Low Impact Development: The Future in Our Hands


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No notes for slide. Development under the low impact development umbrella is generally 1. Development under the Low Impact Development umbrella Development Increasing public access to open space Enhancing biodiversity Visually unobtrusive Of an appropriate scale Made from natural, local materials Based on renewable resources Autonomous in terms of energy, water and waste Locally Adapted, Diverse and Unique Generating little traffic Linked To Sustainable Livelihoods Co-ordinated by a management plan.

You just clipped your first slide! Clipping is a handy way to collect important slides you want to go back to later. Now customize the name of a clipboard to store your clips. Visibility Others can see my Clipboard. Cancel Save. The hourly and daily precipitation data have mean values of 1. From among the many plausible 21st century climate sequences that might affect California, we selected the GFDL model because it has a relatively high sensitivity to greenhouse gas GHG forcings compared to the larger set of Intergovernmental Panel on Climate Change IPCC global climate models and because it has been used successfully in previous studies of climate change in California [ Cayan et al.

Most importantly for the goals of evaluating the effects of future ENSO variability on recharge, the GFDL model projections of precipitation exhibit considerable interannual variability that is significantly related to ENSO [ Cayan et al. The method assumes a similar frequency and timing of events between historical and future precipitation and only accounts for future changes in the mean, maxima, and minima of precipitation events, which is most relevant for the heavily urbanized study area and for evaluating LID recharge efficiency. An LME model is more appropriate than other linear models because it accounts for temporal pseudoreplication, which is a characteristic of monthly to seasonal variability in meteorological data such as precipitation [ Crawley , ].

The LME model also accounts for fixed and random effects; time is the explanatory variable and the data are analyzed with and without the time variable as a fixed and random effect [ Crawley , ]. To evaluate the effect of time on the overall trend in simulated precipitation, we ran the LME model using three different scenarios: 1 time as a fixed effect; 2 time as a fixed effect and random effect; and 3 time only as a random effect. An ANOVA analysis was subsequently run on the output from the three LME model scenarios to determine which model produces the best fit regarding the statistical significance of time as a predictor of change in simulated precipitation [ Helsel and Hirsch , ; Crawley , ].

All input values were derived from the previously described field instrumentation and from water retention curves built from a sediment textural analysis of the sediment cores Table 1. At the irrigated lawn site, the G2 drain gauge records a water drainage flux every 5 min with a data logger. Based on the textural analyses from the sediment cores, six and five soil layers were used in the infiltration trench and irrigated lawn model domains, respectively Table 1.

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The output pressure head field was then used as initial conditions for the transient simulations. The infiltration trench and irrigated lawn models tended to overestimate recharge during the winter and spring likely because of overestimating the actual irrigation input, assumptions of homogeneity of hydraulic properties within the simulated soil layers, and underestimating actual runoff from the irrigated lawn.

During the summer and fall, the models tended to underestimate recharge likely because of uncertainties in the actual ET, particularly during the foggy summer months in San Francisco. Transient simulations from the calibrated models of the infiltration trench and irrigated lawn were run with future predicted precipitation, based on the linearly transformed Mission Dolores station data set and runoff values for the end of the 21st century year — At the irrigated lawn site, the only inputs are P and I.

After this initial equilibrium period, the total potential value remained relatively constant at most of the depths beneath the infiltration trench Figure 6 a and irrigated lawn Figure 6 b sites. The lack of measurements from the sensor at 69 cm bls 3. The total potential response to the fall precipitation events is less apparent beneath the irrigated lawn Figure 6 b due to the daily irrigation that keeps the matric potential values near saturated conditions and apparently dampens changes in the total potential due to precipitation events.


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The substantial precipitation events in January resulted in a sharp and discrete increase in total potentials at all depths beneath the infiltration trench Figure 6 a and a more damped increase at depths beneath the irrigated lawn Figure 6 b , which likely indicates the propagation of a wetting front and discrete recharge events beneath both sites. The variations in the total potentials at the bottom of the infiltration trench profile sensor at cm bls Figure 6 a are likely the response to recharge events causing fluctuations in the perched water table at approximately cm bls.

The constant downward hydraulic gradient and flux are likely controlled by the water storage capacity of the gravel trench and the irrigation at both sites and are similar to gradients beneath some irrigated agricultural fields, such as in the High Plains aquifer [ McMahon et al.

Unlike the nonirrigated lands in the High Plains [ Gurdak et al. Substantial increases in volumetric water content occur at all depths beneath the infiltration trench in response to the precipitation in fall and particularly winter Figure 8 a , and indicate recharge events in response to the precipitation. The variability in volumetric water content beneath the irrigated lawn during summer is a response to daily irrigation and not precipitation.

