Impact and Management of Small Farm Dams in Hawke's Bay, New Zealand

<p>In New Zealand, thousands of small dams have been built in agricultural areas for the purpose of providing water storage for stock and/or irrigation. These dams interrupt flow on perennial or intermittent streams; however, almost nothing is known of the downstream impact of these dams on flow regime, water quality, sediment transfer, and channel morphology. The cumulative impact of these dams at the catchment scale is likely to be significant. The present research was undertaken in the Ruataniwha Plains of Central Hawke's Bay. With further agricultural intensification in the region, it is expected that the construction of small farm dams will continue as farmers try to secure more on-farm water storage. This study attempts to quantify the effects of these storages in two parts: a paired catchment field study to determine the downstream effects of small dams, and a modelling study to investigate the cumulative impact of these storages on streamflow volumes at the regional scale. Results from the paired catchment field study suggest that the regulation of a small stream by three dams (total storage 11.6 ML) has lowered annual runoff volumes, decreased peak flows, increased periods of low flow, and lengthened the response time of the stream to storm events, as compared to the adjacent unregulated stream. Higher precipitation volumes in the winter act to reduce the degree of these impacts, although flow volumes are still lower as compared to the unregulated stream. Throughout the winter, ponds are full and connected to the downstream system, leading to more days of flow on the regulated stream. The regulation of flow has lowered stream erosion potentials, as evidenced by differences in channel bed sediment and morphological characteristics between the two streams. The regulated channel is aggradational, with no evidence of channel scour found over its length. Water quality changes are also observed, with lower water quality measured in the regulated stream and in the ponds, and generally higher water quality measured in the unregulated stream. The impact of farm dams on streamflow in two regional catchments was investigated using two off-the-shelf models (TEDI, Source Catchments). Model predictions suggest that the current volume of farm dam storage has decreased average annual flow volumes in the two catchments by approximately 1%. The predicted streamflow decrease is more significant under scenarios of future agricultural intensification. Regional climate change scenarios do not show a large effect on catchment streamflow volumes. In comparison to known catchment characteristics, the two models have limitations related to some of the model assumptions, and to the inability of the rainfall-runoff model to accurately represent seasonality of flow in the study catchments. On the whole, the models seem to be biased towards underestimating farm dam impact at the regional scale. The study concludes that farm dams have already influenced catchment streamflow and related processes to some degree. At present, the majority of small farm dams in New Zealand do not require resource consent from local council authorities for construction. It is reasonable to expect that farm dams will continue to be built, and it is important that further construction is undertaken with a sound knowledge of the cumulative impact these dams have on catchment processes and existing streamflow volumes. Proper management will mitigate some of these impacts. Management recommendations include the compilation of an inventory of small dams and their characteristics, continued field investigations, and refinement of a catchment model in order to provide a flexible platform for exploring further management options in the region. This study represents a critical first step towards integrated land and water management in the Ruataniwha Plains and will have relevance for the study and management of farm dams in other areas of New Zealand.</p>

Impact and Management of Small Farm Dams in Hawke's Bay, New Zealand

<p>In New Zealand, thousands of small dams have been built in agricultural areas for the purpose of providing water storage for stock and/or irrigation. These dams interrupt flow on perennial or intermittent streams; however, almost nothing is known of the downstream impact of these dams on flow regime, water quality, sediment transfer, and channel morphology. The cumulative impact of these dams at the catchment scale is likely to be significant. The present research was undertaken in the Ruataniwha Plains of Central Hawke's Bay. With further agricultural intensification in the region, it is expected that the construction of small farm dams will continue as farmers try to secure more on-farm water storage. This study attempts to quantify the effects of these storages in two parts: a paired catchment field study to determine the downstream effects of small dams, and a modelling study to investigate the cumulative impact of these storages on streamflow volumes at the regional scale. Results from the paired catchment field study suggest that the regulation of a small stream by three dams (total storage 11.6 ML) has lowered annual runoff volumes, decreased peak flows, increased periods of low flow, and lengthened the response time of the stream to storm events, as compared to the adjacent unregulated stream. Higher precipitation volumes in the winter act to reduce the degree of these impacts, although flow volumes are still lower as compared to the unregulated stream. Throughout the winter, ponds are full and connected to the downstream system, leading to more days of flow on the regulated stream. The regulation of flow has lowered stream erosion potentials, as evidenced by differences in channel bed sediment and morphological characteristics between the two streams. The regulated channel is aggradational, with no evidence of channel scour found over its length. Water quality changes are also observed, with lower water quality measured in the regulated stream and in the ponds, and generally higher water quality measured in the unregulated stream. The impact of farm dams on streamflow in two regional catchments was investigated using two off-the-shelf models (TEDI, Source Catchments). Model predictions suggest that the current volume of farm dam storage has decreased average annual flow volumes in the two catchments by approximately 1%. The predicted streamflow decrease is more significant under scenarios of future agricultural intensification. Regional climate change scenarios do not show a large effect on catchment streamflow volumes. In comparison to known catchment characteristics, the two models have limitations related to some of the model assumptions, and to the inability of the rainfall-runoff model to accurately represent seasonality of flow in the study catchments. On the whole, the models seem to be biased towards underestimating farm dam impact at the regional scale. The study concludes that farm dams have already influenced catchment streamflow and related processes to some degree. At present, the majority of small farm dams in New Zealand do not require resource consent from local council authorities for construction. It is reasonable to expect that farm dams will continue to be built, and it is important that further construction is undertaken with a sound knowledge of the cumulative impact these dams have on catchment processes and existing streamflow volumes. Proper management will mitigate some of these impacts. Management recommendations include the compilation of an inventory of small dams and their characteristics, continued field investigations, and refinement of a catchment model in order to provide a flexible platform for exploring further management options in the region. This study represents a critical first step towards integrated land and water management in the Ruataniwha Plains and will have relevance for the study and management of farm dams in other areas of New Zealand.</p>

