Towards Better Hydrologic Process Understanding at Shell Creek Watershed

Annushka Aliev Author

07/26/2021 Added

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Improving understanding of flooding and rainfall-runoff processes at Shell Creek Watershed, a rural Nebraskan Watershed. This study seeks to determine the relative influence of selected factors on flooding, as well as investigate a potential link between conservation practice implementation and flood reduction observed in the watershed.

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[00:00:01.470]Hello. My name is Annushka Aliev.
[00:00:03.600]I'm an undergraduate researcher from University of Maryland,
[00:00:06.780]and this summer I've been working on improving hydrological process
[00:00:10.170]understanding at shell Creek watershed.
[00:00:14.700]Flooding is a significant and recurring issue in Nebraska,
[00:00:18.270]and one recent example of this is the March, 2019 flood.
[00:00:21.670]This devastating
[00:00:23.130]flood was the culmination of several different factors and forecasting at the
[00:00:27.120]time looked into the interplay of these factors and was able to save lives and
[00:00:31.530]property. In our work,
[00:00:33.930]we are focusing on a specific rural watershed with a history of issues,
[00:00:37.800]including chronic flooding. This history of issues
[00:00:40.980]led to the implementation of lots of conservation practices starting around 2005
[00:00:46.830]in the watershed, which makes it particularly interesting to study.
[00:00:52.200]The main objectives of this study are as follows: to identify
[00:00:56.550]the influence of various factors on flooding and hydrology in Shell Creek; to
[00:01:01.410]develop a rainfall runoff model using artificial neural networks
[00:01:05.280]to predict flooding;
[00:01:07.050]and to conduct a drought intensity
[00:01:09.660]and flood frequency analysis in order to better understand hydrological
[00:01:14.130]processes in the watershed.
[00:01:16.500]And these will have forecasting contribution applications,
[00:01:19.800]as well as lay some groundwork for a future study that is coming down the line.
[00:01:25.710]In order to accomplish these objectives, three main pathways will be used.
[00:01:30.210]The main pathway - this center pathway -
[00:01:32.367]is variable selection and model development,
[00:01:35.340]which will aid in flood prediction and determine the influence of variable
[00:01:39.930]predictive variables on our target variable discharge.
[00:01:44.190]The other two pathways are flood frequency analysis,
[00:01:47.010]which will tell us about changes in probabilities
[00:01:49.980]-flood probabilities- and drought analysis,
[00:01:52.650]which tells us about wet periods and dry periods. Flood frequency analysis
[00:01:57.120]and variable selection in this study, will be run for three periods:
[00:02:01.020]the full period, the non conservation period and the conservation period.
[00:02:06.870]An important thing to note
[00:02:08.159]is that only one gauge provided up-to-date stream flow data,
[00:02:11.610]which was our target variable,
[00:02:13.350]so this gauge limited the time span and scope of our study.
[00:02:17.370]This gauge is indicated with a yellow star on this map.
[00:02:23.400]On the right,
[00:02:24.090]there is a diagram of an artificial neural network, and artificial neural
[00:02:27.870]networks are the machine learning algorithm that we used in our work.
[00:02:34.780]For results,
[00:02:35.500]let's first look at the flood frequency analysis and drought analysis.
[00:02:39.790]On the left, for the flood
[00:02:41.380]frequency analysis,
[00:02:42.640]we compared full period and non conservation period in order to tell us about
[00:02:46.960]the conservation period.
[00:02:48.910]What we learn is that extreme flows are of much greater magnitude in the
[00:02:52.930]conservation period,
[00:02:54.460]but typical flows are actually lower than in previous years.
[00:02:58.810]The drought analysis tells us a bit about soil moisture
[00:03:02.350]- we can find that from the one month SPI - and it also tells us about what dry
[00:03:07.060]periods - this is most clearly agitated by the 12 month SPI. From these,
[00:03:11.920]we learned that soil moisture conditions are typically wetter in spring and
[00:03:15.490]fall and sometimes summer,
[00:03:17.470]and that floods line up fairly well with wet periods in Shell Creek watershed.
[00:03:24.010]From variable selection,
[00:03:25.720]what we find is that no single variable is highly correlated with flooding for
[00:03:30.010]this watershed.
[00:03:31.630]This is also supported by the model performance changes from our leave-
[00:03:35.530]one-out analysis.
[00:03:37.420]The artificial neural network was run without each predictive variable,
[00:03:41.080]and most often this resulted in a prediction performance drop indicating that
[00:03:45.610]the model performs best with all variables included
[00:03:50.680]So what can we learn from these results?
[00:03:53.602]In terms of individual predictability precipitation is most tied to flooding in
[00:03:58.390]Shell Creek watershed. However, this correlation - like the rest - is low,
[00:04:03.430]so we suggest the inclusion of all variables in order to best
[00:04:08.380]predict flooding in Shell Creek
[00:04:10.900]watershed. Of the models we developed in this study,
[00:04:14.500]we suggest the use of the conservation period model as it performed best,
[00:04:19.810]and most closely represents the current conditions in the watershed.
[00:04:26.050]Finally,
[00:04:26.620]we identified that flooding decreased in intensity during the conservation
[00:04:30.670]period, though not necessarily due to conservation practices,
[00:04:34.570]as we noticed that this was a trend that continued from slightly before the
[00:04:38.800]conservation period and can not conclusively attribute decreased
[00:04:43.270]flooding to conservation practices in the watershed.
[00:04:48.820]And that's my work from this summer.
[00:04:50.560]Here are some references that were used in this poster,
[00:04:54.490]and I'd like to thank some people as well.
[00:04:56.710]Funding for this project was provided by the national science foundation and
[00:05:01.000]additional thanks
[00:05:01.810]go out to these people here for connecting us on a more personal level with the
[00:05:06.040]watershed and allowing us to tour it. Thank you.

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Towards Better Hydrologic Process Understanding at Shell Creek Watershed

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