The volumetric water content generally increases with depth beneath the infiltration trench, which is a result of the perched water table maintaining near saturated conditions at the base of the profile Figure 9 a. The volumetric water content beneath the irrigated lawn decreases with depth and the daily irrigation maintains relatively high volumetric water content at the top of the profile Figure 9 b. The redistribution of water beneath the infiltration trench, as demonstrated for selected wetting 11 June and 15 September and drying 11 July and 22 September cycles Figure 9 , is much more complex than beneath the irrigated lawn.

The observed range June to March in volumetric water content profiles and corresponding water storage is much greater beneath the infiltration trench than beneath the irrigated lawn. In fact, the minimum water storage beneath the infiltration trench is 0. The downward hydraulic gradients and substantially larger water storage in the vadose zone are evidence for larger recharge rates beneath the infiltration trench than the irrigated lawn.

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When accounting for time as a random and fixed effect, there is no apparent statistical evidence to support an increasing or decreasing trend in total daily precipitation in San Francisco over the 21st century with the GFDL A1F1 scenario. Similar findings are reported by Pierce et al. These forecast seasonal changes have similar sign and magnitude as those findings by Pierce et al.

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Compared to Pierce et al. The San Francisco area is drier in the summer Figure 5 , so the difference in percentage change during that time of year represents small amounts of precipitation that are not as important in terms of recharge beneath LID BMPs. Therefore, our forecast future precipitation from the LME downscaling from the single GFDL model are comparable estimates of future precipitation patterns to those forecasts by Pierce et al.

These results are consistent with recent findings of statistically significant changes in the frequency and magnitude of extreme precipitation events over the historical record across the San Francisco Bay area [ Russo et al. Although the recharge rates are substantially greater beneath the infiltration trench, the estimated recharge volume is generally an order of magnitude smaller beneath the infiltration trench 19—41 m 3 than the irrigated lawn 56— m 3 with a similar drainage area m 2 Table 4.

This inconsistency between recharge rates and volumes beneath the two sites is addressed in section 4. However, total annual precipitation is a poor predictor of recharge efficiency beneath the infiltration trench not shown , possibly because of uncertainties in the estimated water budget inputs and outputs. Although the in situ methods are more applicable than the models for monitoring individual recharge events and providing insight into the mechanics of the recharge process, the models can also be used to estimate recharge and identify important processes during historical and future periods where in situ observations are not available.

The smaller recharge rates from the in situ drain gauge may be attributed to the repacking of native sediments during installation that artificially increase the soil bulk density and decrease porosity and hydraulic conductivity in the drain gauge. A single drain gauge may not capture spatial infiltration patterns beneath all LID BMPs, but the installation of our drain gauge near the inflow drain Figure 3 helps to ensure that a large component of inflow is measured by the drain gauge. Most importantly, the in situ methods provide data that are needed to calibrate the models and verify simulated recharge estimates.

Future models may more accurately capture storm events by using a time discretization of minutes instead of hours. The overflow is a function of the maximum storage capacity of the gravel trench, which is estimated at 2. The estimated gravel porosity of 0. Because the infiltration trench collects water from a larger area, to compare recharge volumes beneath the infiltration trench and irrigated lawn we need to consider an equal catchment area. The estimated recharge volume is generally an order of magnitude greater beneath an area of irrigated lawn 56— m 3 with similar area as the drainage area m 2 of the infiltration trench 19—41 m 3 Table 4.

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This somewhat counterintuitive finding of less recharge volume beneath the infiltration trench than the irrigated lawn is a function of the smaller inflow volumes to the infiltration trench 33—52 m 3 than the irrigated lawn — m 3 Table 4. The storage capacity of the gravel trench enables more efficient infiltration and recharge of storm water that would otherwise runoff, as highlighted by the low recharge efficiencies of the excess irrigation water at the irrigated lawn site.

For example, Devinny et al. The increased recharge and groundwater storage beneath small scale, distributed BMPs may also help to increase groundwater discharge to gaining streams and wetlands and create longer baseflow periods that help support and improve important ecological services and functions. The potential downside of BMPs that enhance recharge, particularly in urban environments, is the potential for flooding of basements, foundations, and subsurface transportation infrastructure. Low Impact Development is a radical form of sustainable housing and livelihood which is in tune with the natural environment, it offers us innovative solutions for the environmental, social and economic challenges of the 21st century.

This book outlines the what, why and how of Low Impact Development. In addition to exploring its potential, the book contains inspiring stori Low Impact Development is a radical form of sustainable housing and livelihood which is in tune with the natural environment, it offers us innovative solutions for the environmental, social and economic challenges of the 21st century. In addition to exploring its potential, the book contains inspiring stories from those who have put Low Impact Development into practice, and plenty of ideas of how you can get involved.

It is printed on recycled paper. Get A Copy. Published November by University of Leicester Dept. More Details Original Title. Other Editions 1. Friend Reviews. To see what your friends thought of this book, please sign up. To ask other readers questions about Low Impact Development , please sign up.

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