Monthly macrophyte surveys of the CEH River Lambourn Observatory at Boxford

This study has resulted in the collection of a unique dataset of seasonal macrophyte growth over a six year period, encompassing extreme levels of flow both high and low. Although not analysed the results of the surveys are presented in this report. The data collected would enable subsequent investigation of the impact of weed cuts on the composition, density, cover and recovery time of these species and the relationship between macrophyte growth, hydraulic roughness, flow regimes and sediment transport/deposition

Use of hydraulic rating to set environmental flows in the Zhangxi River, China

Ningbo city, China, is a rapidly growing residential and industrial centre, with a current population of 4 million. Its development has required a major water supply expansion programme providing 400,000 m3 of water per day from the upper reaches of the Zhangxi River by means of a cascade of reservoirs. Water resources management is achieved through operation of two major reservoirs, Jiaokou (75 million m3) and Zhougongzhai (93 million m3). Water is released from the reservoirs, via turbines (generating hydropower), for local industry, irrigated agriculture and public supply along the lower reaches of the River and to maintain the river ecosystem. Surveys of local residents along the Zhangxi River showed its important role in aspects of life, social activity, culture and leisure. Analysis of ecological monitoring data demonstrated the diverse nature of fish, plants and invertebrates within the river. Some elements of the ecosystem have a high local economic value to local people. This paper reports an assessment of the environmental flow needed to support key species in the river ecosystem. It employs hydraulic ratings to define sections of the river where flow velocity reaches 0.5 ms-1, required to stimulate spawning of the moonlight fish, an economically important and indicator species in the river. In two out of 6 cross-sections studied, flow releases from the reservoirs meet the needs of fish. The reservoirs reduce flood flows, which may lead to a loss of deep pools that are essential for the fish to survive during winter month

Evaluating the productivity potential of chickpea, lentil and faba bean under saline water irrigation systems

The information on salinity threshold levels for food legumes when irrigating with saline water is limited and old. In a multi-year study at two sites in the Euphrates Basin, we aimed at (i) evaluating the potential of saline water irrigation for chickpea, faba bean and lentil production; and (ii) using the SALTMED model to determine threshold crop yields based on irrigation water salinity in equilibrium with ambient soil solution salinity. To evaluate 15 accessions each of lentil and chickpea, and 11 accessions of faba bean, three irrigation treatments were used with salinity levels of 0.87, 2.50 and 3.78 dS m-1 at Hassake and 0.70, 3.0 and 5.0 dS m-1 at Raqqa. Aggregated grain yields showed significant differences (p < 0.05) among crop accessions. Calibration and validation of the SALTMED model revealed a close relationship between actual grain yields from the field sites and those predicted by the model. The 50% yield reduction (π50 value) in chickpea, lentil, and faba bean occurred at salinity levels of 4.2, 4.4 and 5.2 dS m-1, respectively. These results suggest that of the three food legume crops, faba bean can withstand relatively high levels of irrigation water salinity, followed by lentil and chickpea

Evaluating land use and management Natural Flood Management potential

Soil use and management as a form of Natural Flood Management (NFM) has potential to increase infiltration and soil water storage above and below ground. As a result, it can slow the flow of water and reduce flooding caused by surface run-off, rivers and groundwater. Here, we report findings from the LANDWISE project, which examined the potential of land use and management in lowland groundwater-fed catchments in the River Thames Basin, England. We focused on five soil classes within two geology types: shallow permeable soils on carbonate geology (Limestone and Chalk) and deep clay soils on mudstone geology; across agricultural land, grassland and woodland. We compared different farming systems, including conventional, innovative and organic agriculture. We gathered empirical evidence of within and between field variation for different soil use and management strategies, through a broad survey of 164 fields and an in-depth survey of 7 sites. We show that both land use and soil type are significant in affecting bulk density. We also show correlation between organic matter and bulk density, which is important for NFM as organic matter content can be controlled by land use and management practices. We adopted a co-production research approach, to deliver usable impacts for farmers who will ultimately deliver NFM through land use change and management. This work will inform policy and design and delivery of agri-environment schemes; such as the soil survey scheme, a key part of the DEFRA soil action plan. It will help co-deliver NFM alongside other ecosystem services

Instream and riparian implications of weed cutting in a chalk river

Macrophyte growth is extensive in the iconic chalk streams that are concentrated in southern and eastern England. Widespread and frequent weed cutting is undertaken to maintain their key functions (e.g. flood water conveyance and maintenance of viable fisheries). In this study, a multidisciplinary approach was adopted to quantify coincident physico-chemical responses (instream and riparian) that result from weed cutting and to discuss their potential implications. Three weed cuts were monitored at a site on the River Lambourn (The CEH River Lambourn Observatory) and major instream and riparian impacts were observed. Measurements clearly demonstrated how weed cutting enhanced flood flow conveyance, reduced water levels (river and wetland), increased river velocities, and mobilised suspended sediment (with associated chemicals) and reduced the capacity for its retention within the river channel. Potential implications in relation to flood risk, water resources, downstream water quality, instream and riparian ecology, amenity value of the river, and wetland greenhouse gas emissions were considered. Provided the major influence of macrophytes on instream and riparian environments is fully understood then the manipulation of macrophytes represents an effective management tool that demonstrates the great potential of working with nature

Littlestock Brook natural flood management pilot: hydrological and water quality monitoring and analysis report

The Littlestock Brook Natural Flood Management (NFM) trial was a pilot project that ran from 2016 to 2022. Key objectives were to reduce flood risk to Milton-under-Wychwood and enhance the river environment. Through partnership working the Environment Agency collaborated with Wild Oxfordshire, the Evenlode Catchment Partnership, Bruern Estate and the local community to deliver NFM measures. UKCEH has undertaken a detailed monitoring campaign to assess the effectiveness of the measures on reducing flood flows and improving water quality. This report describes the monitoring network, observational methods, equipment adopted, the data processing and analysis undertaken

An Integrated and Novel Approach to Estimating the Conveyance Capacity of the River Blackwater

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Application of the Shiono and Knight Method in asymmetric compound channels with different side slopes of the internal wall

The Shiono and Knight Method (SKM) is widely used to predict the lateral distribution of depth-averaged velocity and boundary shear stress for flows in compound channels. Three calibrating coefficients need to be estimated for applying the SKM, namely eddy viscosity coefficient (λ), friction factor (f) and secondary flow coefficient (k). There are several tested methods which can satisfactorily be used to estimate λ, f. However, the calibration of secondary flow coefficients k to account for secondary flow effects correctly is still problematic. In this paper, the calibration of secondary flow coefficients is established by employing two approaches to estimate correct values of k for simulating asymmetric compound channel with different side slopes of the internal wall. The first approach is based on Abril and Knight (2004) who suggest fixed values for main channel and floodplain regions. In the second approach, the equations developed by Devi and Khatua (2017) that relate the variation of the secondary flow coefficients with the relative depth (β) and width ratio (α) are used. The results indicate that the calibration method developed by Devi and Khatua (2017) is a better choice for calibrating the secondary flow coefficients than using the first approach which assumes a fixed value of k for different flow depths. The results also indicate that the boundary condition based on the shear force continuity can successfully be used for simulating rectangular compound channels, while the continuity of depth-averaged velocity and its gradient is accepted boundary condition in simulations of trapezoidal compound channels. However, the SKM performance for predicting the boundary shear stress over the shear layer region may not be improved by only imposing the suitable calibrated values of secondary flow coefficients. This is because difficulties of modelling the complex interaction that develops between the flows in the main channel and on the floodplain in this region