Entropy generation in thermally radiated hybrid nanofluid through an electroosmotic pump with ohmic heating: Case of synthetic cilia regulated stream

Synthetic cilia-regulated transports through micro and nanofluidic devices guarantee an efficient delivery of drugs and other biological substances. Entropy analysis of cilia stimulated transport of thermally radiated hybrid nanofluid through an electroosmotic pump is conducted in this study. Joint effects of applied Lorentz force and Ohmic heating on the intended stream are also studied. Metachronal arrangements of cilia field coating channel inner side, are liable to generate current in the fluid. After using the lubrication and the Debye-Huckel estimations, numerical solutions of the envisioned problem are obtained. For pressure rise per metachronal wavelength, the pressure gradient is numerically integrated. The analysis reveals that high electric potential results in reducing the heat transfer effects in the flow system. The enhancement of flow is noticed near the channel surface for higher electroosmotic parameters. The irreversibility in the channel decreases when the Helmholtz-Smoluchowski velocity is applied in the opposite direction of the flow and thus produces the fluid friction irreversibility.

Evaluation of seasonal dynamics of fungal DNA assemblages in a flow-regulated stream in a restored forest using eDNA metabarcoding

Investigation of the seasonal variation in the fungal community is essential for understanding biodiversity and its ecosystem functions. However, the conventional sampling method, with substrate removal and high spatial heterogeneity of community compositions, makes surveying the seasonality of fungal communities challenging. Recently, water environmental DNA (eDNA) analysis, including both aquatic and terrestrial species, has been explored for its usefulness in biodiversity surveys. Examining eDNA may allow for the survey of the community over time with less disturbance to the ecosystem. In this study, we assessed whether seasonality of fungal communities can be detected with monitoring of eDNA in a flow-regulated stream in a restored forest. We conducted monthly water sampling in the stream over two years, and used DNA metabarcoding to estimate the taxonomic and functional groups of fungal eDNA in the water. The river water contained taxonomically and functionally diverse DNA from both aquatic and terrestrial fungi, such as plant decomposers, parasites, and mutualists. The DNA assemblages showed a distinct annual periodicity, meaning that the assemblages were similar to each other regardless of the year, in the same sampling season. These seasonal changes were partially explained by temperature alterations. Furthermore, the strength of the one-year periodicity may vary across functional groups. Our results suggest that forest streams act as a “natural trap” for fungal DNA and that studies of fungal DNA in stream water may provide information on the temporal variation of fungal communities inhabiting not only water but also the surrounding ecosystem.

An Assessment of Self-purification of Regulated and Natural Streams

In these latter days it has become topical to reconsider, the technologies and practice of regulated for drainage purposes streams supervision, to find ways how to combine agricultural productivity and restore lost ecological balance at least partially. The article analyzes the influence of natural and regulated stream stretches on water quality and stream self-purification effectiveness. The analysis of nitrate concentration in water samples taken from natural and regulated stream stretches was conducted for the identification of water quality. Nitrate (NO3) concentrations and their alternation during different seasons were studied. The conducted analysis revealed that stream nitrate self-purification is better in natural stream stretches. An average coefficient of self-purification recorded in the course of the research in natural stretches was 0.57, whereas in a regulated stretch – 0.09. On purpose to improve surface-water quality and self-purifi-cation effectiveness it is suggested to naturalize regulated stream stretches, to allow woody vegetation grow on slopes, to encourage meandering, pools and shoals forming processes in floodplains.

Experimental determination of the flood wave transformation and the sediment resuspension in a small regulated stream in an agricultural catchment

This paper presents the methodology used for artificial flood experiments conducted in a small artificial, trained (regulated) channel on the Nučice experimental agricultural catchment (0.5 km2), central Czech Republic, and the results of the experiments. Two series of experiments were carried out in contrasting initial conditions: (a) in summer, when the stream banks were dry, the baseflow was negligible and the channel was fully overgrown with vegetation; and (b) in spring, when the stream banks were almost water saturated, the baseflow was above the annual average, and there was no vegetation present. Within each campaign, three successive flood waves, each with an approximate volume of 17 m3 and peak flow of ca 40 l s−1, were pumped into the upper part of the catchment drainage channel. The transformation of the flood wave and the sediment transport regime within an approximately 400 m long channel section were monitored by measuring the discharge, the turbidity and the electrical conductivity in three profiles along the stream. On the basis of the results, it was concluded that there is a considerable amount of deposited sediment in the channel that can be re-mobilized even by small floods. Part of the recorded sediment therefore originates from the particles deposited during previous soil erosion events. The flood waves initiated in dissimilar instream conditions progressed differently – we show that the saturation of the channel banks, the stream vegetation and the actual baseflow had a strong influence on the flood transformation and the sediment regime in the channel.