defined geographical area, and this system is recommended instead because it promotes an in-depth understanding of the particular circumstances of children, parents, and teachers. It is also suggested that geographical patches, plus the screening of students at several developmental points, is the most useful referral approach because it combines comparative standards and local knowledge. As well, cross-agency referrals, which are referrals from other social service agencies, can function as useful sources of clients for psychological services

text: Systems of service delivery: A resilience perspective This article discusses the efficacy of different methods of referring children for educational psychological services from the perspective of resilience theorising and research. Four referral systems are considered, and they are intake, patch, screening, and cross-agency referrals. It is argued that the intake system, where referrals are received by a central agency from a number of sources, is problematic from a practice as well as a theoretical perspective. The patch approach is where an educational psychologist works in a defined geographical area, and this system is recommended instead because it promotes an in-depth understanding of the particular circumstances of children, parents, and teachers. It is also suggested that geographical patches, plus the screening of students at several developmental points, is the most useful referral approach because it combines comparative standards and local knowledge. As well, cross-agency referrals, which are referrals from other social service agencies, can function as useful sources of clients for psychological services

year: 2012

title: Assessment of effects of proposed treated wastewater discharge to the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua)

authors: Dada, Ayokunle Christopher

abstract: After 2019, irrigation operations at the Land Treatment System (LTS) in the Whakarewarewa Forest are scheduled to cease. A number of options and locations have been considered for the discharge of the treated wastewater when the current discharge consent ceases. Following consultations and technical assessments, the preferred option of Rotorua Lakes Council is to upgrade the existing plant to a full Membrane Bioreactor Plant with the addition of an Ultraviolet Disinfection System (or alternative treatment to achieve an equivalent performance in terms of treated wastewater quality). Under this arrangement, wastewater would be subjected to biological, chemical and physical treatment processes, and the treated wastewater discharged through Te Arikiroa Thermal Channel to Sulphur Bay. Rotorua Lakes Council is thus undertaking an environmental impact assessment study to determine the effects of discharging treated wastewater to the thermal channel and Puarenga Bay (Lake Rotorua), with particular reference to aesthetic, water quality and ecological considerations. These considerations include potential effects related to faecal indicator bacteria, nutrient concentrations, metals, dissolved oxygen, and taonga species (native species of cultural significance).
The assessment focused on:
(i)	The projected treated wastewater characteristics;

(ii)	Existing conditions of the receiving water;

(iii)	The sensitivity of the receiving water and the impact of the proposed discharge on water quality and taonga species (native species of cultural significance) in Te Arikiroa Thermal Channel and Sulphur Bay.

The main techniques used to inform the assessment in this study were:
1) Analysis of historical water quality data, 2011-2014;
2) Collection of additional water quality data at Te Arikiroa Thermal Channel and Sulphur Bay and along a transect to quantify spatial variability (sampling in 2016 and 2017);
3) Mass balance dilution modelling to predict water quality in the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua), at a site outside of the assumed mixing zone;
4) Lake ecosystem modelling conducted by Abell et al. (2015) to assess effects related to eutrophication;
5) Background review of biological information and field investigations for taonga species at Sulphur Bay and Te Arikiroa Thermal Channel (2017).

text: Assessment of effects of proposed treated wastewater discharge to the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua) After 2019, irrigation operations at the Land Treatment System (LTS) in the Whakarewarewa Forest are scheduled to cease. A number of options and locations have been considered for the discharge of the treated wastewater when the current discharge consent ceases. Following consultations and technical assessments, the preferred option of Rotorua Lakes Council is to upgrade the existing plant to a full Membrane Bioreactor Plant with the addition of an Ultraviolet Disinfection System (or alternative treatment to achieve an equivalent performance in terms of treated wastewater quality). Under this arrangement, wastewater would be subjected to biological, chemical and physical treatment processes, and the treated wastewater discharged through Te Arikiroa Thermal Channel to Sulphur Bay. Rotorua Lakes Council is thus undertaking an environmental impact assessment study to determine the effects of discharging treated wastewater to the thermal channel and Puarenga Bay (Lake Rotorua), with particular reference to aesthetic, water quality and ecological considerations. These considerations include potential effects related to faecal indicator bacteria, nutrient concentrations, metals, dissolved oxygen, and taonga species (native species of cultural significance).
The assessment focused on:
(i)	The projected treated wastewater characteristics;

(ii)	Existing conditions of the receiving water;

(iii)	The sensitivity of the receiving water and the impact of the proposed discharge on water quality and taonga species (native species of cultural significance) in Te Arikiroa Thermal Channel and Sulphur Bay.

The main techniques used to inform the assessment in this study were:
1) Analysis of historical water quality data, 2011-2014;
2) Collection of additional water quality data at Te Arikiroa Thermal Channel and Sulphur Bay and along a transect to quantify spatial variability (sampling in 2016 and 2017);
3) Mass balance dilution modelling to predict water quality in the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua), at a site outside of the assumed mixing zone;
4) Lake ecosystem modelling conducted by Abell et al. (2015) to assess effects related to eutrophication;
5) Background review of biological information and field investigations for taonga species at Sulphur Bay and Te Arikiroa Thermal Channel (2017).

year: 2018