Urban Stormwater Management: Can Tree Roots and Structural Soils Improve Hydraulic Conductivity into Compacted Soils?

Typically, surface precipitation runoff is a key source of flooding and water pollution in urban communities, and the costly and time-consuming process of installing bio-retention basins is one approach to overcoming these challenges. The implementation of structural soils in bio-retention basins designed to receive and retain stormwater provides these systems with additional functions to bear loads and facilitate tree root growth and exploration. The channels that tree roots produce as they grow can also aid in the flow of water down the soil profile. In this study, the potential for tree roots to penetrate compacted soils and increase rates of hydraulic conductivity were examined alongside the use of structural soil in the context of urban stormwater systems. For the first experiment, Pouteria obovata and Calophyllum soulattri together with a control (without tree) were placed in cylindrical planting sleeves surrounded by compacted clay loam at two compaction levels (bulk densities of 1.45 g cm−3 and 1.66 g cm−3). Roots of both species penetrated the compacted soil, and hydraulic conductivity was increased by an average of 50%. In the second experiment, the same species were grown in structural soil, and a geotextile separated the compacted soil (bulk density of 1.66 g cm−3) from the structural soil (compacted). A greater number of roots as well as larger root diameters from Pouteria obovata penetrated the geotextile, and hydraulic conductivity was enhanced twofold when compared to the controls that had no trees. Growing woody rooting plants and installing structural soils within urban stormwater systems may confer benefits of increased water infiltration and enhanced root development, alongside potential overall improvements to tree health for stormwater control systems in urban environments.

Analisis Kapasitas Kolam Retensi Untuk Pengendalian Banjir di DAS Buah Kota Palembang

According to Public Works Office of Palembang City, Buah Watershed is listed as one of priority areas that requires immediate flood management actions. Flat terrain, high rainfall intensity, tidal fluctuation worsens by massive land use change, are major causes that increase surface water runoff. Therefore, retention basins as one of technical solutions are expected to accommodate runoff discharge and reduce flood. This study aims to analyze the existing hydrological conditions of Buah watershed and to simulate the effectiveness of designed retention basins on peak flow reduction. Hydrological analysis using SCS Unit Hydrograph Model, HEC-HMS combine with spatial analysis using GIS in 26 subcatchment areas resulted on peak discharges range from 1,27 m3/s – 15,71 m3/s. Furthermore, there are ​​12 proposed retention basins within study area ranges from ​​0,580 Ha – 3,967 Ha that are designed to reduce the peak discharge. Simulation result of flood discharge reduction using HEC-HMS indicates that the effectiveness of retention basins in proposed locations varies from 0,03% - 80,05% depending on watershed areas, land availability, and the depth of retention basins.

Social Acceptance for Floating Houses as Alternative Residential in Coastal Area

Semarang as a city located in the coastal area is dealing with the some problems, such as rising sea level, land subsidence, scarcity of land and illegal settlers. In order to deal with rising sea level, a polder system is developed in Kemijen (northern of Semarang). This polder system depends on dredging, a pumping station and retention basins to store water. To make the polder function well and reduce the floods, the existing retention basins should be expanded. Therefore, people who are living at the borders of these basins should be relocated or floating houses could be a solution.. This study aims to determine the acceptance of the Kemijen inhabitants towards floating houses as alternative residential in coastal areas. Data collecting in this study were obtained through interviews with the Kemijen residents and stakeholders. The data then processed by SWOT analysis. Based on the research result, it can be concluded that the social acceptance of the inhabitants is quite low, but there is potential because they see positive elements in a floating house. According to the survey most inhabitants do have insufficient income to pay for a floating house. Building on water is still not legal in Indonesia and therefore the law should probably be adjusted. Besides the land owner is still reluctant in building legal houses on its land. In order to improve the social acceptance of floating houses, these factors should be strengthening, namely relative advantages, compatibility, complexity, trialability and observability.

Alternative approach for works controlling stony debris flows

<p>Many sites of the Dolomites are threatened by channelized debris flows: solid-liquid surges initiated by the entrainment of large quantities of sediments into the abundant runoff at the head of channel incised on fans, can dramatically increase their volume along the downstream routing. This is the case of the Rovina di Cancia site where solid-liquid surges forming in the upper part of the basin can increase their volume up and over 50000 m<sup>3</sup>, seriously impacting the downstream village of Borca di Cadore. The debris-flow channel ends just upstream the village that in the past was hit by four debris flows (three in the recent years) that caused victims and destructions. Control works built until now are not sufficient to protect the village from high magnitude debris flows and a definitive solution calls to be planned. Present works are a flat deposition area, 300 m downstream the initiation area, an open dam under construction downstream it, and  two retention basins at the end of the channel. Between the open dam and the upstream retention basin, there are the rest of eight check-dams made of gabions, built in the 60s and progressively damaged or destroyed by the debris flows occurred after their construction. This series of check-dams limited the entrainment of solid material and the occurrence of localized scours. The initial plan is the substitution of the check-dams with concrete structures and the widening of the dowsntream retention basin through the raising of high elevation embankment downstream it and the following demolition of the actual dyke. Finally, a channel crossing the village and national route on the valley bottom will deliver the fluid phase from the widened basin to the Boite river. All these control works have a very high cost for construction and maintenance and severely impact the village with the presence of a non-negligible residual risk. These drawbacks call for an alternative solution that is searched looking at to the morphology. Downstream of the open dam and on its right side, there is a deep impluvium that ends on a large grass sloping area. The novel solution requires the construction of a channel through the right high bank that deviates the debris flow into the impluvium. The impluvium, widened through the excavation of the surrounding slopes, is closed at the outlet by  an open dam. Downstream the open dam, a channel will lead to a retention basin, where most of storage volume is obtained from the excavation of the grass sloping area, limiting the elevation of the dykes At the end of this basin an open dam will deliver the debris-flow fluid part to a channel passing under the national route and joining the Boite river. Such a solution composed of a deviatory channel, two retention basins (the deep impluvium and that excavated on the sloping grass area) and the channels between and downstream them, has quite a lower costs of construction and maintenance, eliminating the impact on the village because occupying uninhabited areas without interrupting the main roads.</p>